The Reproductive System Chapter 27 The Reproductive System

Primary sex organs (gonads) Reproductive System Primary sex organs (gonads) Testes in males Ovaries in females Gonads produce: Sex cells called gametes Secrete sex hormones Accessory reproductive organs: Ducts Glands External genitalia

Reproductive System Sex hormones: They play roles in: Androgens (males) Estrogens & progesterone (females) They play roles in: Development of the reproductive organs Function of the reproductive organs Sexual behavior and drives Growth and development of many other organs and tissues

Male Reproductive System The male gonads (testes): Lie within the scrotum Produce sperm Sperm: Delivered through a duct system consisting of: Epididymis Ductus deferens Ejaculatory duct Urethra

Male Reproductive System Accessory sex glands: Empty their secretions into the ducts during ejaculation Include : Seminal vesicles Prostate gland Bulbourethral glands

Male Reproductive System Figure 27.1

Sac of skin and superficial fascia The Scrotum Sac of skin and superficial fascia Hangs outside the abdominopelvic cavity Contains testicles separated by a midline septum Its external positioning keeps the testes: 3C lower than core body temperature: Needed for sperm production

Intrascrotal temperature is kept constant by two sets of muscles: The Scrotum Intrascrotal temperature is kept constant by two sets of muscles: Dartos muscle: Smooth muscle Wrinkles scrotal skin (cold) Cremaster muscle: Bands of skeletal muscle Elevate the testes (cold)

The Scrotum S7 Figure 27.2

Each testis is surrounded by two tunics: The Testes Each testis is surrounded by two tunics: The tunica vaginalis (serous), derived from the peritoneum The tunica albuginea, the fibrous capsule of the testis Septa divide the testis into 250-300 lobules Each lobule contains 1-4 seminiferous tubules

The Testes Seminiferous tubules: Tubulus rectus: Where sperm are produced Converge to form the tubulus rectus Interstitial (Leydig) cells surround seminiferous tubules These cells produce androgens Tubulus rectus: Straight tubules that convey sperm to the rete testis From the rete testis, the sperm: Leave the testis via efferent ductules Enter the epididymis

The Testes Figure 27.3a

The Testes Testicular arteries: Testicular veins: Spermatic cord: abdominal aorta branch supply the testes Testicular veins: arise from the pampiniform plexus Spermatic cord: A connective tissue sheath Encloses: Nerve fibers, blood vessels, and lymphatics that supply the testes

The Penis A copulatory organ designed to: Consists of: Deliver sperm into the female reproductive tract Consists of: An attached root A free shaft The glans penis Prepuce, or foreskin: Cuff of skin covering the distal end of the penis Circumcision: Surgical removal of the foreskin after birth

Internally the penis contains: The spongy urethra Three cylindrical bodies (corpora) of erectile tissue Erectile tissue is made of: Spongy network of connective tissue Smooth muscle riddled with vascular spaces

The Penis Erection: Corpus spongiosum: Occurs during sexual excitement The erectile tissue fills with blood causing the penis to: Enlarge Become rigid Corpus spongiosum: The midventral erectile body Surrounds the urethra Expands to form: Proximally, the bulb of the penis Distally, the glans penis

The Penis Corpora cavernosa: Crura: The paired dorsal erectile bodies Bound by fibrous tunica albuginea Crura: Proximal penile end Surrounded by the ischiocavernosus muscle Anchors the penis to the pubic arch

The Penis Figure 27.4

Epididymis Has three regions: Head: Head Body Tail Joins the efferent ductules Caps the superior aspect of the testis Entering nonmotile sperm, become motile while passing through its tubes Expels sperm into ductus deferens when contract during ejaculation

Ductus Deferens and Ejaculatory Duct Runs from the epididymis through the inguinal canal into the pelvic cavity Its terminus expands to form the ampulla Joins the duct of the seminal vesicle to form the ejaculatory duct Propels the sperm to the urethra Vasectomy: Cutting & ligation of the ductus deferens Nearly 100% effective means of male birth control Success rate of reversing the procedure is 50%

Conveys both urine and semen in males Consists of three regions Urethra Conveys both urine and semen in males Consists of three regions Prostatic urethra: Portion surrounded by the prostate Membranous urethra: Lies in the urogenital diaphragm Spongy, or penile urethra: Runs through the penis Opens to the outside at the external urethral orifice

Accessory Glands: Seminal Vesicles Paired glands Lie on the posterior wall of the bladder Produces and stores secretion that is: Yellowish viscous fluid Contains: Ructose A coagulating enzyme “vesiculase” Ascorbic acid Prostaglandins & other substances

Accessory Glands: Seminal Vesicles (cont’d) Secrete 70% of the volume of semen: Ducts join ductus deferens forming ejaculatory ducts Sperm & seminal fluid mix in the ejaculatory duct Semen enter the prostatic urethra during ejaculation

Accessory Glands: Prostate Gland Doughnut-shaped single gland Encircles the urethra just inferior to the bladder Produces milky, slightly acid fluid that: Contains citrate, enzymes, prostate-specific antigen (PSA) Accounts for one-third of the semen volume Plays a role in the activation of sperm Enters the prostatic urethra via several ducts during ejaculation

Accessory Glands: Bulbourethral Glands (Cowper’s Glands) Pea-sized paired glands Inferior to the prostate Produce (prior to ejaculation): Thick, clear mucus Secreted mucus: Neutralizes traces of acidic urine in the urethra

Semen Milky, viscous, sticky, white, alkaline fluid A mixture of sperm and accessory gland secretions Contains fructose, ascorbic acid, coagulating enzyme (vesiculase), and prostaglandins Provides a transport medium and nutrients (fructose) Protects and activates sperm, and facilitates their movement Prostaglandins in semen: Facilitate sperm movement through the female reproductive tract by: Decreasing the viscosity of mucus in the cervix Stimulating reverse peristalsis in the uterus

Male Sexual Response: Erection Enlargement & stiffening of the penis Results from engorgement of erectile tissue with blood A parasympathetic reflex promotes the release of nitric oxide (NO) during sexual arousal NO causes erectile tissue to fill with blood (vasodilatation) Blood-expanded corpora cavernosa compress their drainage veins retarding blood outflow Retarded blood maintains engorgement The corpus spongiosum keeps the urethra open during ejaculation Impotence: Inability to attain erection

Ejaculation Is the propulsion of semen from the male duct system At ejaculation, sympathetic nerves serving the genital organs cause: Reproductive ducts and accessory organs to contract and empty their contents The bladder sphincter muscle to constrict, preventing the expulsion of urine Bulbospongiosus muscles to undergo a rapid series of contractions Propulsion of semen from the urethra

Human Life Cycle Figure 27.5

Spermatogenesis The sequence of events that produces sperm in the seminiferous tubules of the testes Each cell has two sets of chromosomes (a maternal & a paternal) Such cell is said to be diploid (2n chromosomal number) Humans somatic cells have 23 pairs of homologous chromosomes Gametes “ reproductive cells” only have 23 chromosomes and are said to be haploid (n chromosomal number) Gamete formation is by meiosis During meiosis the number of chromosomes is halved (2n to n)

Mitosis of Spermatogonia Spermatogenesis: Begins at puberty Spermatogonia (stem cells): Are the outermost cells In contact with the epithelial basal lamina Each mitotic division results in: Type A and type B daughter cells

Mitosis of Spermatogonia Type A cells: Remain at the basement membrane Maintain the germ line Type B cells: Move toward the lumen Become primary spermatocytes

Spermatocytes to Spermatids Primary spermatocytes: Undergo meiosis I, forming two haploid cells called: Secondary spermatocytes Secondary spermatocytes: Undergo meiosis II forming daughter cells called: Spermatids Spermatids are: Haploid Nonmotile Small round cells with spherical nuclei Seen close to the lumen of the tubule

Figure 27.8b, c

Semen Contains the following substances: The hormone relaxin which enhances sperm motility The antibiotic seminalplasmin which destroys certain bacteria Clotting factors that coagulate semen immediately after ejaculation (stick to vaginal wall & not being drained out) Fibrinolysin that liquefies the sticky mass (resume movement) Semen alkalinity neutralizes the acid environment in the male urethra and female vagina Ejaculated amount of semen is only 2-5 ml, but contains 20-150 million sperm/ml