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The male reproductive system is essential for sperm production and delivery. It includes key structures such as the scrotum, which maintains the testes at a cooler temperature vital for viable sperm. The testes produce sperm within seminiferous tubules and secrete testosterone. Sperm travels through the epididymis, ductus deferens, and the ejaculatory duct before being expelled through the penis. Accessory glands contribute fluids for nourishment and protection. Understanding these components offers insight into male reproductive health and physiology.
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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 3C 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 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
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)
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: 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: 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
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 pH, and can even die off at pH of 4 and below! • However, vaginal pH is normally 3.5-3.9! • Seminal fluid and prostate gland fluid has a pH of 7.2-7.6, which will help to neutralize out the vagina… but this doesn’t last forever! • pH 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 mL of semen are ejaculated, but it contains 50-130 million sperm per mL
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
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
The Ovaries • Paired organs on each side of the uterus held in place by several ligaments • About the size & shape of almonds • Embedded in the ovary are follicles
Follicles • Each follicle consists of an immature egg called an oocyte • Oocytes are surrounded by layers of follicle cells, which will mature – because of FSH released from pituitary • When follicle is mature, the developing egg (ova) will be released (ovulation) – stimulated by LH released from pituitary • After ovulation, the ruptured follicle is called a corpus luteum, which eventually degenerates
A picture of ovulation, as captured during a hysterectomy surgery!
A note about oocytes… • Females are born with approximately 700,000 oocytes at birth combined in the two ovaries… this is the lifetime supply, and no more will develop • The number already decreases down to 400,000 by puberty, and only about 500 eggs will be released during a woman’s lifetime • This is different than in the males, where sperm continue to be produced throughout the reproductive lifetime
Uterine (Fallopian) Tubes • Each tube is about 10 cm long and 1 cm in diameter • Allows egg (ova) to travel from ovary to uterus • Usually the site of fertilization • End of tube near the ovary expands to form a funnel-shaped infundibulum, which has finger-like extensions (fimbriae)
Uterine (Fallopian) Tubes • The uterine tubes have no contact with the ovaries and the ovulated ovais cast into the peritoneal cavity • Beating cilia on the fimbriae create currents to carry the ova into the uterine tube • The ova is carried toward the uterus by peristalsis and ciliary action
Ectopic Pregnancy • While ova get fertilized in the uterine tubes, the egg should not implant here! • If the egg is implanted anywhere other than the uterus, this is called an ectopic pregnancy • 98% of ectopic pregnancies occur in the uterine tubes • Most will resolve themselves naturally through a miscarriage, but sometimes surgery is required to remove the fetus or internal bleeding can occur
Uterus • Hollow, thick-walled organ located in the pelvis anterior to the rectum and posterosuperior to the bladder • Where implantation of fertilized ova occurs • About the size and shape of a pear • Body – major portion of the uterus • Fundus – rounded region superior to the entrance of the uterine tubes • Cervix – narrow neck which projects into the vagina inferiorly
Uterine Wall • Wall composed of three layers • Perimetrium – outermost serous layer; the visceral peritoneum • Myometrium – middle layer; interlacing layers of smooth muscle; contracts during childbirth • Endometrium – mucosal lining of the uterine cavity
Endometrium • If fertilization occurs, the fertilized egg burrows into the endometrium and resides there for the rest of development • When a woman is not pregnant, the endometrial lining sloughs off periodically (approximately every 28 days) in response to hormone levels
Vagina • Thin-walled tube about 3 to 4 inches long extending from the cervix to the exterior of the body • The urethra is embedded in the anterior wall • Provides a passageway for male penetration, birth, and menstrual flow • The labial folds protect the vaginal opening and the urethral opening
External Genitalia • Clitoris (homologous to the penis) • Erectile tissue that become swollen with blood during sexual excitement • Greater vestibular glands • Secretions lubricate the distal end of the vagina during intercourse
Monthly Female Cycles • Include the Ovarian Cycle and the Menstrual Cycle
Ovarian Cycle • Monthly series of events associated with the maturation of an egg • Follicular phase – period of follicle growth (days 1–14) – due to FSH; causes production of estrogen • Ovulation occurs midcycle due to LH • 1-2% of ovulations release more than one ova, which if both fertilized, results in fraternal t • Luteal phase – period of corpus luteum activity (days 14–28)
