Male Reproductive System Anatomy and Physiology

The scrotum houses and protects the testes, epididymis, and ductus deferens.
It also contains blood vessels (testicular artery and vein), a venous plexus, lymphatics, and nerves.

The scrotum, testes, and surrounding structures maintain a specific temperature for sperm production.
Sperm develop at approximately 2 degrees Celsius lower than internal body temperature.
Internal body temperature is around 37 degrees Celsius, while sperm require about 35 degrees Celsius.

Cremaster Muscle:
- A deep muscle within the scrotum.
- Contracts to draw the testes closer to the body when it's cold.
- Relaxes to allow the testes to suspend further from the body when it's warm.
Dartos Muscle:
- Controls the wrinkling of the scrotum skin.
- Contracts when cold to reduce surface area and heat loss.
- Holds the testes closer to the body to maintain temperature.
Pampiniform Plexus:
- A countercurrent heat exchange mechanism.

Involves an artery and a network of veins adjacent to each other with blood flowing in opposite directions.
Warm blood at 37 degrees Celsius comes from the abdomen/pelvis through the testicular artery.
The venous plexus wraps around the spermatic cord and artery.
As warm arterial blood descends, the pampiniform plexus removes heat, transferring it to the venous system.
This cools the arterial blood as it descends, maintaining a temperature of approximately 35 degrees Celsius for sperm production.

Testes:
- Contain the germinal epithelium where sperm are produced.
- Seminiferous tubules are located within lobules.
- Supporting cells produce hormones (testosterone, inhibin), nutrients, and remove waste products.
Efferent Ductules:
- Sperm move from the seminiferous tubules into the rete testis.
- Then, they proceed to the efferent ductules.
Epididymis:
- A tightly coiled tube (approximately 18 feet long) for sperm maturation and storage.
- Sperm can be housed for about 40-60 days.
- It takes about 20 days for sperm to reach the tail of the epididymis.
- Un-ejaculated sperm are reabsorbed and replaced.
- Ejaculate contains 50-200 million sperm in 2-5 milliliters of fluid.
Ductus Deferens (Vas Deferens):
- The epididymis makes a hairpin turn and becomes the ductus deferens.
- It ascends the spermatic cord, passes over the pubic symphysis, and runs lateral to the bladder.
- Posterior to the bladder, it's adjacent to the seminal vesicles.
- Forms the ejaculatory duct within the prostate.

Inferior to the bladder.
Produces 20-30% of semen.
Prostate cancer is the second leading cause of cancer in men.
- About 9% of men will develop prostate cancer.
- Can be genetic.
Benign Prostatic Hypertrophy (BPH):
- Non-cancerous excessive growth of the prostate.
- Can compress the urethra, limiting urination.
- BPH is common with age and may or may not require treatment.
Progression of Prostate cancer:
- Prostate cancer can metastasize.
- Early detection is crucial, as it often begins in the periphery.
- Constriction of the urethra can cause urine backup, leading to bladder and kidney infections.

Located at the base of the penis, adjacent to the membranous urethra.
Produce about 10% of secretions.
Secrete a clear, slippery fluid to lubricate the head of the penis.
Protect sperm from the acidic environment of the urethra.
Create a path of least resistance for sperm migration through the female reproductive system.

Fluid ejaculated, containing sperm.
Composed of: $\sim$ 60% seminal vesicle fluid, 20-30% prostatic secretions, a small amount of bulbourethral gland secretions, and ~10% sperm.
10% of semen composed of 50-200 million sperm in 2-5 milliliters of fluid.
Many sperm are anatomically incorrect or non-motile.