Human Reproduction and Development Section 1 Reproductive Systems -!). )DEA Hormones regulate human reproductive systems, including the production of gametes. Section 2 Human Development Before Birth -!). )DEA A human develops from a single fertilized cell into trillions of cells with specialized functions. Section 3 Birth, Growth, and Aging Fetal hand—20 weeks -!). )DEA Developmental changes continue throughout the stages of life. BioFacts Fetal hand—6 weeks • A human embryo increases in size 10,000 times in the first 30 days. • The largest human newborn weighed 10.8 kg at birth. • In 2002, 96.7 percent of all live ▶ births in the United States were ▶ single births and 3.3 percent were multiple births. ▶ ▶ Fetal hand—5 weeks 1046 ((t)Lennartt)Lennart Nilsson/Bonnier-AlbaNilsson/Bonnier-Alba , (b)Biophoto(b)Biophoto AAssociates/Photossociates/Photo RResearchersesearchers , (bkgd)Neil(bkgd)Neil Bromhall/GenesisBromhall/Genesis Films/SPL/PhotoFilms/SPL/Photo ResearchersResearchers 11046-1047_C36-CO_869510.indd046-1047_C36-CO_869510.indd 11046046 55/9/06/9/06 33:29:52:29:52 PPMM SStart-Uptart-Up AActivitiesctivities Reproductive System Make LAUNNCHCH LLabab this Foldable to help you compare and contrast the Sex Cell Characteristics production of eggs and sperm. How are sex cells specialized for the formation of a STEP 1 Draw a horizontal line along zygote? Reproduction is a process which follows a the middle of a sheet of notebook paper predictable pattern. The production of sex cells is a as shown. crucial step in reproduction. Sperm and egg cells have specific characteristics that support their roles in reproduction. In this lab, you will investigate how the design of sex cells supports their function. Procedure 1. Read and complete the lab safety form. 2. Observe the slide of the egg cell under the microscope and identify its characteristics. Make a sketch. STEP 2 Fold the paper from the top and bottom so the edges meet at the 3. Observe the slide of the sperm cell under center line. the microscope and identify its characteris- tics. Make a sketch. Analysis 1. Compare and contrast the sperm and egg cells you studied. How do they differ? 2. Identify What structures and characteristics STEP 3 Label the two tabs as shown. did you observe that might affect each cell’s role in reproduction? -«iÀÊ*À`ÕVÌ }}Ê*À`ÕVÌ &/,$!",%3 Use this Foldable with Section 36.1. As you study the section, use the Foldable to record what you learn about the production of sperm in the testes and the Visit biologygmh.com to: production of eggs in the ovary. ▶ study the entire chapter online ▶ explore Concepts in Motion, Interactive Tables, Microscopy Links, and links to virtual dissections ▶ access Web links for more information, projects, and activities ▶ review content online with the Inter- active Tutor, and take Self-Check Quizzes Chapter 36 •Sectio Humann Reproduction1 • XXXXXXXXXXXXXXXXXX and Development 1047 11046-1047_C36-CO_869510.indd046-1047_C36-CO_869510.indd 11047047 55/9/06/9/06 33:30:27:30:27 PPMM Section 36.1 Objectives Reproductive Systems ◗ Summarize the structures of the male and female reproductive systems and discuss the functions of each. -!). )DEA Hormones regulate human reproductive systems, ◗ Explain how hormones regulate the including the production of gametes. male and female reproductive systems. Real-World Reading Link You might have noticed how the temperature of ◗ Discuss the events that take place a room affects the thermostat that controls furnace activity. If the room is warm, during a menstrual cycle. the thermostat will not allow the furnace to run. Similarly, male and female hormones in the human body have effects on body structures and influence Review Vocabulary human reproduction. hypothalamus: portion of the brain that connects the endocrine and nervous systems, and controls the Human Male Reproductive System pituitary gland Reproduction is necessary to ensure continuation of a species. The New Vocabulary result of the human reproductive process is the union of an egg cell and a sperm cell, development of the fetus, and the birth of an infant. The seminiferous tubule epididymis organs, glands, and hormones of the male and female reproductive sys- vas deferens tems are instrumental in meeting this goal. urethra Figure 36.1 illustrates the male reproductive structures. The male semen reproductive glands are called the testes (tes TEEZ) (singular, testis) puberty and are located outside of the body cavity in a pouch called the scro- oocyte tum (SKROH tum). A temperature lower than 37°C—the average oviduct body temperature—is required for the development of sperm. menstrual cycle Because the scrotum is located outside of the body cavity, it is several polar body degrees cooler. This makes the environment suitable for the normal development of sperm. ■ Figure 36.1 The male reproductive system produces gametes called sperm in the testes. Male Reproductive System Side view Posterior view Bladder Bladder Sacrum Vas deferens Seminal vesicle Pubic bone Prostate gland Vas deferens Bulbourethral gland Urethra Urethra Cross section Rectum Penis of epididymis Cross section of testis Epididymis Seminiferous tubule Testis Epididymis Testis Scrotum Penis 1048 Chapter 36 • Human Reproduction and Development 11048-1053_C36–S1_869510.indd048-1053_C36–S1_869510.indd 11048048 44/26/06/26/06 110:48:430:48:43 AAMM Sperm cells The male reproductive cells, called sperm Tail (55 µm) cells, are produced in the testes. Follow the path that sperm travel in Figure 36.1 as you read about the structures in the Middle male reproductive system. Sperm, like the one shown in piece (6 µm) Fibrous Figure 36.2, develop in the testes in the seminiferous Head sheath of tubules (se muh NIHF rus • TEW byulz). These tubules pro- (5 µm) flagellum duce 100–200 million sperm each day. Next, sperm travel to the epididymis (eh puh DIH duh mus), a structure located on º top of each testis where sperm mature and are stored. When the sperm are released from the body, they travel through the vas deferens (VAS • DEF uh runz), a duct leading away from Acrosome Nucleus the testis. There are two vas deferens, one leading away from ■ Figure 36.2 A sperm is a flagellated cell composed of each testis. The two vas deferens join together and enter the a head, midpiece, and tail. urethra (yoo REE thruh), the tube that carries both semen List, in correct sequence, the structures a sperm cell and urine outside of the body through the penis. passes through or encounters as it makes its way Sperm require a nourishing fluid to survive long out of the body. enough to fertilize an egg. Semen (SEE mun) refers to the fluid that contains sperm, the nourishment, and other fluids from the male reproductive glands. The seminal vesicles contribute over half of the semen and secrete sugar into the fluid, which provides energy, other nutrients, pro- teins, and enzymes for the sperm. The prostate gland and bulbourethral glands contribute an alkaline solution to the fluid to neutralize acidic conditions sperm might encoun- ter in the urethra and the female reproductive tract. ■ Figure 36.3 The hypothalamus produces the releasing Male hormones hormone GnRH that travels to the pituitary gland. GnRH Testosterone (tes TAHS tuh rohn), which influences the rate of LH and FSH production. The levels of is made in the testes, is a steroid hormone that is necessary for LH and FSH are regulated by a negative feedback pathway. the production of sperm. It also influences the development of male secondary sex characteristics that begin to appear at puberty, the period of growth when sexual maturity is Hypothalamus reached. These characteristics include hair on the face and produces GnRH chest, broad shoulders, increased muscle development, and a deeper voice. Recall from Chapter 34 that the larynx con- tains the vocal cords. Because the vocal cords are longer in males than in females, the male voice is deeper. Later in life, testosterone might lead to a receding hairline or baldness. Three hormones influence testosterone production. Figure 36.3 indicates that the hypothalamus, discussed in Chapter 33, produces gonadotropin-releasing hormone Capillary (GnRH) that acts on the anterior pituitary gland. GnRH increases the production of follicle-stimulating hormone (FSH) and luteinizing (LEW tee uh ni zing) hormone (LH). Both FSH and LH travel from the anterior pituitary gland Anterior through the bloodstream and to the testes. In the testes, FSH pituitary promotes the production of sperm, and LH stimulates the pro- duction and secretion of testosterone. Levels of the male hormones are regulated by a negative feed- Capillary back system that starts with the hypothalamus. Increased levels of testosterone in the blood are detected by cells in the hypothal- amus and anterior pituitary, and the production of LH and FSH is decreased. When testosterone levels in the blood drop, the FSH and LH released Posterior body responds by making more LH and FSH, as shown in to general circulation pituitary Figure 36.3. Section 1 • Reproductive Systems 1049 11048-1053_C36–S1_869510.indd048-1053_C36–S1_869510.indd 11049049 44/26/06/26/06 110:48:500:48:50 AAMM /VIDUCT 5TERUS /VIDUCT /VARY #ERVIX /VARY %GG #ORPUS "LADDER RELEASED LUTEUM &OLLICLE FORMS 0UBIC RUPTURES BONE &OLLICLE 6AGINA %GG 5RETHRA &OLLICLE DEVELOPS 2ECTUM %GGDEVELOPS !NUS ■ Figure 36.4 Left: The main structures of the female repro ductive system are the vagina, uterus, Human Female and ovaries. Right: During every menstrual cycle, one follicle Reproductive System fully matures and releases an egg. The follicle is A female’s reproductive system is specialized to produce egg cells, then called the corpus luteum. receive sperm, and provide an environment that is right for fertilization Predict What might be the result if of an egg and the development of an embryo. Refer to Figure 36.4 as more than one follicle fully develops you read about the structures of the female reproductive system.