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.
Frequently Asked Questions
What are the main parts of the male reproductive system? The internal structures are the testes, epididymis, vas deferens, seminal vesicles, ejaculatory ducts, prostate gland, and bulbourethral glands. The external structures are the penis and the scrotum (StatPearls).
Where is sperm produced? Sperm form in the seminiferous tubules of the testes through spermatogenesis. The Leydig (interstitial) cells between the tubules produce testosterone, the main male sex hormone.
How long does sperm take to mature? Sperm spend roughly 12 days moving through the coiled epididymis, where they gain motility, and full development from spermatogonia to mature spermatozoa takes about 64 days (StatPearls).
What does the prostate gland do? The prostate secretes a thin, alkaline fluid that mixes into semen and helps protect sperm from the acidic environment of the urethra and vagina. The urethra runs through its center.
Why do the testes sit outside the body? Sperm production needs a temperature slightly below core body temperature. The scrotum regulates this by contracting to pull the testes closer in cold and relaxing to lower them in heat.