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Men's sexual anatomy 2: The testicles, epididymis and other sexual glands

 

This page describes the internal parts of men's sexual organs: the testicles, epididymis, prostate, Cowper's glands and seminal vesicles.

 

Testicles

The testicles have many names: balls colloquially, testes, or even gonads. (When we talk about testes, one of them is referred to as a testis, the singular form which goes back to the good old Latin name).

The testicles are two paired glands which sit in the scrotum and mostly produce sperm and testosterone.

Each testis is about 5 cm long and 2.5 cm thick with an oval shape. The testicles form originally in the abdominal wall during development and descend into their space in the scrotum just before birth. Each testicle sits in a dense fibrous capsule, the tunica albuginea, the inward extensions of which divide the testicle into lobes.

Each of the two to three hundred lobes has a few tightly coiled tubules called the seminiferous tubules, where the sperm are produced.

In between the tubules sit the Leydig cells, which secrete testosterone, the most important male sex hormone. All the tubules eventually lead to a duct, which allows sperm and fluid to leave the testicles via the epididymis.

 

Epididymis and Vas deferens

The epididymis is a small, about 4 cm long, comma-shaped organ that sits on the back of each testicle. It consists of a long thin tube, which is tightly wound up. Straightened out the tube would measure more than 6 meters in length!

The epididymis stores sperm; it's also the place where sperm develop their motility (ability to move around). Sperm can be stored in the epididymis for more than a month.

The end of the epididymis leads on to the vas deferens, the duct that carries sperm and fluid from the scrotum into the body cavity, up and around the bladder to the prostate. It broadens at its end (the ampulla) to be able to store sperm, which can survive in the vas deferens for a few months.

 

 

Seminal vesicles

These are the first of three sets of accessory sex glands in the human male. The seminal vesicles lie just to the front of the bladder, above the prostate, and their outgoing tube joins the vas deference at its very end in the prostate. Each seminal vesicle is about 5 cm long.

The seminal vesicles produce 60% of the fluid volume of semen with different biological components. They produce an alkaline, viscous fluid, which also contains fructose (a sugar), prostaglandins and clotting proteins.

The alkaline fluid is required to neutralize the acidic environment of the male urethra and the female reproductive system as sperm would not be able to survive these acidic environments.

Fructose becomes the energy source for sperm, which they need to survive and move around. Should you be interested in penis pictures to see the variation in appearance between men, check this out.

 

Prostate gland

The prostate gland is the next gland through which the sperm pass on their onward journey. It's a small, chestnut-sized organ at the bottom of the bladder.

It's shaped like a thick ring around the urethra, the tube through which a man passes urine away from the bladder.

The prostate secrets a milky, slightly acidic fluid which supports the health and mobility of sperm. 25% of the volume of semen is made up by the prostate's secretions. 

The prostate gland slowly increases in size during childhood and than expands more quickly during puberty. Its size should remain more or less stable during adulthood, but it may start to enlarge again in older men.

This may lead to the prostate putting pressure on the urethra, the tube which allows one to pass urine from the bladder to the tip of the penis. Obviously, the extra pressure isn't good for peeing and may lead to dribbling and poor stream. 

 

Cowper's glands

These small, pea-sized glands are located below the prostate and are also called bulbourethral glands. There are two of them, and their outgoing ducts lead into the urethra.

Cowper's glands secret a sticky, alkaline fluid during sexual arousal, which neutralizes the acidity of the male urethra.

Additionally, they also secret a mucus substance (you may know this as "pre-cum"), which acts as a natural lubricant for the tip of the penis. The quantity of pre-cum in any episode of sex varies between a small droplet and 5 ml, with some men not being aware of producing any at all.

This fluid may already contain some live sperm, released before ejaculation, which is why it is essential to put on a condom for birth control prior to penetration, not just before ejaculation.

 

Other related topics:

Source for the facts cited in this page: 

ABC of Sexual Health (2005) Second edition edited by John M Tomlinson, British Medical Journal Books and Blackwell Publishing.

Principles of anatomy and physiology (2000) Ninth edition by Gerard J. Tortora and Sandra Reynolds Grabowski. Publishers: John Wiley and Sons


 

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