A normal-sized prostate fits neatly into the crowded, multi-functional area of the man's lower pelvis.
The prostate in men, like the breast in a woman, is a gland that produces and secretes fluid and controls the flow of fluid. Cells lining the prostate gland make some of the semen that comes out of the penis at the time of sexual climax (orgasm).
Prostate-specific antigen (PSA) helps to keep the semen in its liquid form. It is an enzyme in the form of a glycoprotein produced primarily by cells lining the acini and ducts of the prostate gland.
A normal human male prostate is about the size of a small plum. The prostate sits above the base of the penis below the urinary bladder and backs onto the front wall of the rectum.
The prostate evolved in this tight-wedged position to aid reproduction. The prostate makes some of the fluid for semen, may keep urine out out of the semen, and enhances pleasurable sensations of arousal and orgasm.
1: Vas deferens
2: Seminal vesicle
3: Base of the prostate
4: Apex of the prostate
5: Prostatic urethra
In males a single pipe, the urethra, serves two functions, urination and ejaculation. The urethra runs from the bladder through the prostate to the tip of the penis. The section that runs through the prostate is called the prostatic urethra.
The prostate gland makes almost a third of the fluid in the semen that a man ejaculates.
During ejaculation millions of sperm arrive in the prostatic urethra. The sperm are made in the testicles. Leading from each testis is a coiled mass of spermatic ducting called the epididymis (Greek: upon + testicle), which houses maturing sperm. The epididymis (below left) looks like the crest on a helmet. It connects to a tube called the vas deferens (Latin: carrying-away vessel).
Sperm lodge in the epididymis for several days. When sexual excitement triggers ejaculation, muscle contractions in the wall of the vas deferens suck the sperm from the epididymis through to the vas deferens. As muscle contractions continue in waves the sperm rocket up towards and around the bladder and down by the two seminal vesicles into the prostatic urethra.
1: Epididymis attached to a testis
2: Head of epididymis
3: Lobules of epididymis
4: Body of epididymis
5: Tail of epididymis
6: Duct of epididymis
7: Deferent duct (ductus deferens or vas deferens ) the tail of the epididymis, via the vas deferens, to the urethra in the penis. As sperm pass through the different tubes, fluid from the seminal vesicles, Cowper's and prostate glands is added to the sperm. The mixture is then called semen. Over 90% of the semen is produced from the prostate and seminal vesicles and not from the testis.
Some of the prostate is made of muscle. When sperm reach the prostatic urethra the prostate contracts, This may pinch a duct to the bladder so that sperm are kept urine-free. The contraction helps secrete prostatic fluid into the urethra and may also help expel the ejaculate.
Fluids from the prostate, the seminal vesicles and Cowper's glands make up the biulk of semen. They flow into the prostatic urethra around the sperm. The semen is propelled along the urethral tube and out of the penis.
Protect and Nourish
The fluids in semen makes a protective sea to nourish the sperm and protect them from the acidic environment of the female vagina.
"The vagina is mildly acidic (~pH 4), sufficiently acidic to protect against many types of pathogens. But sperm are acid-sensitive, so semen is alkaline and the ejaculate abolishes the protective acidity of the vagina for many hours after intercourse. Otherwise sperm would be killed within seconds by vaginal acidity." Richard A. Cone. See his lab's webpage.
- Cowper's gland fluid lubricates the urethra.
- Seminal vesicle secretions are rich in fructose (an energy source for sperm), prostaglandins (from fatty acids) and proteins that help clot the semen in the female vagina.
- Prostate secretions are rich in calcium, zinc, citric acid, acid phosphatase, albumin, and prostatic specific antigen (PSA). In normal prostatic fluid citrate is high. A recent study finds that citrate is more than twice as low in prostate fluid of men with prostate cancer than in men without prostate cancer. Prostatic fluid gives semen its milky color.
The prostate has the highest concentration of citrate of any tissue in the human body. Scientsists say they don't really know why this is, or what it does. They believe it has a role in reproduction, as yet unknown.
Zinc is also found in the prostate at high concentrations. Zinc is used as an antiseptic in everything from diaper rash ointment to cold remedies. Scientists think it has some role in fighting bacterial infection in the prostate.
The PSA in prostatic fluid, at the appropriate time, undoes the effect of the clotting enzyme derived from seminal vesicle fluid. The clotting enzyme makes the ejaculate gel and "glues" the semen in place by the female's cervix in her vagina. For a few minutes the sperm stay inside this gel. With 15 to 30 minutes PSA enzyme in the semen dissolves the clot and frees the sperm to swim into the uterus.
"This has an obvious advantage in reproduction. The sperm are in the best place to increase the chances of fertilisation." (The Prostate Cancer Charity, Prostatic Fluid)
Unfortunately, the prostate's brilliant wrap-around structure with dual-purpose core tubing can become a liability if the prostate swells or enlarges.This may happen in a man of any age from a prostate infection (prostatitis). In middle age and beyond, after the male reproductive peak has passed, the prostate may become troublesome as a result of benign growth (BPH). An inflamed or benignly overgrown prostate can cause discomfort and pain and interfere with urination.
Even more seriously, a prostate in which some cells are cancerous can threaten a man's health and eventually his life.
Sources and Links
Gray's Anatomy Illustrations (
Henry Gray (1825-1861). Anatomy of the Human Body. 1918.) online at bartleby.com and at wikipedia.org
Find Life-Threatening Prostate Cancer by Measuring PSA Velocity During "Window of Curability" Nov 1, 2006.
This page made by J. Strax December 26, 2006. Last updated December 26, 2008.