THE PROSTATE

What is the prostate?

The prostate is a small, but important organ (or gland), found in the male reproductive system.  Its main role is to make fluid that protects and feeds sperm.  The prostate makes about half of the fluid that is ejaculated from the penis at the time of sexual climax (orgasm).

The prostate is made up of a number of small glands surrounded by supporting tissue called the stroma.  The small glands in the prostate make the fluid.  The stroma contains some muscle cells, which contract during ejaculation to help move fluid into the urethra.

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Where is the prostate?

The prostate is about the size of a walnut and shaped like a doughnut.  It sits underneath the bladder and surrounds the top part of the urethra, the tube which urine passes through on its way from the bladder to the penis.

This position around the urethra means that as the prostate grows the urethra becomes narrower, sometimes making it difficult for urine to flow through. The prostate may slow or even stop urine passing through.

Pelvic floor muscles support both the bladder and the bowel and stretch from one side of the pelvis to the other.  The prostate lies on these muscles that run from the tailbone at the back to the pelvic bone at the front.  This group of muscles also surrounds the urethra and rectum and helps to stop urine leaking from the bladder.

Because the prostate is located near the rectum (back passage), growth of the prostate can be checked by a rectal examination where a doctor places a gloved finger into the rectum.

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What does the prostate do?

The prostate gland (together with the other accessory glands such as seminal vesicles and Cowper’s glands) makes fluid that is a major part of semen.  Fluids from these glands are mixed with sperm to help the passage of sperm along the ducts (tubes) of the male reproductive system.

To stop semen flowing backwards to the bladder during ejaculation, the internal sphincter muscle at the base of the bladder closes. At ejaculation, the external sphincter at the lower end of the prostate relaxes to release the fluid from the prostate into the urethra.

The outflow of urine from the bladder is controlled by a ring of muscle called the internal sphincter which is located at the base of the bladder. When the internal sphincter is closed, it stops urine and semen leaving the body through the urethra at the same time. At orgasm, this muscle ring closes tightly to stop semen flowing 'backwards' into the bladder. This muscle ring cannot be consciously controlled and is referred to as an involuntary muscle.

The outflow of urine from the penis is controlled by a different muscle layer (external muscle sphincter) that sits underneath the prostate gland in the region referred to as the pelvic floor. Men can voluntarily control the flow of urine by the control of this muscle layer in the pelvic floor. This muscle layer is referred to as a voluntary muscle because it can be consciously controlled.

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Prostate growth

The growth of the prostate gland is controlled by substances called androgens. Androgens are the sex steroids or hormones that are responsible for the development of male characteristics such as hair and beard growth.

The most important androgen in men is testosterone. Testosterone is produced mainly in the testes by Leydig cells which lie between the sperm producing tubes (seminiferous tubules). Small amounts of testosterone are also made by the adrenal glands which are walnut sized glands that sit on top of the kidneys.

Testosterone is carried in the blood stream to other parts of the body to act on a number of other organs. Only those parts of the body which have sensors that detect androgens (androgen receptors) will respond to testosterone. Testosterone is changed to another androgen called dihydrotestosterone (DHT) which is the androgen that stimulates prostate growth.

Testosterone is not produced until puberty and therefore the prostate gland remains small before puberty. The rising levels of testosterone at puberty cause the prostate gland to increase in size and continue to grow during adult life and in ageing men. If testosterone levels are lowered by removal of the testes, the prostate shrinks in size. Without testosterone, the prostate will also stop producing fluid because the prostate cells depend on testosterone for this function.

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