Male Reproductive System Male Reproductive System The Scrotum

Male Reproductive System

Male Reproductive System

The Scrotum • Sac of skin that hangs outside the abdominopelvic cavity at the root of the penis • Contains paired testicles separated by a midline septum • Its external positioning keeps the testes 3 C lower than core body temperature (needed for sperm production) • When external temperature is very cold, the scrotum becomes wrinkled as it is pulled closer to the warmth of the body wall

The Testes • Each testis is divided into 250 -300 lobules, each containing 1 -4 seminiferous tubules • Seminiferous tubules produce the sperm stimulated by FSH released by pituitary • Interstitial cells around the tubules produce androgens (testosterone) – stimulated by LH released by pituitary • Once the sperm are made, they continue to the epididymis

The Testes

The Epididymis • First part of male duct system • Provides a temporary storage site for the immature sperm cells – Trip through takes about 20 days – Sperm learn how to swim here! • When a male is sexually stimulated, the walls of the epididymis contract to propel sperm into the ductus deferens

Ductus Deferens and Ejaculatory Duct • Propels sperm from the epididymis up into the pelvis, and back down to join up with the urethra • Also called the vas deferens • During an ejaculation, smooth muscles around the duct contract to create peristaltic waves that squeeze the sperm forward • Vasectomy – cutting and ligating the ductus deferens, which is a nearly 100% effective form of birth control

Ductus Deferens and Ejaculatory Duct

Vasectomy

The Penis • A copulatory organ designed to deliver sperm into the female reproductive tract • Consists of an attached root and a free shaft that ends in the glans penis • Prepuce, or foreskin – cuff of skin covering the distal end of the penis – Circumcision – surgical removal of the foreskin after birth

The uncircumcised penis. The penis immediately after circumcision. The appearance of the circumcised penis after healing is complete.

The Penis • Internal penis includes the urethra (which carries both semen and urine) and three cylindrical bodies of erectile tissue • Erectile tissue – spongy network of connective tissue and smooth muscle riddled with vascular spaces; assists with erection and ejaculation • Erection – during sexual excitement, the erectile tissue fills with blood causing the penis to enlarge and become rigid (which makes penetration easier)

The Penis

Accessory Glands: Seminal Vesicles • Lie on the posterior wall of the bladder and secretes 60% of the volume of semen • Join the ductus deferens to form the ejaculatory duct • Sperm and seminal fluid mix in the ejaculatory duct and enter the urethra during ejaculation

Accessory Glands: Seminal Vesicles

Accessory Glands: Prostate Gland • Doughnut-shaped gland that encircles part of the urethra inferior to the bladder • Its milky fluid, which contains citrate (Vitamin C), enzymes, and prostate-specific antigen (PSA), accounts for one-third of the semen volume • Fluid helps to activate sperm • Fluid made enters the urethra during ejaculation

Accessory Glands: Prostate Gland

Accessory Glands: Bulbourethral Glands (Cowper’s Glands) • Pea-sized glands inferior to the prostate • Produce thick, clear mucus prior to ejaculation that neutralizes traces of acidic urine in the urethra

Accessory Glands: Bulbourethral Glands (Cowper’s Glands)

Semen • Milky white, sticky mixture of sperm and accessory gland secretions • Provides a transport medium and nutrients (fructose), protects and activates sperm, and facilitates their movement • Prostaglandins in semen: – Decrease the viscosity of mucus in the cervix – Stimulate reverse peristalsis in the uterus – Facilitate the movement of sperm through the female reproductive tract

Semen • Sperm are most active at neutral p. H, and can even die off at p. H of 4 and below! • However, vaginal p. H is normally 3. 5 -3. 9! • Seminal fluid and prostate gland fluid has a p. H of 7. 27. 6, which will help to neutralize out the vagina… but this doesn’t last forever! • p. H in vagina will drop back down to 4. 0 within 8 hours – so the lifetime of sperm in the vaginal canal is 8 hours max; lifetime in the uterus and fallopian tubes is about 48 hours • Only 2 -5 m. L of semen are ejaculated, but it contains 50 -130 million sperm per m. L

Sperm • Sperm have three major regions – Head – contains DNA and has a helmetlike acrosome containing hydrolytic enzymes that allow the sperm to penetrate and enter the egg – Midpiece – contains mitochondria spiraled around the tail filaments – Tail – a typical flagellum produced by a centriole

Spermiogenesis: Spermatids to Sperm

Secondary Male Characteristics • Deeper voice due to enlarged larynx • Increased hair growth over body, especially in axillary and pubic regions, as well as on face • Enlargement of skeletal muscles • Increased heaviness of bones • Long, narrow pelvis • All are due to testosterone levels