X X Sperm Egg XX = Female XY = Male

Home , Perineal raphe, Tunica vaginalis

Table 27.1 Fig. 27.2

X X XX = female

Sperm Egg

Y X XY = male

1 2

Mesonephros Mesonephric duct Genital tubercle

Gonadal ridge Paramesonephric Urogenital fold (müllerian) duct Labioscrotal fold Kidney Tail

Cloaca 6 weeks

5- to 6-week embryo; sexually indifferent stage Male Female

Testes Ovaries Efferent ductules Paramesonephric 8 weeks Epididymis duct forming the uterine tube Paramesonephric Male Female duct (degenerating) Mesonephric duct Phallus: (degenerating) Developing glans Mesonephric duct Developing glans Fused paramesonephric of penis forming the of clitoris ductus deferens ducts forming the uterus Urinary bladder Urethral groove Labia minora Urinary bladder Seminal vesicle (moved aside) Urethral groove Urogenital sinus Urogenital sinus Labia majora forming the urethra forming the urethra and lower vagina Anus 7 to 8 weeks 8 to 9 weeks Anus 10 weeks 10 weeks

Urethral orifice Urinary Uterine bladder Glans of penis Prepuce tube Seminal Ovary Prepuce Glans of clitoris vesicle Uterus Prostate gland Urethral orifice Bulbourethal gland Vaginal orifice Scrotum Ductus deferens Urinary bladder (moved aside) Epididymis Vagina Perineal raphe Perineal raphe Urethra Testis Anus Urethra Hymen Anus

Penis Vestibule 12 weeks 12 weeks At birth At birth 3 4

Fig. 27.5 Fig. 27.6

Location of pubic symphysis

3-month fetus 8-month fetus 1-month-old infant

Parietal Closed proximal peritoneum Muscular wall of abdomen portion of Epididymis vaginal process Perineal raphe Testis Inguinal canal Ductus deferens Spermatic cord Pubic symphysis Vaginal process Vaginal process Tunica vaginalis Gubernaculum Scrotum Scrotal swelling Penis Gubernaculum

Urogenital triangle Location of Location of ischial coccyx tuberosity Anal triangle Anus

Pelvic cavity

External inguinal ring 37°C

Spermatic cord: Cremaster muscle Testicular artery Pampiniform plexus

Testicular artery Blood flow Blood flow Fascia of spermatic cord Ductus deferens Superficial fascia of penis Deep fascia of penis

Pampiniform plexus Prepuce (foreskin) Heat transfer

Epididymis Glans Arterial blood cools Venous blood carries Tunica vaginalis Median septum of scrotum as it descends away heat as it ascends Testis Cremaster muscle

Dartos muscle Key Scrotal skin 35°C Warmest Coolest blood blood Testis 7 8

Spermatic Spermatic cord cord

Blood vessels Ductus deferens and nerves Urinary bladder Rectum Head of Pubic Head of symphysis Ampulla of ductus deferens epididymis epididymis Ductus Root of Seminal vesicle penis deferens Ejaculatory duct Seminiferous Efferent Ductus (vas) deferens Prostate gland ductule tubule Septum Bulbourethral Rete testis Shaft of penis gland Testis, covered Bulbospongiosus Body of Lobule Corpus cavernosum by tunica muscle epididymis Corpus spongiosum albuginea Urethra Epididymis Tunica Glans of penis vaginalis Prepuce Tail of epididymis Testis Tunica Scrotum Scrotum (folded down) albuginea Ureter Tail of Urinary epididymis bladder (a) 2 cm (b) Ampulla

(a) Sagittal section Interstitial cells Seminal vesicle Blood vessel Germ cells Blood vessel Ejaculatory Prostate duct gland Sustentacular cell Seminiferous tubule Prostatic Bulbourethral urethra gland

Tails of Spermatids Bulb spermatozoa Membranous urethra Crus Sustentacular cell nuclei Ductus deferens Corpus spongiosum Tubule lumen Corpus Germ cells cavernosum (c) Connective tissue Efferent wall of tubule ductules Testis

Epididymis Interstitial cells

Spongy (penile) urethra

Glans of penis

(d) 50 µm Penis a: ©McGraw-Hill Education/Dennis Strete; c: ©Dr. Kessel & Dr. Kardon/Tissues and Organs/Visuals Unlimited, Inc.; d: ©Ed Reschke 9 (b) Posterior view 10

1 GnRH Secondary sex characteristics + Dorsal vein Dorsal 1 GnRH from hypothalamus stimulates the + Dorsal artery anterior pituitary to secrete FSH and LH. Testosterone also stimulates the Pituitary gland 5 Dorsal nerve libido and the development of secondary sex organs and 5 characteristics.

Corpus spongiosum 6

Corpus cavernosum Deep artery 6 Testosterone has negative Deep fascia 2 FSH stimulates sustentacular feedback effects that reduce GnRH Tunica secretion and pituitary sensitivity cells to secrete androgen-binding 7 Superficial fascia albuginea protein (ABP). to GnRH. LH FSH Inhibin Skin Lacunae

7 Sustentacular cells also secrete inhibin, which selectively inhibits Urethra Median septum FSH secretion and thus reduces Corpus spongiosum sperm production without reducing testosterone secretion. 3 LH stimulates interstitial cells to Ventral secrete testosterone (androgen). Prepuce (b)

2 Key Glans of penis + Testis Sustentacular Stimulation 4 In the presence of ABP, cells + Inhibition testosterone stimulates 4 Testosterone spermatogenesis. External urethral orifice + ABP + (a) Spermatogenesis Interstitial cells + 3 11 12 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Fig. 27.13 Fig. 27.14 Copyright © McGraw-Hill Education. Permission required for reproduction or display.

Meiosis I (first division) Meiosis II (second division) Cross section of seminiferous tubules Lumen of seminiferous tubule Early prophase I Chromosome Prophase II Chromatin condenses to Nucleus Nuclear envelopes form visible chromosomes; disintegrate again; Centromere each chromosome has 2 chromosomes still chromatids joined by a consist of 2 chromatids. Sperm centromere. New spindle forms. Centrioles 5 Metaphase II Spermiogenesis Mid- to late prophase I Chromosomes align on Homologous chromosomes Tetrad equatorial plane. form pairs called tetrads. Chromatids often break Spermatid n n and exchange segments Crossing-over n (crossing-over). Centrioles n produce spindle fibers. Spindle 4 Nuclear envelope fibers disintegrates. Anaphase II Centromeres divide; Meiosis II sister chromatids migrate to opposite Secondary spermatocyte poles of cell. Each chromatid now constitutes n n Metaphase I Centromere a single-stranded Tetrads align on Chromatid chromosome. 3 equatorial plane of cell with centromeres Meiosis I attached to spindle Equatorial fibers. plane Blood–testis barrier Primary Telophase II 2n New nuclear envelopes spermatocyte form around chromosomes; chromosomes uncoil and Sustentacular cell Anaphase I become less visible; Homologous cytoplasm divides. 2 chromosomes separate and migrate to opposite poles of the cell. Type B spermatogonium 2n

Telophase I New nuclear envelopes Tight junction form around Final product is 4 chromosomes; haploid cells with single-stranded cell undergoes 1 cytoplasmic chromosomes. Type A spermatogonium division 2n (cytokinesis). Each cell is Basement membrane now haploid. Cleavage furrow of seminiferous tubule 13 14

Fig. 27.15 Fig. 27.16 Copyright © McGraw-Hill Education. Permission required for reproduction or display. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Golgi complex Bridge to adjacent Acrosome Acrosomal Acrosome vesicle spermatid Nucleus Head Nucleus Head

Axoneme Basal body Mitochondria Basal Midpiece body Mitochondrion of tail Flagellum Excess Midpiece of tail 1 Appearance of cytoplasm Axoneme acrosomal vesicle and flagellum in spermatid 2 Growth of acrosome and flagellum Principal piece of tail Endpiece of tail

Copyright © McGraw-Hill Education. Permission required for reproduction or display. Sexual Stimulation of genital Visual, region, mental, especially stimulation and other glans stimuli Excitement Inactive Internal pudendal Deep artery of penis dilates; erectile nerve tissues engorge with blood; penis guanylate becomes erect

Trabecular muscle of erectile tissues Pelvic nerve cyclase relaxes; allows engorgement of erectile tissues; penis becomes erect Efferent parasympathetic Bulbourethral gland secretes Spinal cord (sacral) signals bulbourethral fluid Nitric oxide Orgasm — emission stage GTP Ductus deferens exhibits peristalsis; sperm are moved into ampulla; ampulla contracts; sperm are moved into urethra

Prostate secretes components of the Active seminal fluid

Efferent Seminal vesicles secrete components of sympathetic guanylate Spinal cord (L1–L2) the seminal fluid signals cyclase Vasodilation Semen in urethra

Afferent signals cGMP and erection

Orgasm — expulsion stage

Efferent Prostate releases additional secretion sympathetic signals Seminal vesicles release additional secretion

Internal urethral sphincter contracts; urine is retained in bladder Spinal cord (L1–S4) Efferent Phosphodiesterase somatic Bulbocavernosus muscle contracts, and signals rhythmically compresses bulb and root of penis; semen is expelled (ejaculation inhibitors occurs) Degraded Loss of Resolution

Internal pudendal artery constricts; reduces blood flow into penis by PDE5 erection

Trabecular muscles contract; Efferent squeeze blood from erectile tissues sympathetic Spinal cord (L1–L2) signals Penis becomes flaccid (detumescent) 17 18