OUTLINE

28.1 Comparison of the and Male Reproductive Systems 843 28 28.1a Perineum 843 28.2 of the Female 844 28.2a 845 28.2b Uterine Tubes 852 28.2c 852 Reproductive 28.2d 855 28.2e External Genitalia 857 28.2f Mammary Glands 857 28.3 Anatomy of the 861 System 28.3a 861 28.3b 863 28.3c Testes 863 28.3d Ducts in the Male Reproductive System 866 28.3e Accessory Glands 867 28.3f 868 28.3g 869 28.4 Aging and the Reproductive Systems 871 28.5 Development of the Reproductive Systems 872 28.5a Genetic Versus Phenotypic 872 28.5b Formation of Indifferent and Genital Ducts 872 28.5c Internal Genitalia Development 874 28.5d External Genitalia Development 874

MODULE 14: REPRODUCTIVE SYSTEM

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he female and male reproductive systems provide the means Table 28.1 Reproductive System Homologues T for the sexual maturation of each individual and produce the special cells necessary to propagate the next generation. In this Female Male Organ Common Function chapter, we first discuss the general similarities between the two Ovaries Testes Produce and reproductive systems and then focus on the specific structures and sex functions of each system. Glans of penis Contain autonomic axons that stimulate feelings of arousal and sexual 28.1 Comparison of the Female climax majora Scrotum Protect and cover some and Male Reproductive Systems reproductive structures Learning Objectives: Vestibular glands Bulbourethral glands Secrete mucin for lubrication 1. Describe the similarities between the female and male reproductive systems. 2. Outline the events of in and males. 3. List the components of the perineum in females and males. Besides their obvious differences, the female and male reproductive organs become fully functional. Also, the gam- reproductive systems share several general characteristics. etes begin to mature, and the gonads start to secrete their sex For example, some mature reproductive system structures are hormones. Puberty is initiated when the hypothalamus sig- derived from common developmental structures (primordia) nificantly increases GnRH (-releasing ) and serve a common function in adults. Such structures are secretion (see chapter 20 ). GnRH acts on specific cells in the called homologues (hō m ́ō -log; homo = same or alike, logos = anterior pituitary and stimulates them to release FSH (follicle- relation) (table 28.1). The structures listed in this table are stimulating hormone) and LH (). (Prior described in detail later in this chapter. to puberty, FSH and LH are virtually nonexistent in boys and Both reproductive systems have primary sex organs girls.) As levels of FSH and LH increase, the gonads produce called gonads (gō nad; ́ gone = seed)—ovaries in females and significant levels of sex hormones and start the processes of testes in males. The gonads produce sex cells called gametes maturation and sexual maturation. (gam ē ́ t; husband or wife), which unite to form a new individ- ual. Female gametes are called , whereas male gam- etes are called . In addition, the gonads produce large amounts of sex hormones ( and in the Study Tip! female and in the male), which affect maturation, A simplified flowchart of the endocrine pathway in puberty is as development, and changes in the activity of the reproductive follows: system organs. GnRH (from hypothalamus) FSH and LH (from anterior pituitary) Both reproductive systems have accessory reproductive Sex hormone release and gamete maturation (in the gonads). organs, including ducts to carry gametes away from the gonads toward the site of fertilization (in females) or simply to the out- side of the body (in males). Fertilization occurs when female and male gametes fuse. The sexual union between a female Both reproductive systems produce gametes. However, the and a male is known as (kop-ū -lā sh ́ ŭn; copulatio = female reproductive tract typically releases a single gamete (sec- a joining), coitus (kō i -t ́ ŭs; to come together), or sexual inter- ondary ) monthly, while the male reproductive tract pro- course. If fertilization occurs, then the support, protection, and duces large numbers (100 million) of gametes (sperm) daily. These nourishment of the developing occurs within the female male gametes are stored within the male reproductive tract for a reproductive tract. short time, and if they are not expelled from the body within that Both the female and male reproductive systems are period, they are resorbed. primarily nonfunctional and “dormant” until a time in ado- lescence known as puberty. At puberty (pū ́ber-tē ; puber = 28.1a Perineum grown up), external sex characteristics become more promi- In both females and males, the perineum (per ́i-nē ́ŭm) is a nent, such as enlargement in females, penis and scro- diamond-shaped area between the thighs that is circumscribed ante- tum enlargement in males, and in both . The riorly by the , laterally by the ischial tuberosities,

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Pubic symphysis Pubic symphysis Urogenital triangle Ischiocavernosus muscle Bulbospongiosus muscle Superficial transverse perineal muscle Ischial tuberosity Anus Anus Anal triangle

External anal sphincter

Coccyx Female Male Figure 28.1 Perineum. In both females and males, the perineum is the diamond-shaped area between the thighs extending from the pubis anteriorly to the coccyx posteriorly, and bordered laterally by the ischial tuberosities. An imaginary horizontal line extending from the ischial tuberosities subdivides the perineum into a urogenital triangle anteriorly and an anal triangle posteriorly.

and posteriorly by the coccyx (figure 28.1). Two distinct tri- angle bases are formed by an imaginary horizontal line extending 28.2 Anatomy of the Female between the ischial tuberosities of the ossa coxae. Both triangles house specific structures in the floor of the trunk: Reproductive System ■ The anterior triangle, called the urogenital triangle, Learning Objectives: contains the clitoris and the urethral and vaginal 1. Describe the gross and microscopic anatomy of the ovaries. orifices in females and the base of the penis and the 2. Explain follicle development, the ovarian cycle, and the scrotum in males. Within the urogenital triangle are process of . the muscles that surround the external genitalia, called 3. Detail the anatomy of the uterine tubes and their function. the ischiocavernosus, bulbospongiosus, and superficial 4. Identify the regions of the uterus, and outline the uterine cycle. transverse perineal muscles. 5. Describe the anatomy of the vagina and the external ■ The posterior triangle, called the anal triangle, is the genitalia. location of the anus in both sexes. Surrounding the anus is 6. Detail the gross and microscopic anatomy of the mammary the external anal sphincter. glands. Review table 11.12 and figure 11.15 as well when learning A sagittal section through the female illustrates the these structures. internal reproductive structures and their relationships to the and (figure 28.2). As the folds around the various pelvic organs, it produces two major dead-end recesses, or WHATW DID YOU LEARN? pouches. The anterior vesicouterine (ves ́i-kō -ū ter-in; ́ vesica = bladder, = ●1 What is puberty? utero uterus) pouch forms the space between the uterus and the urinary bladder, and the posterior rectouterine (rek-tō -ū ter-in) ́ pouch ●2 Compare the structures in the female and male urogenital forms the space between the uterus and the rectum. triangles.

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Ureter Uterine tube

Ovary Fimbriae of uterine tube

Uterus

Rectouterine pouch

Vesicouterine pouch

Urinary bladder of uterus

Pubic symphysis Rectum

Urethra Vagina

Clitoris

External urethral orifice Vaginal orifice Anus Labium minus Labium majus

Figure 28.2 Sagittal Section of the Female Pelvic Region. A sagittal section of the female pelvis illustrates the position of the uterus with respect to the rectum and urinary bladder.

The primary sex organs of the female are the ovaries. The slightly larger than an almond—about 2 to 3 cm (centimeters) long, accessory sex organs include the uterine tubes, uterus, vagina, 2 cm wide, and 1 to 1.5 cm thick. Their size usually varies during clitoris, and mammary glands. each as well as during . The ovaries are anchored within the by specific 28.2a Ovaries cords and sheets of connective tissue. A double fold of perito- The ovaries are paired, oval organs located within the pelvic cav- neum, called the (mez ́ō -vā r ́ ē -ŭm; mesos = middle, ity lateral to the uterus (figure 28.3). In an adult, the ovaries are ovarium = ), attaches to each ovary at its hilum, which is the

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Ovarian Ovarian Suspensory (part of broad ) ligament

Ovarian ligament Infundibulum Uterine tube Fimbriae

Ovary Uterus

Broad ligament

Uterine artery Uterine vein

Ureter (a) Posterior view Cervix Vagina

Uterine tube External os

Tunica albuginea Cortex Medulla Mesosalpinx

Fimbriae

Ovaries

Uterine Mesovarium tube Hilum Uterus Broad (b) Lateral sectional view ligament Round ligament Urinary bladder

Figure 28.3 Internal Organs of the Female Reproductive System. ( a) A posterior view shows the internal organs of the female reproductive system, which include the ovaries, uterine tubes, uterus, and vagina. (b) A lateral sectional view of the ovary shows the mesovarium in relation to the mesosalpinx of the broad ligament. (c) A cadaver photo provides a superior view of the female pelvis and reproductive organs.

(c) Superior view

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anterior surface of the ovary where its blood vessels and 2. A primary follicle forms from a maturing primordial follicle. enter. The mesovarium secures each ovary to a broad ligament, Each primary follicle consists of a primary oocyte surrounded which is a drape of peritoneum that hangs over the uterus. Each by one or more layers of cuboidal follicular cells, which are ovary is anchored to the lateral aspect of the uterus by an ovar- now called granulosa cells. Each primary follicle secretes ian ligament; a suspensory ligament attaches to the lateral edge estrogen as it continues to mature. The estrogen stimulates of each ovary and projects superolaterally to the pelvic wall. The changes in the uterine lining. ovarian blood vessels and nerves are housed within each suspen- 3. A secondary follicle forms from a primary follicle. Each sory ligament, and they join the ovary at its hilum. Smooth muscle secondary follicle contains a primary oocyte, many layers of fibers within both the mesovarium and the suspensory ligament granulosa cells, and a fluid-filled space called an antrum. contract at the time of ovulation to bring the ovaries into close Within the antrum is a serous fluid that increases in volume proximity with the uterine tube openings. as ovulation nears. Surrounding the primary oocyte are two Each ovary is supplied by an ovarian artery and an ovar- protective structures, the and the corona ian vein. The ovarian are direct branches off the aorta, radiata. The zona (zō ń ă; zone) pellucida (pe-lū ś ı̆ d-ā; immediately inferior to the renal vessels. The ovarian exit pellucidus = allowing the passage of light) is a translucent the ovary and drain into either the inferior vena cava or one of the structure that contains glycoproteins. External to the zona renal veins. Traveling with the ovarian artery and vein are auto- pellucida is the corona (kō -rō ń ă; crown) radiata (rā-d ē- ă t́ ă; nomic nerves. Sympathetic axons come from the T10 segments of radiating), which is the innermost layer of granulosa cells. the , whereas parasympathetic axons come from CN X 4. A vesicular follicle (also called a mature follicle or Graafian (vagus ). follicle) forms from a secondary follicle. A vesicular follicle When an ovary is sectioned and viewed microscopically, many contains a secondary oocyte (surrounded by a zona features are visible (figure 28.4). Surrounding the ovary is a thin, pellucida and the corona radiata), numerous layers of simple cuboidal epithelial layer called the germinal epithelium, so granulosa cells, and a large, fluid-filled, crescent-shaped named because early anatomists erroneously thought it was the ori- antrum. A secondary oocyte has completed I and is gin of the female germ (sex) cells. Deep to the germinal epithelium arrested in the second meiotic metaphase. Vesicular follicles is a connective tissue capsule called the (al-bū - become large and can be distinguished by their overall size jin ́ē -ă; albugo = white spot), which is homologous to the tunica as well as by the size of the antrum. albuginea of the testis. Deep to the tunica albuginea, the ovary can 5. When a vesicular follicle ruptures and expels its oocyte be partitioned into an outer cortex and an inner medulla. The cor- (in a process called ovulation), the remnants of the tex contains ovarian follicles (described next), while the medulla is follicle remaining in the ovary turn into a yellowish composed of areolar connective tissue and contains branches of the structure called the (loo-tē ́ŭ m; luteus = ovarian blood vessels, lymph vessels, and nerves. saffron-yellow). The corpus luteum does not contain an oocyte. However, the corpus luteum secretes the sex Ovarian Follicles hormones progesterone (prō -jes ter-́ ō n; pro = before; Within the cortex are thousands of ovarian follicles. Ovarian gestation) and estrogen (es tŕ ō -jen; oistrus = estrus, gen = follicles consist of an oocyte surrounded by follicle cells which producing). These hormones stimulate the continuing support the oocyte. There are several different types of ovarian buildup of the uterine lining and prepare the uterus for follicles, each representing a different stage of development possible implantation of a fertilized ovum. (figure 28.4): 6. When a corpus luteum regresses (breaks down), it turns into a white, connective tissue scar called the corpus 1. A primordial follicle is the most primitive type of ovarian albicans (al bi-kanz;́ white). Most follicle. Each primordial follicle consists of a primary oocyte structures are completely resorbed, and only a few may surrounded by a single layer of squamous follicle cells. A remain within an ovary. primary oocyte is an oocyte that is arrested in the first meiotic prophase. About 1.5 million of these types of follicles are Table 28.2 summarizes the different structures that develop present in the ovaries at birth. during a female’s monthly cycle.

Table 28.2 Ovarian Follicles and Structures That Develop in the Ovary Ovarian Structure Type of Oocyte Anatomic Characteristics Time of First Appearance Primordial follicle Primary oocyte Single layer of fl attened follicular cells surround an Fetal period oocyte Primary follicle Primary oocyte Single or multiple layers of cuboidal granulosa cells Puberty surround an oocyte Secondary follicle Primary oocyte Multiple layers of granulosa cells surround the Puberty oocyte and a small, fl uid-fi lled antrum Vesicular follicle Secondary oocyte Many layers of granulosa cells surround the oocyte Puberty and a very large antrum Corpus luteum No oocyte Yellowish, collapsed folds of granulosa cells Puberty Corpus albicans No oocyte Whitish connective tissue scar, remnant of a Puberty degenerated corpus luteum

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Zona pellucida Primordial Primary Follicle Primary Granulosa Primary Corona Granulosa follicles oocyte cells oocyte cells oocyte radiata Antrum cells

Primary Secondary follicle follicle

LM 500x LM 500x LM 50x

(b) Primordial follicles (c) Primary follicle (d) Secondary follicle

Granulosa cells Zona pellucida Primary oocyte Secondary follicle Antrum Primary follicles Suspensory ligament of ovary

Medulla

Primordial follicles

Tunica albuginea

Germinal epithelium Vesicular follicle Antrum

Secondary oocyte Zona pellucida

Ovarian ligament Corona radiata Zona pellucida Ovulated secondary oocyte Corpus albicans Corpus Developing Cortex (a) Cross section of ovary luteum corpus luteum

Corona Zona Secondary Corpus albicans Corpus luteum Antrum radiata pellucida oocyte

LM 80x LM 25x LM 100x

(g) Corpus albicans (f) Corpus luteum (e) Vesicular follicle

Figure 28.4 Stages of Follicle Development Within an Ovary. The ovary produces and releases both female gametes (secondary oocytes) and sex hormones. (a) A coronal view of the ovary contents depicts the different stages of follicle maturation, ovulation, and corpus luteum development and degeneration. Note that all of the follicles and structures shown in this image would appear at different times during the ovarian cycle—they do not occur simultaneously. Further, the follicles do not migrate through the ovary; rather, all follicles are shown together merely for comparative purposes. Histologic sections identify (b) primordial follicles, (c) a primary follicle, (d) a secondary follicle, and (e) part of a vesicular follicle. After ovulation, the remnant of the vesicular follicle forms (f) the corpus luteum, which then degenerates into (g) the corpus albicans.

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Oogenesis and the Ovarian Cycle Study Tip! is the maturation of a primary oocyte to a secondary To distinguish a primary oocyte from a secondary oocyte, remem- oocyte and is illustrated in figure 28.5. ber that: Before Birth The process of oogenesis begins in a female ■ A primary oocyte is arrested in prophase I (the term “primary” also means “one”). before birth. At this time, the ovary contains primordial germ cells called oogonia (ō -ō -gō n ́ ē -ă; sing., ; oon = ), which are ■ A secondary oocyte is arrested in metaphase II (the term diploid cells, meaning they have 23 pairs of . During “secondary” means “two”). the fetal period, the oogonia start the process of meiosis, but they Additionally, remember that the only containing a are stopped at prophase I. At this point, the cells are called pri- secondary oocyte is a vesicular follicle—all other ovarian follicles have mary oocytes. At birth, the ovaries of a female are estimated primary oocytes only. to contain approximately 1.5 million primordial follicles within its cortex. The primary oocytes in the primordial follicles remain arrested in prophase I until after puberty.

Oogenesis Follicle Development Embryonic and fetal period: (Development of Oocytes)

Oogonia are diploid cells (containing 23 pairs of chromosomes; or 46 total) that are the origin 46 Oogonium of oocytes. Mitotic divisions of oogonia produce primary oocytes, which are diploid cells.

Primary oocytes start the process of meiosis but Primary oocyte Primordial are arrested in the first meiotic prophase. 46 (arrested in prophase I) follicle

Childhood: Ovary is inactive. It houses primordial follicles.

Monthly, from puberty to : Primary follicle Primary oocyte Approximately 20 primordial follicles mature into 46 primary follicles every month. A few of these (remains arrested primary follicles mature into secondary follicles. in prophase I) Secondary follicle

Secondary oocyte (arrests in metaphase II) Vesicular follicle Only one or two of the secondary follicles mature into a vesicular follicle, where the primary oocyte 23 First completes the first meiotic division to produce a polar body and a secondary oocyte. The secondary oocyte (degenerates) Ovulation is a haploid (containing 23 chromosomes only) that is arrested in the second meiotic metaphase. Sperm Ovulated secondary oocyte Meiosis II completed (only if fertilization occurs) If the secondary oocyte is fertilized, it completes the second meiotic division and becomes an ovum. If the 23 secondary oocyte is not fertilized, it degenerates. Second 23 Ovum polar body (degenerates)

Figure 28.5 Oogenesis. Oogenesis begins in a female fetus, when primary oocytes develop in primordial follicles. The ovary and these follicles remain inactive during childhood. At puberty, a select number of primordial follicles each month undergoes maturation and produces a female gamete (secondary oocyte).

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Childhood During childhood, a female’s ovaries are inactive, approaches, the granulosa cells in the vesicular follicle increase and no follicles develop. In fact, the main event that occurs during their rate of fluid secretion, forming a larger antrum and causing childhood is atresia (ă-trē z ́ ē -ă; a = not, tresis = a hole), in which further swelling within the follicle. The edge of the follicle that some primordial follicles degenerate. By the time a female child continues to expand at the ovarian surface becomes quite thin and reaches puberty, only about 400,000 primordial follicles remain in eventually ruptures, expelling the secondary oocyte. the ovaries. The occurs during days 15–28 of the ovarian cycle, when the remaining granulosa cells in the ruptured vesicu- From Puberty to Menopause When a female child reaches puberty, lar follicle turn into a corpus luteum. The corpus luteum secretes the hypothalamus increases its release of GnRH (gonadotropin- progesterone and estrogen that stabilize and build up the uterine releasing hormone), which stimulates the anterior pituitary to release lining, and prepare for possible implantation of a fertilized ovum. FSH (follicle-stimulating hormone) and LH (luteinizing hormone). The corpus luteum has a life span of about 10–13 days if the The levels of FSH and LH vary in a cyclical pattern and produce a secondary oocyte is not fertilized. After this time, the corpus luteum monthly sequence of events in follicle development called the ovar- regresses and becomes a corpus albicans. As the corpus luteum ian cycle. The three phases of the ovarian cycle are the follicular degenerates, its levels of secreted progesterone and estrogen drop, phase, ovulation, and the luteal phase (figure 28.6). causing the uterine lining to be shed as (men-stroo- The occurs during days 1–13 of an approxi- ā sh ́ ŭn), also called menses or a period. This event marks the end of mate 28-day ovarian cycle. At the beginning of the follicular phase, the luteal phase. A female’s first menstrual cycle, called FSH and LH stimulate about 20 primordial follicles to mature into (me-nar ́kē; men = month, arche = beginning), is the culmination of primary follicles. It is unclear why some of the primordial follicles female puberty and typically occurs around age 11–12. in the ovary are stimulated to mature into primary follicles, while If the secondary oocyte is fertilized and if it successfully the remainder remains unaffected by the FSH and LH secretion. implants in the uterine lining, this fertilized structure (now a pre- As the follicles develop, their granulosa cells release the hormone ) begins its own development (as discussed in chapter 3). inhibin, which helps inhibit FSH production, thus preventing The pre-embryo starts secreting human chorionic gonadotropin excessive ovarian follicle development and allowing the current (hCG), a hormone that enters the mother’s bloodstream and acts on primary follicles to mature. the corpus luteum. Essentially, hCG lets the corpus luteum know Shortly thereafter, a few of these primary follicles mature that implantation has occurred and that the corpus luteum should and become secondary follicles. The primary follicles that do not continue producing progesterone, which will build and stabilize the mature undergo atresia. Late in the follicular phase, one second- uterine lining. After 3 months, the of the developing fetus ary follicle in an ovary matures into a vesicular follicle. Under the starts producing its own progesterone and estrogen, so by the end of influence of LH, the volume of fluid increases within the antrum, the third month, the corpus luteum has usually regressed and formed and the oocyte is forced toward one side of the follicle, where it a corpus albicans. is surrounded by a cluster of granulosa cells termed the cumulus (kū m ́ ū -lŭs; heap) oophorus (ō -of ́ō r-ŭs; phorus = bearing). The After Menopause The time when a woman is nearing meno- innermost layer of these cells is the corona radiata. pause is called perimenopause. During perimenopause, estrogen As the secondary follicle matures into a vesicular follicle, its levels begin to drop, and a woman may experience irregular primary oocyte finishes meiosis I, and two cells form (see figure periods, skip some periods, or have very light periods. When a 28.5). One of these cells receives a minimal amount of woman has stopped having monthly menstrual cycles for 1 year and forms a polar body, which is a nonfunctional cell that later and is not pregnant, she is said to be in menopause (men ́ō -pawz; deteriorates. The other cell receives the bulk of the cytoplasm and pauses = cessation). The age at onset of menopause varies con- becomes the secondary oocyte, which continues to develop and siderably, but typically is between 45 and 55 years. Menopause is reaches metaphase II of meiosis before it is arrested again. This reached when there are no longer any ovarian follicles or the fol- secondary oocyte does not complete meiosis unless it is fertilized licles that remain stop maturing. As a result, significant amounts by a sperm. If the oocyte is never fertilized, it breaks down and of estrogen and progesterone are no longer secreted. Thus, a degenerates about 24 hours later. woman’s endometrial lining does not grow, and she no longer has Ovulation (ov ́ū -lā sh ́ ŭn) occurs on day 14 of a 28-day ovar- a menstrual period. ian cycle and is defined as the release of the secondary oocyte from a vesicular follicle (figure 28.6). Typically, only one ovary ovulates each month—that is, the left ovary ovulates one month, WHAT DO YOU THINK? and the right ovary ovulates the next. Ovulation is induced only ●1 If a woman has one ovary surgically removed, can she still become when there is a peak in LH secretion. As the time of ovulation pregnant? Why or why not?

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Ovarian cycle

Primary Secondary Vesicular Ovulation Corpus luteum Regression Corpus follicle follicle follicle forms albicans

Days 1357911 13 15 17 19 21 23 25 27 1

Follicular phase Ovulation Luteal phase

Gonadotropin levels

FSH LH

Days 1357911 13 15 17 19 21 23 25 27 1

Ovulation

Ovarian hormone levels

Estrogen

Progesterone

Days 1357911 13 15 17 19 21 23 25 27 1

Uterine cycle

Menstrual flow Functional layer

Basal layer Days 1357911 13 15 17 19 21 23 25 27 1

Menstrual phase Proliferative phase Secretory phase Figure 28.6 Hormonal Changes in the Female Reproductive System. Cyclic changes in affect ovarian hormone production. FSH causes development of estrogen-producing ovarian follicles during the follicular phase of the ovarian cycle. Estrogen stimulates the proliferative phase in the uterine cycle. Estrogen levels spike as ovulation approaches. High levels of LH promote ovulation at the midpoint of the ovarian cycle. The corpus luteum becomes functional after ovulation, and it produces both progesterone and estrogen to promote uterine lining development. If fertilization does not occur, the corpus luteum degenerates, and menstrual flow begins at the start of the next uterine cycle.

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28.2b Uterine Tubes The uterine tubes, also called the fallopian (fa-lō p ́ ē -an) tubes or CLINICAL VIEW (ō vi-d ́ ŭkt; duco = to lead), extend laterally from both sides of the uterus toward the ovaries (figure 28.7). Fertilization of the Tubal Pregnancy secondary oocyte occurs in the lateral part of these tubes, and the pre-embryo begins to develop as it travels toward the uterus. In a tubal pregnancy (or ectopic pregnancy), the fertilized oocyte Usually it takes the pre-embryo about 3 to 4 days to reach the implants in the uterine tube, rather than traveling to the uterus lumen of the uterus. for implantation. The main danger in a tubal pregnancy is that The uterine tubes are small in diameter, and reach their the uterine tube is unable to expand as the embryo grows. Thus, maximum length of between 10 and 12 centimeters after puberty. the embryo can remain viable no later than week 8, at which time These tubes are covered and suspended by the mesosalpinx it has become too large for the confines of the uterine tube. The (mez ́ō -sal pinks; ́ salpinx = trumpet), a specific superior part of the woman experiences severe cramping, and the uterine tube may broad ligament of the uterus (see figure 28.3a). Each uterine tube is rupture if the embryo is not surgically removed. If the uterine composed of contiguous segments that are distinguishable in both tube ruptures, a massive hemorrhage into the abdominopelvic gross examination and histologic sections: cavity can endanger the life of the mother. Unfortunately, there currently is no way to treat a tubal pregnancy that can spare the ■ The infundibulum (in-fŭn-dib ́ū -lŭm; funnel) is the free, developing embryo. funnel-shaped, lateral margin of the uterine tube. Its numerous individual fingerlike folds are called fimbriae (fim ́brē -ē ; fringes). The fimbriae of the infundibulum are not attached to the ovary but enclose it at the time of ovulation. muscularis help propel the secondary oocyte, or pre-embryo if ■ The ampulla (am-pul ́lă; two-handled bottle) is the fertilization has occurred, through the uterine tube toward the expanded region medial to the infundibulum. Fertilization uterus. The serosa is the external covering the of a secondary oocyte typically occurs there. uterine tube. ■ The isthmus (is mus) ́ extends medially from the ampulla toward the lateral wall of the uterus. It forms about one- WHATW DID YOU LEARN? third of the length of the uterine tube. ●3 What are the types of ovarian follicles? ■ The uterine part (intramural part or interstitial segment) extends medially from the isthmus and is continuous with ●4 What is ovulation? the wall of the uterus. ●5 What is menarche, and when does it occur? ●6 What type of epithelium lines the uterine tubes, and what is its function? Study Tip! One way to remember the segments of the uterine tubes is as 28.2c Uterus follows: The uterus (ū ter- ́ ŭs; womb) is a pear-shaped, thick-walled muscu- lar organ within the pelvic cavity. It has a lumen (internal space) ■ The infundibulum (the only segment with an “F” in it) has the fimbriae. that connects to the uterine tubes superolaterally and to the vagina inferiorly (figure 28.7a). Normally, the uterus is angled anterosupe- ■ The ampulla is the arm of the uterine tube. riorly across the superior surface of the urinary bladder, a position ■ The isthmus is the longest. referred to as anteverted (an-te-vert ed; ́ ante = before, versio = a

■ The uterine part is in the uterus. turning). If the uterus is positioned posterosuperiorly (so that it is projecting toward the rectum), this position is called retroverted (re tr ́ ō -ver-ted). In older women, the uterus may shift from ante- verted to retroverted. The wall of the uterine tube consists of a mucosa, a mus- The uterus serves many functions. Following fertiliza- cularis, and a serosa. The mucosa is formed from a ciliated tion, the pre-embryo makes contact with the uterine lining and columnar epithelium and a layer of areolar connective tissue. implants in the inner uterine wall. The uterus then supports, The mucosa is thrown into linear folds, which reduce the size of protects, and nourishes the developing embryo/fetus by forming the uterine tube lumen. After ovulation, the cilia on the apical a vascular connection that later develops into the placenta. The surface of the epithelial cells of both the infundibulum and the uterus ejects the fetus at birth after maternal oxytocin levels ampulla begin to beat in the direction of the uterus. This beat- increase to initiate the uterine contractions of labor. If a sec- ing causes a slight current in the fluid within the uterine tube ondary oocyte is not fertilized, the muscular wall of the uterus lumen, drawing the ovulated oocyte into the uterine tube and contracts and sheds its inner lining as menses. moving it toward the uterus. The uterus is partitioned into the following regions: The muscularis is composed of an inner circular layer and an outer longitudinal layer of smooth muscle cells. The muscular ■ The fundus (fŭn ́dŭs) is the broad, curved superior region layer increases in relative thickness as the uterine tube approaches extending between the lateral attachments of the uterine the lateral wall of the uterus. Some peristaltic contractions in the tubes.

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Muscularis

Lumen of Mucosa uterine tube Simple ciliated columnar epithelium

LM 35x

(b) Uterine tube

Suspensory Ovarian ligament of ovary blood vessels LM 400x Uterine tube Uterine part

Isthmus Ovarian Fundus Lumen Uterine ligament of uterus of uterus Ampulla tube Infundibulum

Fimbriae Mesosalpinx Ovary

Body of uterus

Endometrium Round Broad ligament Wall of ligament uterus Isthmus Uterine blood vessels Internal os

Cervical canal Cervix Ureter External os Lumen of uterus

Epithelium Transverse cervical ligament

Vagina Functional Uterine layer glands

(a) Posterior view Basal layer Figure 28.7 Uterine Tubes and the Uterus. The uterine tubes are paired passageways that capture the ovulated secondary oocyte, provide the Myometrium site for fertilization, and transport the oocyte to the uterus. (a) The relationship between a uterine tube and the uterus is shown LM 45x in a posterior view (left) and a partially cut-away diagram (right). (b) A photomicrograph shows a cross section of the uterine tube. (c) Uterus (c) A photomicrograph shows the layers of the endometrium and part of the myometrium in the wall of the uterus.

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CLINICAL VIEW Cervical Cancer 2. Epithelial cells are scraped from the edge of the cervix and placed (smeared) on a microscope slide. Cervical cancer is one of the most common malignancies of the female 3. The slide is sent to a lab, where a cytologist stains the cells reproductive system. It is estimated that over 12,000 new cases of invasive and examines them under the microscope, noting any abnormal cervical cancer and four times that many noninvasive cervical cancer cases cellular development (termed dysplasia). are diagnosed each year. Approximately 4000 women die from cervical If dysplastic cells are detected, the health-care professional will likely cancer annually. Risk factors for cervical cancer include increased age, HIV request a follow-up Pap smear and possibly even a biopsy. Sometimes, infection, and low socioeconomic status. However, the most important risk dysplastic cells are a result of irritation, infection, or some undeter- factor is previous human papillomavirus (HPV) infection. Some classes of mined cause, and are not cancerous. But if advanced dysplasia is seen, HPV are considered “high risk” because they are frequently associated with most physicians immediately recommend a biopsy of the cervix, and genital and anal cancers in men and women and are sexually transmitted. may even insist on HPV testing. If cervical cancer is present, surgery The Papanicolaou (Pap) smear has become a very effective method is indicated. To treat a cancer that is localized, a portion of the cervix of detecting cervical cancer in its early and curable stage. The test is may be removed, a procedure known as a cone biopsy. In the case of done in the doctor’s office as follows: invasive cancer, removal of the entire uterus, called a hysterectomy (his-ter-ek tó ¯-me¯ ; hystera = womb), is indicated. Researchers recently 1. The health-care professional inserts a metal or plastic have developed vaccines (Gardasil and Cervarix) for the most common instrument called a speculum (spek u ́¯-lu˘m; mirror) into the vagina to keep the vagina open in order to examine the cervix. types of HPV that cause cervical cancer. The vaccines are targeted for women and girls between the ages of 9 and 26 years.

Epithelial cells Normal cells Dysplastic cells

LM 140x LM 160x

Normal Pap smear. Abnormal Pap smear.

■ The major part of the uterus is its middle region, called the Support of the Uterus body, which is composed of a thick wall of smooth muscle. Several structures support the uterus. The muscles of the pelvic ■ A narrow, constricted inferior region of the body that is floor (pelvic diaphragm and ) (see figure superior to the cervix is called the isthmus. 11.15 ) hold the uterus and vagina in place and help resist intra- ■ The cervix is the narrow inferior portion of the uterus that abdominal pressure exerted inferiorly on the pelvis. The round projects into the vagina. (figure 28.7) of the uterus extend from the lateral sides of the uterus, through the inguinal canal and attach to the labia Within the cervix is a narrow channel called the cervical majora. These ligaments help keep the uterus in an anteverted canal, which connects to the vagina inferiorly. The superior open- position. The transverse cervical ligaments (or cardinal liga- ing of this canal is the internal os (os = mouth). The inferior ments) run from the sides of the cervix and superior vagina later- opening of the cervix into the lumen of the vagina is the external ally to the pelvic wall. They help restrict inferior movements of os. The external os is covered with nonkeratinized stratified squa- the uterus. The uterosacral ligaments (or sacrocervical ligaments; mous epithelium. The cervix contains mucin-secreting glands that not shown in figure 28.7) connect the inferior portion of the uterus help form a thick mucus plug at the external os. This mucus plug posteriorly to the sacrum. is suspected to be a physical barrier that prevents pathogens from Many of these ligaments travel between the folds of the broad invading the uterus from the vagina. The mucus plug thins con- ligament. Weakness in either the muscles or these liga- siderably around the time of ovulation, so sperm may more easily ments can lead to prolapse (prō -laps ; ́ prolapsus = a failing) of the enter the uterus. uterus, in which the uterus starts to protrude through the vagina.

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Despite its name, the broad ligament is not a strong support for the stratum functionalis (fŭnk-shŭn-ăl ́is). Beginning at puberty, the func- uterus, but rather a peritoneal drape over the uterus. tional layer grows from the basal layer under the influence of estrogen and progesterone secreted from the ovarian follicles. If fertilization and Blood Supply implantation do not occur, this lining is shed as menses. Each internal iliac artery extends a branch called a uterine artery through the broad ligament to the lateral wall of the uterus (see Uterine (Menstrual) Cycle and Menstruation figure 28.7). Numerous smaller branches from the uterine artery The cyclical changes in the endometrial lining occur under the then penetrate the muscular wall of the uterus and further diverge influence of estrogen and progesterone secreted by the ovary. The into arcuate arteries. Thereafter, each arcuate artery gives rise to uterine cycle (or menstrual cycle) consists of three distinct phases smaller vessels, called radial arteries, which extend into the inner- of endometrium development: the menstrual phase, proliferative most layer (endometrium) of the uterus. Here they branch into phase, and secretory phase (see figure 28.6, bottom). spiral arteries, which swirl throughout the endometrium, extend- The menstrual (men stroo- ́ ăl; menstrualis = monthly) phase ing between and throughout the uterine glands (described below) occurs approximately during days 1–5 of the cycle. This phase is toward the mucosal surface. marked by sloughing of the functional layer and lasts through the period of menstrual bleeding. The proliferative (prō -lif er- ́ ă-tiv; Wall of the Uterus proles = offspring, fero = to bear) phase follows, spanning approxi- The uterine wall is composed of three concentric tunics: the peri- mately days 6–14. The initial development of the functional layer of metrium, myometrium, and endometrium (figure 28.7). The outer the endometrium overlaps the time of follicle growth and estrogen tunic of most of the uterus is a serosa called the perimetrium (per-i- secretion by the ovary. The last phase is the secretory (se-krēt ́ĕ-rē, mē tr ́ ē -ŭm; metra = uterus). The perimetrium is continuous with the sē ́krĕ-tō r-ē) phase, which occurs between approximately days 15–28. broad ligament. The myometrium (mı̄ ́ō -mē tr ́ ē -ŭm; mys = muscle) During the secretory phase, increased progesterone secretion from the is the thick, middle tunic of the uterine wall formed from three corpus luteum results in increased vascularization and development intertwining layers of smooth muscle. In the nonpregnant uterus, of uterine glands. If the secondary oocyte is not fertilized, the corpus the muscle cells are less than 0.25 millimeter in length. During the luteum degenerates, and the progesterone level drops dramatically. course of a pregnancy, smooth muscle cells increase both in size Without progesterone, the functional layer lining sloughs off, and the (hypertrophy; hı̄-per tr ́ ō -fē) and in number (hyperplasia; hi-per- next uterine cycle begins with the menstrual phase. plā zh ́ ē -ă). Some cells may exceed 5 millimeter in length by the Table 28.3 compares the uterine cycle with the ovar- end of gestation. The innermost tunic of the uterus, called the endo- ian cycle discussed previously, and table 28.4 summarizes the metrium (en ́dō -mē tr ́ ē -ŭm), is an intricate mucosa composed of a hormones that influence the ovarian and uterine cycles. The day simple columnar epithelium and an underlying lamina propria. The ranges listed on figure 28.6 and table 28.3 assume that the woman lamina propria is filled with compound tubular glands (also called has a 28-day cycle, meaning she ovulates at day 14 and has a men- uterine glands), which enlarge during the uterine cycle. strual period every 28 days. If a woman has a longer cycle (say, Two distinct layers form the endometrium. The deeper layer is she menstruates about every 35 days), her menstrual phase and/or the basal layer, also called the stratum basalis (bā -s ā ́lis). The basal her proliferative phase is longer than average. Typically, a woman layer is immediately adjacent to the myometrium, and is a permanent ovulates 14 days before menstruation, so the secretory phase day layer that undergoes few changes during each uterine cycle. The more ranges do not vary as much. superficial of the two endometrial layers is the functional layer, or WHAT DO YOU THINK?

●2 What factors could influence the length and timing of a woman’s monthly uterine cycle? CLINICAL VIEW 28.2d Vagina Endometriosis The vagina (vă-jı̄ n ́ ă) is a thick-walled, fibromuscular tube that Endometriosis (en ́do¯-me¯ -tre¯ -o¯ sis) ́ occurs when part of the forms the inferiormost region of the female reproductive tract and endometrium is displaced onto the external surface of organs measures about 10 centimeters in length in an adult female (see within the . Scientists think that during the figure 28.2). The vagina connects the uterus with the outside of regular uterine (menstrual) cycle of some women, a small amount of endometrium may be expelled from the uterine tubes and become implanted on the surface of the ovaries, uterine tubes, Table 28.3 Comparison of Ovarian and Uterine urinary bladder, and intestines. If this displaced endometrium Cycle Phases remains viable, it responds to hormone stimulation during each Day1 Ovarian Cycle Uterine Cycle menstrual growth phase. Unfortunately, at the end of the monthly Phase Phase cycle, this displaced endometrium cannot slough and be expelled. 1–5 Menstrual phase Thus, the ensuing hemorrhage and breakdown of the displaced Follicular phase endometrium cause considerable pain and eventually scarring 6–13 Proliferative phase that often leads to deformities of the uterine tubes. Treatments 14 Ovulation include the use of hormones designed to retard the growth and 15–28 Luteal phase Secretory phase cycling of the displaced endometriotic tissue, as well as surgical removal of the ectopic endometrium. 1This table assumes a 28-day cycle between menstrual periods. If a woman has a longer or shorter cycle, the day ranges for the follicular, menstrual, and proliferative phases will vary.

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Table 28.4 Infl uence of Hormones on the Ovarian and Uterine Cycles Hormone Primary Source of Hormone Effects Gonadotropin-releasing hormone (GnRH) Hypothalamus Stimulates anterior pituitary to produce and secrete FSH and LH Follicle-stimulating hormone (FSH) Anterior pituitary Stimulates development and maturation of ovarian follicles Luteinizing hormone (LH) Anterior pituitary Stimulates ovulation (when there is a peak in LH) Estrogen Ovarian follicles (before ovulation), corpus Initiates and maintains growth of the functional layer of the luteum (after ovulation), or placenta (during endometrium pregnancy) Progesterone Corpus luteum or placenta (during Primary hormone responsible for functional layer growth pregnancy) after ovulation; causes increase in blood vessel distribution, size, and nutrient production Inhibin Ovarian follicles Inhibits FSH secretion, so as to prevent excessive follicular development

the body anteroventrally, and thus functions as the birth canal. arteries, and venous drainage is via vaginal veins. The lumen of The vagina is also the copulatory organ of the female, as it the vagina is flattened anteroposteriorly. The vagina’s relatively receives the penis during intercourse, and it serves as the pas- thin, distensible wall consists of three tunics: an inner mucosa, a sageway for menstruation. middle muscularis, and an outer . The vaginal wall is heavily invested with both blood vessels The mucosa consists of a nonkeratinized stratified squamous and lymphatic vessels. Arterial supply comes from the and a highly vascularized lamina propria (figure 28.8).

Figure 28.8 Histology of the Vagina. The epithelial lining of the vagina in a mature female is a Nonkeratinized stratified squamous epithelium. stratified squamous epithelium Mucosa

Lamina propria

Muscularis LM 50x

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Superificial cells of the vaginal epithelium contribute to the acidic Mons pubis environment that helps prevent bacterial and other pathogenic inva- Glans of clitoris Prepuce sion. During each menstrual phase, large numbers of and granulocytes invade the lamina propria to help prevent infec- tion during menstruation. The inferior region of the vaginal mucosa contains numerous transverse folds, or rugae. Near the external opening of the vagina, called the vaginal orifice, these mucosal folds project into the lumen to form a vascularized, membranous Urethral opening barrier called the (hı̄ men; ́ membrane). The hymen typically Vestibule is perforated during the first instance of , but also Vaginal orifice may be perforated by tampon use, medical exams, or very strenuous Openings for greater vestibular glands physical activity. The muscularis of the vagina has both outer and inner layers of smooth muscle. The outer layer is composed of bundles of longi- tudinal smooth muscle cells that are continuous with correspond- ing muscle cells in the myometrium. The smooth muscle cells of Anus the inner circular layer are interwoven with the outer longitudinal muscle fibers at the point where the two muscle layers meet. Near the vaginal orifice are some fibers of the muscu- laris layer that cause partial narrowing of the vaginal orifice. The adventitia contains some inner elastic fibers and an outer layer of areolar connective tissue. Figure 28.9 28.2e External Genitalia Female External Genitalia. Inferior view of the external genitalia, The external sex organs of the female are termed the external illustrating the urethral opening and the vaginal orifice, which are genitalia or (vŭl v ́ ă; a covering) (figure 28.9).s The mon within the vestibule and bounded by the labia minora. (monz; mountain) pubis is an expanse of skin and subcutaneous connective tissue immediately anterior to the pubic symphysis. The mons pubis is covered with pubic hair in postpubescent females. are tubuloacinar glands that secrete mucin, which forms mucus to The labia majora (lā ́b ē -ă mă-jo˘r ́ă; sing., labium majus; labium = act as a lubricant for the vagina. Secretion increases during sexual , majus = larger) are paired, thickened folds of skin and con- intercourse, when additional lubrication is needed. These secretory nective tissue. The labia majora are homologous to the scrotum of structures are homologous to the male bulbourethral glands. the male. In adulthood, their outer surface is covered with coarse The clitoris (klit ́ō -ris) is a small erectile body, usually less pubic hair; they contain numerous sweat and sebaceous glands. than 2 centimeters in length, located at the anterior regions of the The labia minora (mı̄-no˘r ́ă; sing., labium minus; minus = smaller) labia minora. It is homologous to the penis of the male. Two small are paired folds immediately internal to the labia majora. They erectile bodies called corpora cavernosa form the body of the cli- are devoid of hair and contain a highly vascular layer of areolar toris. Extending from each of these bodies posteriorly are elongated connective tissue. Sebaceous glands are located in these folds, as masses, each called the crus (kroos) of the clitoris, which attach are numerous melanocytes, resulting in enhanced pigmentation of to the pubic arch. Capping the body of the clitoris is the glans the folds. (glanz; acorn). The many specialized sensory nerve receptors The space between the labia minora is called the vestibule. housed in the clitoris provide pleasure to the female during sexual Within the vestibule are the urethral opening and the vaginal ori- intercourse. The prepuce (prē poos; ́ ) is an external fold of fice. On either side of the vaginal orifice is an erectile body called the labia minora that forms a hoodlike covering over the clitoris. the bulb of the vestibule (see figure 27.10), which becomes erect and increases in sensitivity during sexual intercourse. A pair of 28.2f Mammary Glands greater vestibular glands (previously called glands of Bartholin) Each , or breast, is located within the anterior tho- are housed within the posterolateral walls of the vestibule. These racic wall and is composed of a compound tubuloalveolar exocrine

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CLINICAL VIEW: In Depth Contraception Methods (nursing a baby) can prevent ovulation and menstruation for several to many months after childbirth if a woman nurses her child con- The term contraception (kon-tra˘-sep shun) ́ refers to birth control, or stantly (i.e., much more than five times a day!). The frequent lactation the prevention of pregnancy. A wide range of birth control methods sends signals to the hypothalamus to prevent FSH and LH from being are available, and they have varying degrees of effectiveness. secreted, thus preventing ovulation. Many U.S. women do not nurse a child constantly, so lactation is not a reliable birth control method for them. If Abstinence (ab sti-nens; ́ abstineo = to hold back) means refraining a woman is lactating, she should always use another form of birth control from sexual intercourse. Abstinence (when practiced correctly) is the as well, because she will not know when her ovulation cycle begins again. only 100% proven way not to become pregnant. Barrier methods of birth control use a physical barrier to prevent Natural (also known as the rhythm method) requires sperm from reaching the uterine tubes. Barrier methods include the avoiding sexual intercourse during the time when a woman is ovulat- following: ing. Because sperm can live for several days in the female reproduc- tive tract, it is best to avoid intercourse both a few days prior and a ■ Condoms, when used properly, collect the sperm and prevent few days after ovulating. The rhythm method requires that a woman them from entering the female reproductive tract. They are know when she is ovulating, which may be difficult to determine also the only birth control method that helps protect against consistently. As a result, this method has a high failure rate (25%). sexually transmitted viruses and diseases, such as human

(a) Condoms (b) Spermicidal foams (c) Diaphragm

Each ductus deferens is tied off and cut

Uterine tubes are tied off and cut

(d) Oral contraceptive (e) Intrauterine device (IUD) (f) Tubal ligation (g) Contraception includes barrier, chemical, and surgical methods.

gland (figure 28.10). The gland’s complex secretory product (nŭl-ip ́ă-rŭs; nullus = none, pario = to bear) woman (a woman who (called ) contains proteins, fats, and a sugar to provide has never given birth), the is rosy or light brown in color. nutrition to . In a parous (par ́ŭs) woman (a woman who has given birth), the The (nip ́l; beak) is a cylindrical projection on the areola may change to a darker rose or brown color. center of the breast. It contains multiple tiny openings of the excre- Internally, the are supported by fibrous connective tory ducts that transport breast milk. The areola (ă-rē ́ō -lă; small bands called suspensory ligaments. These thin bands extend area) is the pigmented, rosy or brownish ring of skin around the from the skin and attach to the deep overlying the pectoralis nipple. Its surface often appears uneven and grainy due to the major muscle. Thus, the breast and the pectoralis major muscle are numerous sebaceous glands, called areolar glands, immediately structurally linked. internal to the surface. The color of the areola may vary, depending The mammary glands are subdivided into lobes, which are upon whether or not a woman has given birth. In a nulliparous further subdivided into smaller compartments called lobules. Lobules

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papillomavirus, herpes, and HIV. Condoms for males fit snugly ■ Estrogen/progestin (pro¯-jes tin;́ pro = before, gestation) on the erect penis, while vaginal condoms are placed in the patches are alternatives to the daily oral contraceptive. vagina prior to sexual intercourse. The typical use failure rate A patch placed on the body delivers a regular amount of for condoms is about 14–15%. estrogen/progestin through the skin (transdermally). The patch ■ Spermicidal foams and gels are chemical barrier methods is replaced each week. The typical use failure rate is 1%. that kill sperm before they travel to the uterine tubes. They ■ Implanted/injected progestins help prevent pregnancy are inserted into the vagina and/or placed on the penis by preventing ovulation and thickening the mucus around prior to sexual intercourse. Foams and gels are not the most the cervix (thus creating a slight physical barrier to the effective method of birth control (alone the failure rate is sperm). Medroxyprogesterone (Depo-Provera) is an injectable typically 26%); rather, they should be used in conjunction contraceptive given once every 3 months, while etonogestrel with a physical barrier method. (Implanon) is an implantable contraceptive that lasts for up ■ Diaphragms and cervical caps are circular, rubbery structures to 3 years. The drawback is that ovulation may not occur for that are inserted into the vagina and placed over the cervix many months after stopping their use. The typical use failure prior to sexual intercourse. Spermicidal gel is used around the rate for these products is 0.3%. edges to help prevent sperm from entering the cervix. Some ■ A vaginal ring is a flexible polymer ring that contains women find it difficult to correctly place the diaphragm or etonogestrel and (NuvaRing) and is placed in cervical cap, and incorrect placement can result in pregnancy. the vagina. The hormones are slowly absorbed directly by The failure rate for these products is high, typically 20% for the reproductive organs. One ring lasts 3 weeks; it is diaphragms and up to 40% for cervical caps. removed for a week and menstruation occurs. Typical use failure rate is 8%. Intrauterine devices (IUDs) are T-shaped, flexible plastic structures ■ Morning-after pills containing levonorgestrel (e.g., Preven inserted into the uterus by a health-care provider. Once in place, the or Plan B One-Step) must be taken within 48 to 72 hours IUD prevents fertilization from occurring. The IUD may contain copper, after having unprotected intercourse and is most effective a synthetic progestin, or levonorgestrel. IUDs containing copper are when taken within 24 hours. These pills work by inhibiting effective for up to 10 years; those with progestin (e.g., Progestasert) ovulation, altering the menstrual cycle to delay ovulation, or must be replaced every year; and those containing levonorgestrel (e.g., irritating the uterine lining to prevent implantation. Mirena) are effective for 5 years . Although few women in North America ■ Mifepristone (Mifiprex in the United States; RU-486 in use IUDs, their failure rate typically is low (2%). Europe) was approved in 2000 by the U.S. Food and Drug Chemical methods of birth control are very effective if used properly. Administration for use during the first 7 weeks of pregnancy. They include the following: Mifepristone blocks progesterone receptors, so progesterone cannot attach to these receptors and thereby maintain ■ Oral contraceptives, commonly called birth control pills, come a pregnancy. When taken with a prostaglandin drug, in packets varying from 21 to 91 days. These pills contain low mifepristone induces a miscarriage. Mifepristone’s existence levels of estrogen and/or progestins. Some packets include a is very politically charged, with both sides of the abortion week of non-hormone-containing pills, during which circulating debate arguing for or against its use. levels of estrogen and progestins drop, and menstruation occurs. (Note: Progesterone is one type of progestin.) The low The surgical methods of contraception are tubal ligation for females levels of estrogen and progestins prevent the LH “spike” needed and vasectomy (va-sek tó ¯-me¯ ) for males. In a tubal ligation, both for ovulation. Thus, oral contraceptives prevent ovulation. uterine tubes are cut, and the ends are clipped, tied, or cauterized Typically, menstrual flow is much lighter when a woman takes shut. Thus, tubal ligation prevents both sperm from reaching the oral contraceptives because the circulating levels of hormones oocyte and the oocyte from reaching the uterus. A vasectomy is an were low to begin with, so the uterine lining does not build outpatient procedure whereby each ductus deferens is cut and the ends up much. Oral contraceptives require a woman to take a pill tied, clipped, or cauterized shut. Sperm cannot leave the testis and a day, at about the same time each day. If she misses one or thus are not ejaculated. Both surgeries are very effective birth control more days of pills, ovulation may occur. Typical use failure rate methods, but they are meant to be permanent and irreversible, so they depends upon the product and is between 0.1% and 7%. are not considered options for people who wish to have more children.

contain secretory units termed alveoli that produce milk in the lactat- woman starts to produce breast milk when she has recently given ing female. Alveoli become more numerous and larger during preg- birth. When a woman is pregnant, the levels of estrogen, proges- nancy. Tiny ducts drain milk from the alveoli and lobules. The tiny terone, and prolactin rise dramatically. Recall from chapter 20 ducts of the lobules merge and form 10 to 20 larger channels called that the hormone prolactin is produced in the anterior pituitary lactiferous (lak-tif er- ́ ŭs; lact = milk, fero = to bear) ducts. A lactiferous and is responsible for milk production. Thus, when the amount of duct drains breast milk from a single lobe. As each prolactin increases, the mammary gland grows and forms more approaches the nipple, its lumen expands to form a lactiferous sinus, expanded and numerous alveoli. a space where milk is stored prior to release from the nipple. While prolactin stimulates production of breast milk, the hor- Breast milk is released by a process called lactation (lak- mone oxytocin is responsible for milk ejection. Recall from chapter 20 tā sh ́ ŭn; lactatio = to suckle), which occurs in response to a that oxytocin is secreted by the hypothalamus and stored in the poste- complex sequence of internal and external stimuli. Normally, a rior lobe of the pituitary, and is also responsible for uterine contractions

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Suspensory ligaments

Adipose tissue Suspensory ligaments Intercostal muscles

Pectoralis minor Lactiferous Pectoralis major sinus

Lobe Lobe Areolar gland Deep fascia Lactiferous sinus Nipple Alveoli Nipple Alveoli Areola Lactiferous ducts

Lobule Lobule

Lactiferous ducts (a) Anteromedial view (b) Sagittal view

Figure 28.10 Mammary Glands. The mammary glands are composed of glandular tissue and a variable amount of fat. (a) An anterior view is partially cut away to reveal internal structures. (b) A diagrammatic sagittal section of a mammary gland shows the distribution of alveoli within lobules and the extension of ducts to the nipple.

CLINICAL VIEW Breast Cancer be examined to see if the malignancy has spread. If it has, treatment depends upon the stage of the malignancy, but usually includes surgery Breast cancer affects approximately 1 in every 8 women in the United and/or chemotherapy. Patients often take drugs that block the effect States, and it also occurs in males, although infrequently. The incidence of the estrogen receptor (e.g., tamoxifen [Nolvadex] and raloxifene of breast cancer is rare before age 20. Then it rises steadily to peak at [Evista]) for years after the surgery. about the age of menopause. Some well-documented risk factors for breast cancer include: maternal relatives with breast cancer, longer repro- ductive span (early menarche coupled with delayed menopause), obesity, nulliparity (never having been pregnant), late age at first pregnancy, and the presence of in specific breast cancer (BRCA1 and BRCA2). Except for the genetic influence, all of the risk factors are related to increased exposure to estrogen over a long period of time. Breast cancers arise from the duct epithelium, not the actual milk- producing cells. Monthly self-examination has proved to be one of the most important means of early detection of breast malignancies. Mammography, which is an x-ray of the breast that can detect small areas of increased tissue density, can identify many small malignan- Tumor cies that are not yet palpable in a self-examination. Recommendations vary, but most physicians agree that women over the age of 40 should have a mammogram done every 1 to 2 years. Women with a family history of breast cancer should consider regular mammography before the age of 40. Because the lymph drainage from the breast goes predominately to the axilla, the axillary lymph nodes on the side with the cancer must Mammogram showing a malignant tumor.

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during labor. In response to a stimulus, such as a baby crying or suck- 3. Outline the male reproductive duct system, and explain the ing the nipple, oxytocin is released, and milk is ejected from the function of each component. nipple. As milk drains from the alveoli, increased levels of prolactin 4. Describe the anatomy and function of the male accessory are released so the breast can produce more milk. Once a baby stops reproductive organs. nursing, the levels of oxytocin drop, and milk ejection ceases. 5. List the components of the penis. During the first few weeks of breast-feeding, the mother may experience uterine contractions called afterpains, which are caused In the male, the primary sex organs are the testes (tes t ́ ē z; by the increased levels of oxytocin in her bloodstream. These uter- sing., testis). The accessory reproductive organs include a complex ine contractions help shrink the uterus to its prepregnancy size. set of ducts and tubules leading from the testes to the penis, a Afterpains typically become less noticeable and cease a few weeks group of male accessory glands, and the penis, which is the organ after birth, by which time the uterus has shrunk considerably. of copulation (figure 28.11).

WHATW DID YOU LEARN? 28.3a Scrotum ●7 Identify and describe the ligaments that support the uterus and The ideal temperature for producing and storing sperm is about hold it in place. 3° Celsius lower than internal body temperature. The scrotum ●8 What name is given to the innermost tunic of the uterus? What (skrō t ́ ŭm), which is a skin-covered sac between the thighs, pro- are the two distinct layers that form this tunic? vides the cooler environment needed for normal sperm develop- ●9 What mammary gland structures produce and drain milk from ment and maturation (figure 28.12). The scrotum is homologous each lobe? to the labia majora in the female. Externally, the scrotum contains a distinct, ridgelike seam at its midline, called the raphe (rā ́f ē ; rhaphe = seam). The raphe per- 28.3 Anatomy of the Male sists in an anterior direction along the inferior surface of the penis Reproductive System and in a posterior direction to the anus. The wall of the scrotum is composed of an external layer of skin, a thin layer of superfi- Learning Objectives: cial fascia immediately internal to the skin, and a layer of smooth 1. Describe the gross and microscopic anatomy of the testes. muscle, the (dar tos; ́ skinned) muscle, immediately internal 2. Explain both and . to the fascia.

Ureters

Urinary bladder

Pubic symphysis Ampulla of ductus deferens Ductus deferens Seminal vesicle Urogenital diaphragm gland

Bulbourethral gland

Urethra Anus Penis

Glans Testis

Scrotum

Figure 28.11 Male Pelvic Region. A diagrammatic sagittal section shows the locations and relationships of the male pelvic structures.

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Testicular artery Testicular vein

Ureter Penis Urinary bladder Inguinal ligament

Ductus Superficial deferens inguinal ring

Pampiniform Structures plexus Spermatic cord within spermatic cord Testicular artery Testicular nerve External spermatic fascia within Epididymis cremasteric fascia Layers of spermatic Internal spermatic fascia cord wall Testis Dartos muscle Raphe

Scrotum

Penis Superficial inguinal ring Inguinal ligament

Ductus deferens Spermatic cord Testicular nerve Structures Cremaster muscle within within Testicular artery cremasteric fascia spermatic and pampiniform cord plexus

Epididymis

Testis Testis

Raphe

Figure 28.12 Scrotum and Testes. A diagram and a cadaver photo show the scrotum, a skin-covered sac that houses the testes, in anterior view. A multilayered spermatic cord houses the blood vessels, nerves, and a sperm-carrying duct (ductus deferens) for each testis.

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Spermatic cord

Blood vessels and nerves

Ductus deferens

Head of epididymis Duct of epididymis Interstitial cells Seminiferous Efferent ductule tubule Tubule lumen Septum (housing ) Sustentacular Lobule cells Sperm cells

Visceral layer of Body of epididymis

Parietal layer of Spermatogonia tunica vaginalis

Tunica albuginea LM 250x

(b) Seminiferous tubule, cross section Tail of epididymis

(a) Testis Figure 28.13 Testes and Seminiferous Tubules. (a) The gross anatomy of a testis is shown diagrammatically in a cut-away, partial sagittal section. (b) A photomicrograph reveals a cross section of a seminiferous tubule in the testis.

When the testes are exposed to elevated temperatures, the ■ An external spermatic fascia is formed from the dartos muscle relaxes, which unwrinkles the skin of the scrotum aponeurosis of the external oblique muscle. and allows the testes to move further away from the body. This Within the spermatic cord is a singular testicular artery that inferior movement away from the body cools the testes. At the is a direct branch from the abdominal aorta. The testicular artery same time, another muscle (the cremaster muscle) also relaxes to is surrounded by a plexus of veins called the pampiniform (pam- allow the testes to move inferiorly away from the body. The oppo- pin ́i-form; pampinus = tendril, forma = form) plexus. This venous site occurs if the testes are exposed to cold. In this case, the dartos plexus is a means to provide thermoregulation by pre-cooling and cremaster muscles contract, pulling the testes and scrotum arterial blood prior to reaching the testes. Autonomic nerves travel closer to the body to conserve heat. with these vessels and innervate the testis. 28.3b Spermatic Cord 28.3c Testes The blood vessels and nerves to the testis travel from within the In the adult human male, each testis is an oval organ housed with- to the scrotum in a multilayered structure called the in the scrotum (figure 28.12). Each weighs approximately 10–12 spermatic cord (figure 28.12; see figure 28.13a). The spermatic grams, and displays average dimensions of 4 centimeters (cm) in cord originates in the inguinal canal, a tubelike passageway length, 2 cm in width, and 2.5 cm in anteroposterior diameter. The through the inferior . The spermatic cord wall con- testes produce sperm and androgens (male sex hormones). sists of three layers: Each testis is covered both anteriorly and laterally by a serous ■ An internal spermatic fascia is formed from fascia deep to membrane, the tunica vaginalis (văj-in-ăl ı̆́ s; ensheathing). This the abdominal muscles. membrane is derived from the peritoneum of the abdominal cav- ■ The cremaster (krē -mas ter; ́ a suspender) muscle and ity. The tunica vaginalis has an outer parietal layer and an inner cremasteric fascia are formed from muscle fiber extensions visceral layer that are separated by serous fluid. A thick, whitish, of the internal oblique muscle and its aponeurosis, fibrous capsule called the tunica albuginea covers the testis and respectively. lies immediately deep to the visceral layer of the tunica vaginalis

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(figure 28.13a). At the posterior margin of the testis, the tunica lie near the base of the seminiferous tubule, surrounded by the albuginea thickens and projects into the interior of the organ as cytoplasm of sustentacular cells. To produce sperm, spermato- the mediastinum testis. Blood vessels, a system of ducts, lymph gonia first divide by mitosis. One of the cells produced is a new vessels, and some nerve fibers enter or leave each testis through (a new ), to ensure that the numbers the mediastinum testis. of spermatogonia never become depleted, and the other cell is a The tunica albuginea projects internally into the testis and “committed cell” called primary . Primary sper- forms delicate connective tissue septa, which subdivide the inter- matocytes are diploid and an exact copy of spermatogonia. It is the nal space into about 250 separate lobules. Each lobule contains primary that undergo meiosis. up to four extremely convoluted, thin and elongated seminiferous When a primary spermatocyte undergoes meiosis I, the two (sem ́i-nif er- ́ ŭs; semen = seed, fero = to carry) tubules. The seminif- cells produced are called secondary spermatocytes. Secondary erous tubules contain two types of cells: (1) a group of nondividing spermatocytes are haploid, meaning they have 23 chromosomes support cells called the sustentacular (sŭs-ten-tak ́ū -lăr; sustento = to only. These cells remain surrounded by the sustentacular cells, but hold upright) (Sertoli or nurse) cells, and (2) a population of dividing move relatively closer to the lumen of the seminiferous tubule (as germ cells that continuously produce sperm beginning at puberty. opposed to the base of the seminiferous tubule). The sustentacular cells assist with sperm development. Secondary spermatocytes complete meiosis (go through These cells provide a protective environment for the developing meiosis II) and form spermatids (sper m ́ ă-tid). A is sperm, and their cytoplasm helps nourish the developing sperm a haploid cell and is surrounded by the sustentacular cell, very (figure 28.13b). In addition, the sustentacular cells will release the near to the lumen of the seminiferous tubule. The spermatids still hormone inhibin when sperm count is high. Inhibin inhibits FSH have a circular appearance, rather than the sleek shape of mature secretion, and thus regulates sperm production. (Conversely, when sperm. sperm count declines, inhibin secretion decreases.) During the final stage of spermatogenesis, a process called The sustentacular cells are secured together by tight junc- spermiogenesis, the newly formed spermatids differentiate to tions, which form a blood-testis barrier that is similar to the anatomically mature spermatozoa (sing., ; sper m ́ ă- blood-brain barrier. The blood-testis barrier helps protect develop- to-zo on) ́ or sperm (figure 28.14b). During spermiogenesis, the ing sperm from materials in the bloodstream. It also protects the spermatid sheds its excess cytoplasm, and the nucleus elongates. sperm from the body’s leukocytes, which may perceive the sperm A structure called the acrosome (ak r ́ ō -sō m; akros = tip, soma = as foreign since they have different numbers and body) cap forms over the nucleus. This acrosome cap contains arrangements from the male’s other body cells. digestive enzymes that help penetrate the secondary oocyte for The spaces surrounding the seminiferous tubules are called fertilization. As the spermatid elongates, a tail (flagellum) forms interstitial spaces. Within these spaces reside the interstitial cells from the organized microtubules. The tail attaches to a midpiece (or Leydig cells). Luteinizing hormone stimulates the interstitial (neck) region containing mitochondria and a centriole. These mito- cells to produce hormones called androgens (an ́drō -jen; andros = chondria provide the energy to move the tail. male human). There are several types of androgens, the most com- Although the sperm look mature, they do not yet have all of mon one being . Although the adrenal cortex secretes a the characteristics needed to successfully travel through the female small amount of androgens, the vast majority of release reproductive tract and fertilize an oocyte. The sperm must leave the is via the interstitial cells in the testis, beginning at puberty. These seminiferous tubule through a network of ducts (described next) and hormones cause males to develop the classic characteristics of axil- reside in the epididymis for a period of time to become fully motile. lary and pubic hair, deeper voice, and sperm production. Table 28.5 summarizes the stages of spermatogenesis.

WHAT DO YOU THINK? ●3 If a male’s testes were removed, would he still be able to produce androgens? Study Tip! Development of Sperm: Spermatogenesis Use these hints to help identify the various testis cells under the microscope: and Spermiogenesis = 1. Spermatogonia are closest to the seminiferous tubule base. As Spermatogenesis (sper m ́ ă-tō -jen ́ĕ-sis; genesis origin) is the pro- spermatogenesis occurs and the cells mature, more mature cells cess of sperm development that occurs within the seminiferous are found closer to the lumen of the seminiferous tubule. Note tubule of the testis. Spermatogenesis does not begin until puberty, how close the spermatozoa are to the lumen. when significant levels of FSH and LH stimulate the testis to begin 2. Sometimes it is difficult to distinguish an entire sustentacular gamete development. cell because its cytoplasm is pale and surrounds the developing The process of spermatogenesis is shown in figure 28.14a. sperm. You can identify sustentacular cells by their nucleus, All sperm develop from primordial germ (stem) cells called sper- which is oval or flattened and usually has a prominent . matogonia (sper m ́ ă-tō -gō n ́ ē -ă; sing., spermatogonium; sperma = 3. The interstitial cells are not located within the seminiferous seed, gone = generation). Spermatogonia are diploid cells (meaning tubule but external to it, usually in clumps of three or more cells. they have 23 pairs of chromosomes for a total of 46). These cells

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Interstitial cells Interstitial space

46 1 Spermatogonium 1 Germ cells that are the origin of sperm cells are diploid cells (containing 46 chromosomes, or 23 pairs) called spermatogonia. Mitotic division Mitotic divisions of these cells produce a new germ cell and a committed cell. The committed cell is a primary spermatocyte. 46 Primary Sustentacular 46 spermatocyte cell

2 First meiotic 2 The first meiotic division begins in the diploid primary division spermatocytes. The haploid cells (containing 23 chromosomes only) produced by the first meiotic division are called secondary spermatocytes. Secondary 23 23 spermatocyte Wall of seminiferous 3 Second meiotic division 3 The second meiotic division originates with the tubule secondary spermatocytes and produces spermatids. 23 23 Spermatid 23 23 Tight junctions 23 4 23 23 23 4 The process of spermiogenesis begins with spermatids and results in morphological changes needed to form sperm that will be motile. Spermatids becoming sperm 23 23 23 23

Lumen of seminiferous Sperm cells tubule

(a) Spermatogenesis Acrosome cap Acrosome cap Spermatid Developing Developing nucleus Head acrosome cap acrosome cap Acrosome cap Nucleus Nucleus Midpiece

Mitochondria Excess cytoplasm

Mitochondria Spermatid Spermatid Mitochondria nucleus nucleus Tail Microtubules (flagellum) Developing flagellum Developing flagellum

(b) Spermiogenesis Sperm

Figure 28.14 Spermatogenesis and Spermiogenesis. (a) The processes of spermatogenesis and spermiogenesis take place within the wall of the seminiferous tubule. (b) Structural changes occur during spermiogenesis as a sperm forms from a spermatid.

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Table 28.5 Stages of Spermatogenesis Cell Type Number of Chromosomes Haploid or Diploid Action Spermatogonium 23 pairs (46) Diploid Divides by mitosis to produce a new spermatogonium and a primary spermatocyte Primary spermatocyte 23 pairs (46) Diploid Completes meiosis I to produce secondary spermatocytes Secondary spermatocyte 23 Haploid Completes meiosis II to produce spermatids Spermatid 23 Haploid Undergoes spermiogenesis, where most of its cytoplasm is shed, and a midpiece, tail, and head form Spermatozoon (sperm) 23 Haploid Leaves seminiferous tubule and matures in epididymis

WHATW DID YOU LEARN? that first enter the epididymis look like mature sperm but can’t ●10 What is the scrotum? It is homologous to what structure in the move like mature sperm. If they are expelled too soon, they lack female? the ability to be motile, which is necessary to travel through the female reproductive tract and fertilize a secondary oocyte. If sperm ●11 What is the function of the interstitial cells, and where are they located within the testis? are not ejaculated, the older sperm degenerate and are resorbed by cells lining the duct of the epididymis. ●12 Describe the process of spermatogenesis, and mention when it first occurs. Ductus Deferens When sperm leave the epididymis, they enter the ductus deferens 28.3d Ducts in the Male Reproductive System (de ̆f er-ens; ́ carry away), also called the . The ductus The left and right testes each have their own set of ducts. These deferens is a thick-walled tube that travels within the spermatic ducts store and transport sperm as they mature and pass out of the cord, through the inguinal canal, and then within the pelvic cav- male body (figure 28.15). ity before it nears the prostate gland (figure 28.15a). The wall of the ductus deferens is composed of an inner mucosa (lined with Ducts Within the Testis pseudostratified ciliated columnar epithelium), a middle mus- The rete (rē t ́ ē ; net) testis is a meshwork of interconnected channels cularis, and an outer adventitia (figure 28.15b). The muscularis in the mediastinum testis that receive sperm from the seminiferous contains three layers of smooth muscle: an inner longitudinal, tubules. The rete testis is lined by simple cuboidal epithelium with middle circular, and outer longitudinal layer. Contraction of the short microvilli covering its luminal surface. The channels of the muscularis is necessary to move sperm through the ductus defer- rete testis merge to form the efferent ductules (see figure 28.13). ens, since sperm do not exhibit motility until they are ejaculated Approximately 12–15 efferent ductules (duk tool) ́ connect from the penis. the rete testis to the epididymis. They are lined with both cili- When the ductus deferens travels through the inguinal ated columnar epithelia that gently propel the sperm toward the canal and enters the pelvic cavity, it separates from the other epididymis and nonciliated columnar epithelia that absorb excess spermatic cord components and extends posteriorly along the fluid secreted by the seminiferous tubules. The efferent ductules superolateral surface of the bladder. It then travels inferiorly and drain into the epididymis. terminates close to the region where the bladder and prostate gland meet. As the ductus deferens approaches the superoposte- Epididymis rior edge of the prostate gland, it enlarges and forms the ampulla The epididymis (ep-i-did ́i-mis; pl., epididymides; epi = upon, didy- of the ductus deferens (figure 28.15a). The ampulla of the ductus mis = twin) is a comma-shaped structure composed of an internal deferens unites with the proximal region of the seminal vesicle to duct and an external covering of connective tissue. Its head lies form the terminal portion of the reproductive duct system, called on the superior surface of the testis, while the body and tail are the ejaculatory duct. on the posterior surface of the testis (see figure 28.13a). Internally, the epididymis contains a long, convoluted duct of the epididymis, Ejaculatory Duct which is approximately 4 to 5 meters in length and lined with pseu- Each ejaculatory duct is between 1 and 2 centimeters long. The dostratified columnar epithelium that contains stereocilia (long epithelium of the ejaculatory duct is a pseudostratified ciliated microvilli) (figure 28.15c). columnar epithelium. The ejaculatory duct conducts sperm (from The epididymis stores sperm until they are fully mature the ductus deferens) and a component of seminal fluid (from the and capable of being motile. Just as a newborn has the anatomic seminal vesicle) toward the urethra. Each ejaculatory duct opens characteristics of an adult, but cannot move as an adult, the sperm into the .

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Urinary bladder Adventitia

Ureter

Mucosa

Ampulla Seminal vesicle Ejaculatory duct LM 32x Prostate gland Muscularis Prostatic urethra Mucosa (with pseudostratified Bulbourethral Membranous ciliated columnar epithelium) gland urethra Urogenital Bulb diaphragm Crus LM 500x (b) Ductus deferens Ductus deferens Corpus cavernosum Epididymis

Section of Testis duct of epididymis

Sperm in lumen of Penis Corpus duct of spongiosum epididymis

Glans LM 50x (a) Posterior view (c) Epididymis Figure 28.15 Duct System in the Male Reproductive Tract. (a) A posterior view depicts the structural components of the male reproductive ducts and accessory glands. (b) Micrographs show a cross section through the ductus deferens. (c) A micrograph shows a cross section through the epididymis.

Urethra fluid. The components of seminal fluid are produced by accessory The urethra transports semen from both ejaculatory ducts to the glands: the , the prostate gland, and the bulboure- outside of the body. Recall from chapter 27 that the urethra is sub- thral glands. divided into a prostatic (pros-tat ́ik) urethra that extends through the prostate gland (see figure 28.15), a that Seminal Vesicles travels through the urogenital diaphragm, and a spongy urethra The paired seminal vesicles are located on the posterior sur- that extends through the penis. face of the urinary bladder lateral to the ampulla of the ductus deferens (figure 28.15a). Each seminal vesicle is an elongated, 28.3e Accessory Glands hollow organ approximately 5–8 centimeters long. The wall of Recall from earlier in this chapter that the vagina has a highly each vesicle contains mucosal folds of pseudostratified columnar acidic environment to prevent bacterial growth. Sperm cannot epithelium (figure 28.16a). It is the medial (proximal) portion survive in this type of environment, so a slightly alkaline (pH 7–8) of the seminal vesicle that merges with a ductus deferens to form secretion called seminal (sem ́i-nal) fluid is needed to neutralize the ejaculatory duct. the acidity of the vagina. In addition, as the sperm travel through The seminal vesicles secrete a viscous, whitish-yellow fluid the female reproductive tract (a process that can take hours to containing fructose, prostaglandins, and bicarbonate. The fructose several days), they are nourished by nutrients within the seminal is a sugar that nourishes the sperm as they travel through the

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Seminal vesicle

Prostate gland

Mucosal folds in seminal vesicle Tubuloalveolar glands in prostate gland

LM 25x LM 80x

(a) Seminal vesicle (b) Prostate gland Figure 28.16 Seminal Vesicles and Prostate Gland. A drawing depicts the relative locations of the seminal vesicles and the prostate gland. Micrographs show sections through (a) a seminal vesicle and (b) the prostate gland.

female reproductive tract. Prostaglandins are hormonelike sub- 28.15). Each gland has a short duct that projects into the bulb stances that promote the widening and slight dilation of the exter- (base) of the penis and enters the spongy urethra. Bulbourethral nal os of the cervix, which facilitates sperm entry into the uterus. glands are tubuloalveolar glands that have a simple columnar Bicarbonate buffers the existing fluid. and pseudostratified columnar epithelium. Their secretory prod- uct is a clear, viscous mucin that forms mucus. As a component Prostate Gland of the seminal fluid, this mucus lubricates and buffers the urethra The prostate (pros t ́ ā t; one who stands before) gland is a compact, prior to . encapsulated organ that weighs about 20 grams and is shaped like a walnut, measuring approximately 2 cm by 3 cm by 4 cm. It 28.3f Semen is located immediately inferior to the bladder. The prostate gland Seminal fluid from the accessory glands combines with sperm includes submucosal glands that produce mucin and more than from the testes to make up semen (sē men; ́ seed). When released 30 tubuloalveolar glands that open directly through numerous ducts during intercourse, semen is called the ejaculate (ē -jak ́ū -lā t), and into the prostatic urethra (figure 28.16b). Together, these glands con- it normally measures about 3 to 5 milliliters in volume and con- tribute a component to the seminal fluid. tains approximately 200 to 500 million spermatozoa. In a sexually The prostate gland secretes a slightly milky fluid that is active male, the average transit time of human spermatozoa—from weakly acidic and rich in citric acid, seminalplasmin, and pros- their release into the lumen of the seminiferous tubules, passage tate-specific antigen (PSA). The citric acid is a nutrient for sperm through the duct system, and appearance in the ejaculate—is health, the seminalplasmin is an antibiotic that combats urinary about 2 weeks. Since semen is composed primarily of infections in the male, and the PSA acts as an enzyme to fluid, a male who is very active sexually may have a reduced help liquify semen following ejaculation. (Note that the slightly sperm count because there are fewer sperm to be released from acidic secretion of the prostate does not cause the seminal fluid to the epididymis; however, the total semen volume remains close to be acidic, and thus the seminal fluid still functions to neutralize normal for that individual. the acidity of the vagina.)

Bulbourethral Glands WHAT DO YOU THINK? ŭ ́ ō ū ē ́ ă Paired, pea-shaped bulbourethral (b l b - -r thr l) glands ●4 If a male has a vasectomy, is he still able to produce sperm? If so, (or Cowper glands) are located within the urogenital diaphragm what happens to those sperm? How is the composition of semen on each side of the membranous urethra (see figures 28.11 and changed in an individual who has had a vasectomy?

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CLINICAL VIEW Benign Prostatic Hyperplasia but as it progresses, urinary symptoms may develop. Untreated prostate and cancer can metastasize to other body organs. Early diagnosis and treatment of prostate cancer are vital for cure and Benign prostatic hyperplasia (BPH) is a noncancerous enlargement of long-term survival. A very effective screening tool is a digital rectal the prostate gland. BPH is a common disorder in older men; in fact, its exam, whereby a physician inserts a finger into the rectum and palpates incidence is greater than 90% for men over 80 years of age. Hormonal adjacent structures (including the prostate gland). In addition, most changes in aging males are the cause of the enlargement. physicals for men over the age of 50 now include a test for prostate- In BPH, large, discrete nodules form within the prostate and compress the specific antigen (PSA) in the blood. The PSA level in a healthy is prostatic urethra. Thus, the patient has difficulty starting and stopping typically less than 4 ng/mL . An elevated PSA level can indicate either a stream of urine, and often complains of nocturia (excessive urinating benign prostatic hyperplasia or prostate cancer. A needle biopsy of at night), polyuria (more-frequent urination), and dysuria (painful uri- the prostate tissue can confirm the diagnosis of cancer. nation). Some drug regimens help inhibit hormones that cause prostate Several treatment options are available, depending on the stage of enlargement, but when medications are no longer effective, surgical the cancer. For earlier stages of the disease, radiation therapy may be removal of the prostatic enlargement is indicated. The most commonly beneficial—either traditional external-beam radiation or interstitial performed surgical procedure is called a TURP (transurethral resection radiotherapy, in which radioactive palladium or iodine “seeds” are per- of the prostate), in which an instrument called a resectoscope (re¯ -sek tó ¯- manently implanted in the prostate. For patients with a more aggressive sko¯p) is inserted into the urethra to cut away the problematic enlargement. cancer, the entire prostate and some surrounding structures are surgi- Prostate cancer is one of the most common malignancies among men cally removed, a procedure called a radical . No matter over 50, and the risk of developing it increases with age. Prostate can- what the form of treatment, the physician continues to measure PSA cer forms hard, solid nodules, most often in the posterior part of the levels in the patient’s blood to make sure all the cancerous structures prostate gland. Early stages of the cancer are generally asymptomatic, have been removed and to check for recurrence.

28.3g Penis Ejaculation (ē -jak-ū -lā sh ́ ŭn; eiaculatus = to shoot out) is the The penis (pē nis; ́ tail) and the scrotum form the external genitalia process by which semen is expelled from the penis with the help in males (figure 28.17a). Internally, the attached portion of the of rhythmic contractions of the smooth muscle in the wall of the penis is the root, which is dilated internal to the body surface, form- urethra. Sympathetic innervation (from the lumbar splanchnic ing both the bulb and the crura of the penis. The bulb attaches the nerves) is responsible for ejaculation. penis to the bulbospongiosus muscle in the urogenital triangle, and Although in most body systems sympathetic and parasympa- the crura attach the penis to the pubic arch. The body, or shaft, of thetic innervation tend to perform opposite functions, the male repro- the penis is the elongated, movable portion. The tip of the penis is ductive system is an exception. Here, parasympathetic innervation called the glans, and it contains the external urethral orifice. The is necessary to achieve an , while sympathetic innervation skin of the penis is thin and elastic. At the distal end of the penis, promotes ejaculation. Relaxation of autonomic activity after sexual the skin is attached to the raised edge of the glans and forms a cir- excitement reduces blood flow to the erectile bodies and shunts most cular fold called the prepuce (foreskin) (see Clinical View, p. 870 ). of the blood to other veins, thereby returning the penis to its flaccid Within the shaft of the penis are three cylindrical erectile condition. bodies (figure 28.17b). The paired corpora cavernosa (kav er-n ́ ō - să; sing., corpus cavernosum; caverna = grotto) are located dorso- laterally. Ventral to them along the midline is the single corpus spongiosum (spŭn ́jē -ō -sŭm), which contains the spongy urethra. Each corpus cavernosum terminates in the shaft of the penis, while Study Tip! the corpus spongiosum continues within the glans. The erectile One way to remember the autonomic innervation for the penis is bodies are ensheathed by the tunica albuginea, which also pro- this phrase: “Point and Shoot!” The p in point (erection) also stands for vides an attachment to the skin over the shaft of the penis. parasympathetic innervation, while the s in shoot (ejaculation) stands The erectile bodies are composed of a complex network of for sympathetic innervation. venous spaces surrounding a central artery. During sexual excite- ment, blood enters the erectile bodies via the central artery and fills in the venous spaces. As these venous spaces become engorged with blood, the erectile bodies become rigid, a process called WHATW DID YOU LEARN? erection (ē -rek sh ́ ŭn; erecto = to set up). The rigid erectile bodies compress the veins that drain blood away from the venous spaces. ●13 What two structures unite to form the ejaculatory duct? Thus, the spaces fill with blood, but the blood cannot leave the ●14 What is the composition of semen, and what organs contribute to erectile bodies until the sexual excitement ceases. Parasympathetic semen? innervation (via the pelvic splanchnic nerves) is responsible for ●15 Specifically, how do both parasympathetic and sympathetic increased blood flow and thus the erection of the penis. innervation work on penile function during ?

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CLINICAL VIEW

Circumcision

Circumcision (ser-ku˘m-sizh u ́˘n; circum = around, caedo = to cut) Pubic is the surgical removal of the prepuce (foreskin) of the penis. Membranous symphysis urethra The drawings here compare a circumcised penis (a) with an uncircumcised penis (b). Most are performed during Bulb of penis the first few days or weeks of a male ’s life, although some adult males do undergo the procedure. Circumcision is much more common in the United States than in other countries, and is the Right crus of penis subject of considerable debate. Corpora cavernosa Circumcision has several benefits: Circumcised males appear less Corpus spongiosum likely to develop urinary tract infections because the bacteria that cause these infections tend to stick to the foreskin. (However, if a child is taught early about keeping the penis clean, these Glans risks drop dramatically.) Circumcision may also protect against Scrotum penile inflammation (because the glans of a circumcised penis can be kept clean more easily) and penile cancer. Finally, some research has suggested that circumcised males have a reduced External urethral orifice risk of acquiring and passing on sexually transmitted diseases (a) Anterolateral view (STDs), including HIV. In 2006, the National Institutes of Health (NIH) announced that large, controlled clinical trials in Africa had demonstrated circumcision to be ef fective in preventing infection with and transmission of HIV. Circumcised men were approximately 50% less likely to become infected than uncircumcised men. Dorsal vein (blue), Deep dorsal artery (red), and The drawbacks to circumcision include the following: Infants are vein nerve (yellow) sometimes circumcised without anesthesia, subjecting them to Tunica albuginea pain and elevated stress levels. Circumcision also carries a risk Corpus Central artery of complications, including infection, excessive bleeding, and cavernosum Venous spaces in rare cases, subsequent surger y. Finally, some individuals have suggested that circumcision may affect sensation during sexual Deep fascia intercourse, although this hypothesis has not been systemati- Corpus spongiosum Superficial fascia cally tested or proven.

Skin Spongy urethra (b) Cross section Figure 28.17 Anatomy of the Penis. (a) An anterolateral view of the circumcised penis. (b) A diagrammatic, transverse section shows the arrangement of the erectile bodies.

Prepuce

(a) Circumcised penis (b) Uncircumcised penis

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CLINICAL VIEW Sexually Transmitted Diseases Genital herpes (her pe ́ ¯ z; herpo = to creep) is caused by herpes simplex virus type 1 (HSV-1) or type 2 (HSV-2). Infected individu- Sexually transmitted diseases (STDs), also known as venereal diseases, als undergo cyclic outbreaks of blister formation in the genital and are a group of infectious diseases that are usually transmitted via sexual anal regions; the blisters are filled with fluid containing millions of contact. The incidence of STDs has been rising in recent years because infectious viruses. The blisters then break and turn into tender sores individuals are having sexual intercourse at younger ages, and may have that remain for 2–4 weeks. Typically, future cycles of blistering are multiple sexual partners in their lifetime. Many times, the symptoms of less severe and shorter in duration than the initial episode. There is STDs are not immediately noticeable, so infected individuals may spread no cure for herpes, but antiviral medications can lessen the severity the disease to someone else without realizing it. Mothers also may trans- and length of an outbreak. mit STDs to their newborns, either directly across the placenta or at the Gonorrhea (gon-o¯-re¯ a ˘)́ is caused by the bacterium Neisseria gonor- time of delivery. Condoms, when properly used, have been shown to help rhoeae, and is spread either by sexual contact or from mother to new- prevent the spread of STDs, but they are not 100% effective. Individuals born at the time of delivery. Symptoms include painful urination and/or with multiple sex partners should consider being tested routinely for some a yellowish discharge from the penis or vagina. Gonorrhea is treated of the more common STDs, because they may unknowingly be spreading with antibiotics, although in recent years many gonorrhea strains have one or more of these conditions. become resistant to some antibiotics. If untreated, women may develop STDs are a leading cause of pelvic inflammatory disease in women, pelvic inflammatory disease, and men may develop epididymitis, a in which the pelvic organs (uterus, uterine tubes, and ovaries) become painful condition of the epididymis that can lead to infertility. If a infected. Should bacteria from an STD infect the uterus and uterine newborn acquires the disease, then blindness, problems, and/or tubes, scarring is likely to follow, leading to blockage of the tubes and a life-threatening blood infection may result. infertility. We’ve already discussed two types of STDs, human papil- Syphilis (sif ́i-lis) is caused by the corkscrew-shaped bacterium lomavirus (see Clinical View, “Cervical Cancer,” earlier in this chapter) Treponema pallidum. The bacterium is spread sexually via contact and AIDS (in chapter 24). We now explore other common STDs. with a syphilitic sore (called a chancre), or a newborn may acquire Chlamydia (kla-mid e ¯́ -a˘) is the most frequently reported bacterial STD in it in utero. Babies can acquire congenital syphilis from their mothers the United States. The responsible agent is Chlamydia trachomatis. Most and are often stillborn, but if they live, they have a high incidence of infected people are asymptomatic, while the rest develop symptoms skeletal malformities and neurologic problems. Syphilis can be treated within 1 to 3 weeks after exposure. These symptoms include abnormal with antibiotics. A person can become reinfected with the disease if vaginal discharge, painful urination (in both males and females), and reexposed to the syphilitic sores. low back pain. Chlamydia is treated with antibiotics.

lubricated lining. The uterus shrinks and atrophies, becoming 28.4 Aging and the Reproductive much smaller than it was before puberty. The lack of significant amounts of estrogen and progester- Systems one in a menopausal woman also affects other organs and body Learning Objective: systems. Women may experience “hot flashes,” in which their bodies perceive periodic elevations in body temperature, and they 1. Outline the age-related changes that occur in the female may develop thinning scalp hair and/or an increase in . and male reproductive systems. Menopausal women are at greater risk for osteoporosis (thinning, Our reproductive systems are basically nonfunctional for brittle ) and disease due to the drop in estrogen and several years following birth. When we reach puberty, hormonal progesterone levels. Menopausal hormone therapy (MHT), in the changes in the hypothalamus and anterior pituitary stimulate the form of estrogen and progesterone supplements primarily, can be gonads to begin producing sex hormones. Thereafter, changes occur prescribed to peri- and postmenopausal women to help diminish in many body structures, the reproductive organs mature, and the these symptoms and risks. However, the risks associated with MHT gonads begin to produce gametes. The time of onset of puberty var- (e.g., increased risk of breast cancer, stroke, heart attack, and blood ies among individuals, but it clearly occurs at a younger average age clots) may outweigh the benefits, so physicians assess each indi- in females and males today than it did 40 or 50 years ago. vidual for her suitability for MHT. Studies regarding MHT continue. After reaching sexual maturity, the female and male repro- In contrast, males do not experience the relatively abrupt ductive systems exhibit marked differences in their response to change in reproductive system function that females do. A slight aging. Gametes typically stop maturing in females by their 40s decrease in the size of the testes parallels a reduction in the size of or 50s, and menopause occurs. A reduction in hormone produc- the seminiferous tubules and the number of interstitial cells. As a tion that accompanies menopause causes some atrophy of the consequence of the reduced number of interstitial cells, decreased reproductive organs and the breasts. The vaginal wall thickness testosterone levels in males in their 50s signal a change called the decreases, as do glandular secretions for maintaining a moist, male climacteric (klı̄-mak ter-ik, ́ klı̄-mak-ter ́ik). However, males

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generally do not stop producing gametes as females do following In contrast, phenotypic (fē n ́ ō -tip ́ik, fen ́ō -) sex refers to the menopause. appearance of an individual’s internal and external genitalia. A Most males experience prostate enlargement (either benign person with ovaries and female external genitalia (labia) is a pheno- or cancerous) as they age. This prostate enlargement can interfere typic female, whereas a person with testes and male external geni- with sexual and urinary functions. Also associated with aging are talia (penis, scrotum) is a phenotypic male. Phenotypic sex starts to erectile dysfunction and impotence, which refer to the inability become apparent no earlier than the seventh week of development. to achieve or maintain an erection. Besides aging, other risk fac- How does the primordial tissue know whether to develop into tors for this condition include heart disease, diabetes, smoking, female reproductive organs or male reproductive organs? In males, and prior prostate surgery. Many drugs have entered the market the sex-determining region Y (SRY) is located within the larger (e.g., sildenafil [Viagra]) that treat erectile dysfunction by prolong- testis-determining factor (TDF) region on the . If the ing vasodilation of the penile arteries and thus inhibiting relax- Y chromosome is present, the SRY gene produces proteins to stimulate ation of the erectile bodies. the production of other hormones (e.g., testosterone and other andro- gens) that initiate male phenotypic development. If a Y chromosome WHATW DID YOU LEARN? is absent (e.g., the individual is a genetic female), or if the Y chromo- some is either lacking or has an abnormal SRY gene, a female pheno- ●16 What are some female body changes that accompany menopause? typic sex results. Although undoubtedly more complicated, the female phenotypic sex may be thought of as the organism’s default pattern. 28.5 Development of the This pattern is not changed unless SRY and its proteins are present. Reproductive Systems 28.5b Formation of Indifferent Gonads Learning Objectives: and Genital Ducts 1. Describe the development of the female and male Early in the fifth week of , paired genital reproductive systems. ridges (or gonadal ridges) form from intermediate . The 2. Detail the common embryonic structures and the genital ridges will form the gonads. These longitudinal ridges are hormones that influence their development. medial to the developing kidneys at about the level of the tenth thoracic vertebra (figure 28.18, top). Between weeks 5 and 6, pri- The female and male reproductive structures originate from mordial germ cells migrate from the sac to the genital ridges. the same basic primordia, which differentiate into female or male These germ cells will form the future gametes (either sperm or structures, depending upon the signals the primordia receive. To oocytes). Shortly thereafter, two sets of duct systems are formed: better explain this process, we must first distinguish between the genetic and phenotypic sex of an individual. ■ The mesonephric (mez-ō -nef rik) ́ ducts (or Wolffian ducts) form most of the male duct system. Recall that 28.5a Genetic Versus Phenotypic Sex the mesonephric ducts also connect the Genetic sex (or genotypic sex) refers to the sex of an individual (intermediate ) to the developing urinary bladder. based on her or his sex chromosomes. An individual with two ■ The paramesonephric ducts (Müllerian ducts) form most of X chromosomes is a genetic female, while an individual with one the female duct system, including the uterine tubes, uterus, X and one Y chromosome is a genetic male. Genetic sex is deter- and superior part of the vagina. These ducts appear lateral mined at fertilization. to the mesonephric ducts.

CLINICAL VIEW True Hermaphroditism and majora. Male pseudohermaphroditism usually results from a reduction Pseudohermaphroditism in male hormones (e.g., testosterone) during development; thus, the sex-determining region Y (SRY) gene on the Y chromosome is present, The term (her-maf ro ́ ¯-dı¯t) is derived from the Greek but its proteins are insufficient in the absence of testosterone to name Hermaphroditus, the mythological son of the Greek god Hermes masculinize the external genitalia. and the goddess Aphrodite. In general, a hermaphrodite is an individual A female pseudohermaphrodite is a genetic female (XX) with exter- with both male and female sex characteristics. True hermaphroditism nal genitalia that resemble those of a male (male phenotypic sex). refers to an individual with both ovarian and testicular structures and Although the ovaries and internal genitalia (e.g., uterine tubes and ambiguous (or female) external genitalia. The person may be a genetic uterus) are female, the external genitalia (clitoris and labia) resemble male (XY) or a genetic female (XX). True hermaphroditism is very rare, male external sex organs. The clitoris enlarges to look like a small and typically the ovarian and testicular structures are not functional. penis, and/or the two labia may become partially fused to resemble Pseudohermaphroditism (soo ́do¯-her-maf ro ́ ¯-dı¯-tizm; pseudes = false) a scrotum. Female pseudohermaphroditism may result if the female refers to an individual whose genetic sex and phenotypic sex do not fetus is exposed to excessive androgens (e.g., if the pregnant mother match. A male pseudohermaphrodite is a genetic male (XY) whose was given certain medications to help prevent miscarriage). More external genitalia resemble those of a female (female phenotypic sex). commonly, female pseudohermaphroditism is caused by congenital These individuals usually have testes, but the structures that form the adrenal hyperplasia, in which the fetus’s adrenal glands produce scrotum do not fuse completely, so the structure looks more like labia excessive amounts of androgens.

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Sexually Indifferent Stage

Mesonephros

Genital ridge

Kidney

Cloaca

Weeks 5–6

Female Male

Testes Ovaries Efferent ductules Paramesonephric duct forming the Epididymis uterine tube Paramesonephric Mesonephric duct (degenerating) duct (degenerating) Mesonephric duct forming the ductus Fused paramesonephric Urinary bladder ducts forming the uterus deferens Urinary bladder (moved aside) Seminal vesicle

Urogenital sinus forming forming the urethra the urethra and inferior vagina

Weeks 10–12 Weeks 10–12

Uterine tube Urinary bladder

Ovary Seminal vesicle Uterus Prostate gland

Ductus deferens Urethra Urinary bladder Epididymis (moved aside) Vagina Efferent ductules Testis

Urethra Hymen

At birth At birth Figure 28.18 Embryonic Development of the Female and Male Reproductive Tracts. Through the first 6 weeks of development, the embryo is termed “sexually indifferent.” Thereafter, genetic expression determines sex differentiation.

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All human develop both duct systems, but only one It is common for premature male babies to have undescended tes- of the duct systems remains in the fetus. If the embryo is female, tes because they were born before the testes had fully descended the paramesonephric ducts develop, and the mesonephric ducts into the scrotum. Their testes usually descend shortly after birth. degenerate. If the embryo is male, the mesonephric ducts grow and differentiate into male reproductive structures, while the parame- 28.5d External Genitalia Development sonephric ducts degenerate. As with the internal genitalia, female and male external genitalia develop from the same primordial structures (figure 28.19). By 28.5c Internal Genitalia Development the sixth week, the following external structures are seen: The development of the female internal reproductive structures is ■ The urogenital folds (or urethral folds) are paired, elevated traced in figure 28.18, left. Because no SRY proteins are produced structures on either side of the urogenital membrane, a thin in the female, the mesonephric ducts degenerate. Between weeks 8 partition separating the urogenital sinus from the outside of and 20, the paramesonephric ducts develop and differentiate. The the body (see chapter 27). caudal (inferior) ends of the paramesonephric ducts fuse, form- ■ The is a rounded structure anterior to the ing the uterus and the superior part of the vagina. The cranial urogenital folds. (superior) parts of the paramesonephric ducts remain separate and ■ The labioscrotal swellings (or genital swellings) are paired form two uterine tubes. The remaining inferior part of the vagina elevated structures lateral to the urethral folds. is formed from the urogenital sinus (which also forms the urinary bladder and urethra). The external genitalia appear very similar between females By about week 7 of development, the SRY gene on the Y chro- and males until about week 12 of development, and they do not mosome begins influencing the indifferent to become a tes- become clearly differentiated until about week 20. In the absence tis, which then forms sustentacular cells and interstitial cells. Once of testosterone, female external genitalia develop. The genital the sustentacular cells form, they begin secreting anti-Müllerian tubercle becomes the clitoris. The urogenital folds do not fuse, but hormone (AMH) (also known as Müllerian inhibiting substance), become the labia minora. Finally, the labioscrotal folds also remain which inhibits the development of the paramesonephric ducts (see unfused and become the labia majora. In the male, production and figure 28.18, right). These paramesonephric ducts degenerate, and circulation of testosterone cause the primitive external structures between weeks 8 and 12, the mesonephric ducts form the male to differentiate. The genital tubercle enlarges and elongates, form- duct system—efferent ductules, epididymides , ductus deferens, ing the glans of the penis and part of the dorsal side of the penis. seminal vesicles, and ejaculatory ducts. The urogenital folds grow and fuse around the developing urethra The prostate and bulbourethral glands do not form from the and form the ventral side of the penis. Finally, the labioscrotal mesonephric ducts. Instead, they begin to form as endodermal swellings fuse at the midline, forming the scrotum. “buds” or outgrowths of the developing urethra between weeks 10 and 13. As the prostate gland and bulbourethral glands develop, they incorporate mesoderm into their structures as well. Finally, note that the indifferent gonad originates near Study Tip!

the level of thoracic vertebra T10. Throughout prenatal develop- You may be aware that the sex of an unborn child can typically be ment, the developing testis descends from the abdominal region determined with an ultrasound sometime between weeks 18 and 22. toward the developing scrotum. A thin band of connective tissue You now know why the physician waits until this time—it is when the called the (goo ́ber-nek ́ū -lŭm; helm) attaches to external genitalia first become clearly distinguishable. the testis and pulls it from the abdomen, through the developing inguinal canal, to its placement in the scrotum. As the embryo grows (but the gubernaculum remains the same length), the testis WHATW DID YOU LEARN? is passively pulled into the scrotum. This process is slow, begin- ning in the third month and not completed until the ninth month. ●17 What is the difference between genetic and phenotypic sex?

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(a) Sexually indifferent stage

Genital tubercle

Urogenital fold Figure 28.19 Development of External Genitalia. (a) At 6 weeks of development, the external genitalia are undifferentiated. Labioscrotal (b) By 12 weeks, the urogenital folds begin to fuse in the swelling male and remain open in the female. (c) By 20 weeks, external genitalia are well differentiated.

Week 6

Female Male

Developing clitoris Developing glans of penis

Labia minora

Labia majora

Anus

(b) Week 12: Urogenital folds begin to fuse in the male

Urethral orifice Glans of penis

Glans of clitoris

Urethral orifice Vaginal orifice

Scrotum

Anus

(c) Week 20: External genitalia well differentiated

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Clinical Terms

(kas-trā sh́ ŭn; castro = to deprive of generative dysmenorrhea (dis-men-ō r-rē ́ă ; dys = bad, men = month, rhoia = power) Removal of the testes or ovaries. flow) Difficult and painful menstruation. cryptorchidism (krip-tō r ki-dizm;́ krypto = hidden, orchis = testis) A salpingitis Inflammation of the uterine tubes. testis that has not descended completely into the scrotum.

Chapter Summary

28.1 Comparison ■ Both reproductive systems have gonads that produce gametes and sex hormones, and a duct system to transport the gametes. of the Female and Male Reproductive 28.1a Perineum 843 Systems 843 ■ In both females and males, the perineum is a diamond-shaped area between the thighs that contains the urogenital and anal triangles.

28.2 Anatomy ■ Female internal reproductive organs include paired ovaries and uterine tubes, a uterus, and a vagina. of the Female Reproductive 28.2a Ovaries 845 System 844 ■ The cortex of the ovary houses ovarian follicles that consist of an oocyte surrounded by follicle cells. ■ Changing levels of FSH and LH cause a primordial follicle to mature into a primary follicle. A secondary follicle matures from a primary follicle, and a vesicular follicle matures from a secondary follicle. ■ A peak in LH causes the secondary oocyte to be released from the vesicular follicle at ovulation; remaining follicular cells become the hormone-producing corpus luteum. ■ The ovarian cycle consists of the follicular phase, ovulation, and the luteal phase. 28.2b Uterine Tubes 852 ■ The uterine tubes are the site of fertilization. They have an infundibulum, ampulla, isthmus, and uterine part. ■ The uterine tube wall is composed of an inner mucosa (ciliated columnar epithelium), middle muscularis (two smooth muscle layers), and an external serosa. 28.2c Uterus 852 ■ The uterus is a thick-walled muscular organ that functions as the site of pre-embryo implantation, supports and nourishes the embryo/fetus, ejects the fetus at birth, and is the site of menstruation. ■ The uterine wall consists of an inner mucosa, the endometrium; a thick-walled middle , the myometrium; and an outer serosa, the perimetrium. ■ The endometrium has a functional layer that is sloughed off as menses and a deeper basal layer that regenerates a new functional layer during the next uterine cycle. ■ Three distinct phases of endometrium development occur during the uterine cycle: menstrual phase, proliferative phase, and secretory phase. 28.2d Vagina 855 ■ The vagina is a fibromuscular tube that serves as the birth canal for the fetus, a receptacle for the penis during intercourse, and the passageway for menstrual discharge. 28.2e External Genitalia 857 ■ The external female sex organs, collectively called the vulva, include the mons pubis, labia majora, labia minora, and the clitoris. 28.2f Mammary Glands 857 ■ The paired mammary glands produce breast milk. ■ Prolactin is responsible for milk production; oxytocin is responsible for milk ejection.

28.3 Anatomy ■ The primary male reproductive system organs are the testes; accessory sex organs include ducts, male accessory glands, of the Male and the penis. Reproductive System 861 28.3a Scrotum 861 ■ The scrotum houses the testes outside the male body, where the lower temperature is needed to form functional sperm. 28.3b Spermatic Cord 863 ■ The spermatic cord transmits blood vessels and nerves from the to the testis. 28.3c Testes 863 ■ The testis contains up to four seminiferous tubules. Between the seminiferous tubules are interstitial cells, which produce androgens. ■ Seminiferous tubules contain sustentacular cells and developing sperm cells. ■ Sustentacular cells nourish developing sperm cells. ■ Spermatogenesis is the meiotic process that forms haploid spermatids. ■ Spermiogenesis is the process by which spermatids differentiate into sperm.

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28.3 Anatomy 28.3d Ducts in the Male Reproductive System 866 of the Male ■ Ducts store and transport sperm. They include the rete testis, the efferent ductules, the epididymis, the ductus deferens, Reproductive and the ejaculatory duct. System ■ (continued) 861 The male urethra carries urine or semen at any one time. 28.3e Accessory Glands 867 ■ Accessory glands produce seminal fluid, a nutrient-rich, alkaline fluid that supports sperm. Accessory glands include seminal vesicles, the prostate gland, and the bulbourethral glands. 28.3f Semen 868 ■ Semen is a mixture of seminal fluid and sperm. 28.3g Penis 869 ■ The penis is the copulatory organ. ■ The body of the penis contains three parallel erectile bodies and the urethra.

28.4 Aging and ■ Females undergo a change in reproductive structure and called menopause. Males undergo a male climacteric in the Reproductive which the production of testosterone is measurably reduced. Systems 871

28.5 Development ■ Both male and female reproductive structures originate from the same basic primordia. Gene expression determines how of the they differentiate. Reproductive Systems 872 28.5a Genetic Versus Phenotypic Sex 872 ■ Genetic sex is based on chromosome type; phenotypic sex refers to the appearance of the internal and external genitalia. 28.5b Formation of Indifferent Gonads and Genital Ducts 872 ■ Early in development, genital ridges form from . Primordial germ cells migrate from the to the genital ridges and form the future gametes. 28.5c Internal Genitalia Development 874 ■ In the absence of sex-determining region Y (SRY) gene, the female reproductive pattern develops. The male reproductive pattern develops as a result of the SRY gene and its proteins. 28.5d External Genitalia Development 874 ■ The external genitalia appear very similar until about week 12; external genitalia become fully differentiated about week 20.

Challenge Yourself

Matching Multiple Choice Match each numbered item with the most closely related lettered Select the best answer from the four choices provided. item. ______1. In the male, what cells produce androgens? ______1. vagina a. houses the testes a. spermatogonia b. interstitial cells ______2. uterus b. produces follicles and sex c. sustentacular cells hormones ______3. clitoris d. All of these are correct. c. secretion is milky; contains ______4. testes ______2. All of the following organs produce a component of citric acid seminal fluid except the ______5. ovary d. contains three erectile bodies a. bulbourethral glands. ______6. prostate gland b. testes. e. normal site for implantation of a c. seminal vesicles. ______7. scrotum pre-embryo d. prostate gland. ______8. uterine tube f. fertilization normally occurs ______3. Spermatogonia divide by mitosis to form a new here spermatogonium and ______9. penis a. a sperm. g. composed of both sperm and ______10. semen b. spermatids. seminal fluid c. a primary spermatocyte. h. birth canal d. . i. produces spermatozoa ______4. Sperm are stored in the ______, where they remain until they are fully mature and capable of motility. j. contains two erectile bodies a. epididymis c. ductus deferens b. seminiferous tubule d. rete testis

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______5. The female homologue to the penis is the Content Review a. labia majora. 1. What are some similarities between the male and female b. labia minora. reproductive systems? What are the anatomic homologues c. clitoris. between these systems? d. vagina. 2. What hormones are associated with the female reproductive ______6. Ovulation occurs due to a dramatic “peak” in which system, and what is the function of each hormone? hormone? a. progesterone 3. Identify the regions of the uterine tube. b. LH 4. List the uterine wall layers, and describe the basic anatomy c. FSH of each layer. d. prolactin 5. Compare and contrast the ovarian cycle phases and the ______7. Which statement is true about the uterus? uterine cycle phases. When do they occur? What specific a. The basal layer of the endometrium is shed each events are associated with each phase? month during menses. 6. Describe these parts of the mammary gland: nipple, areola, b. The myometrium is composed of several layers of lobe, lobule, and alveoli. skeletal muscle. 7. What is the function of sustentacular cells in the production c. The cervix projects into the vagina. of spermatozoa? d. The round ligament is peritoneum that drapes over the uterus. 8. Describe the process of spermatogenesis, including which cells are diploid and which are haploid. ______8. Which structure contains a primary oocyte, several layers of granulosa cells, and an antrum? 9. Compare the secretions of the seminal vesicles, the prostate a. primordial follicle gland, and the bulbourethral glands. b. primary follicle 10. What changes occur in the penis to allow a male to attain c. secondary follicle an erection? d. vesicular follicle Developing Critical Reasoning ______9. The most anteriorly placed structure in the female perineum is the 1. Caitlyn had unprotected sex with her fiancé approximately a. vaginal orifice. 2 weeks after her last period, and is worried that she might b. cervix. have become pregnant. She asks her physician if there are c. labia minora. times during her monthly menstrual cycle when she might d. mons pubis. be more likely to become pregnant. She also asks how birth ______10. The paramesonephric ducts in the embryo form control pills prevent a woman from becoming pregnant. which of the following? What will the physician tell Caitlyn? a. uterine tubes and uterus 2. If parents wish to know the sex of their unborn baby, they b. ovary usually have to wait until weeks 18–22 of development c. ductus deferens before a sonogram determining the sex can be performed. d. seminal vesicle Based on your knowledge of reproductive system development, explain why the sex of the unborn baby can’t be determined easily before this time.

Answers to “What Do You Think?”

1. A woman can become pregnant as long as she has one the small amount produced by the adrenal glands would remaining functioning ovary. have little effect on the male. 2. Stress, age, medications, and body weight all can affect 4. If a male has a vasectomy, sperm still form in the a woman’s monthly uterine (menstrual) cycle. Stress seminiferous tubule and then mature in the epididymis. and excessively lean body mass can lead to amenorrhea However, since the sperm are not ejaculated, they die, (absence of periods). and their components are broken down and resorbed in 3. If a male’s testes were removed, the adrenal glands could the epididymis. An individual who has had a vasectomy still produce a small amount of androgens. However, since ejaculates seminal fluid only, not semen (which contains the testes produce the overwhelming majority of androgens, sperm).

www.mhhe.com/mckinley3 Enhance your study with practice tests and activities to assess your understanding. Your instructor may also recommend the interactive eBook, individualized learning tools, and more.

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