The Male Reproductive System: Anatomy and Physiology

Know the structures, where they sit, and what each one secretes. Here is the working anatomy and physiology of the male reproductive system.

Internal Structures

Epididymis

• A tightly coiled tube that carries sperm from the tubule to the vas deferens.
• Approximately 20 feet long.
• Stores some sperm along with semen.
• Sperm travel the epididymis over an estimated 12 to 20 days and reach maturity at 64 days total.

Vas Deferens

• Carries sperm through the inguinal canal from the epididymis into the abdominal cavity, ending at the seminal vesicles and ejaculatory duct.
• A hollow tube with a thick fibrous coating, surrounded by arteries and veins.

Seminal Vesicles

• Two convoluted pouches along the lower posterior surface of the bladder.
• Secrete a viscous, alkaline liquid high in protein, sugar, and prostaglandins that increases sperm motility.

Ejaculatory Ducts

• Pass through the prostate gland to join the seminal vesicles and the urethra.

Prostate Gland

• A chestnut-sized gland below the bladder.
• Secretes a thin, alkaline fluid that protects sperm from the low pH of the urethra.
• The urethra passes through its center like a doughnut.

Bulbourethral Glands

• Also called Cowper's glands, they secrete alkaline fluid to counter the acidic urethral environment.
• Two glands sit on either side of the prostate gland and seminal vesicles, emptying through short ducts into the urethra.
• Semen is 60% from the prostate gland, 30% from the seminal vesicles, 5% from the epididymis, and 5% from the bulbourethral glands.

Urethra

• Passes through the prostate gland toward the shaft and glans penis.
• A hollow tube from the base of the bladder, lined with mucous membrane.
• Approximately 8 inches or 18 to 20 cm long.

External Structures

Scrotum

• Supports the testes and regulates sperm temperature.
• A rugated, muscular, skin-covered pouch over the perineum.
• To protect sperm production and viability, it contracts toward the body in cold weather and relaxes away from the body in heat.

Testes

• Two oval-shaped glands sit in the scrotum.
• Each is 2 to 3 cm wide, encapsulated in a protective white fibrous capsule.
• Each testis contains several lobules, with Leydig's cells producing testosterone and seminiferous tubules producing spermatozoa.
• In most men one testis sits slightly lower than the other to avoid trauma during sitting or muscular activity.

Penis

• Three parts: two corpus cavernosa and one corpus spongiosum.
• The erectile tissues carry the urethra, so the penis serves both urinary and reproductive functions.
• Erection is driven by parasympathetic innervation; blood supply comes from the penile artery.
• The glans, a sensitive bulging ridge of tissue, sits at the distal end.
• The prepuce, a retractable casing of skin, covers the glans at birth and is the part removed during circumcision.