The prostate (from Greek προστάτης - prostates, literally "one who stands before", "protector", "guardian") is a compound tubuloalveolar exocrine gland of the male mammalian reproductive system. Women do not have a prostate gland, although women do have microscopic paraurethral Skene's glands connected to the distal third of the urethra in the prevaginal space that are homologous to the prostate.
The prostate differs considerably among species anatomically, chemically, and physiologically.
The main function of the prostate is to store and secrete a clear, slightly alkaline (pH 7.29) fluid that constitutes 10-30% of the volume of the seminal fluid that, along with spermatozoa, constitutes semen. The rest of the seminal fluid is produced by the two seminal vesicles. The alkalinity of seminal fluid helps neutralize the acidity of the vaginal tract, prolonging the lifespan of sperm. The prostatic fluid is expelled in the first ejaculate fractions together with most of the spermatozoa. In comparison with the few spermatozoa expelled together with mainly seminal vesicular fluid those expelled in prostatic fluid have better motility, longer survival and better protection of the genetic material (DNA).
The prostate also contains some smooth muscles that help expel semen during ejaculation.
Prostatic secretions vary among species. They are generally composed of simple sugars, and are often slightly alkaline.
In human prostatic secretions, the protein content is less than 1% and includes proteolytic enzymes, prostatic acid phosphatase, and prostate-specific antigen. The secretions also contain zinc with a concentration 500-1,000 times the concentration in blood.
To work properly, the prostate needs male hormones (androgens), which are responsible for male sex characteristics.
The main male hormone is testosterone, which is produced mainly by the testicles. Some male hormones are produced in small amounts by the adrenal glands. However, it is dihydrotestosterone that regulates the prostate.
The prostatic part of the urethra develops from the pelvic (middle) part of the urogenital sinus (endodermal origin). Endodermal outgrowths arise from the prostatic part of the urethra and grow into the surrounding mesenchyme. The glandular epithelium of the prostate differentiates from these endodermal cells, and the associated mesenchyme differentiates into the dense stroma and the smooth muscle of the prostate. The prostate glands represent the modified wall of the proximal portion of the male urethra and arises by the 9th week of embryonic life in the development of the reproductive system. Condensation of mesenchyme, urethra and Wolffian ducts gives rise to the adult prostate gland, a composite organ made up of several glandular and non-glandular components tightly fused within a common capsule.
Skene's glands found in many females are homologous to the prostate gland in males.
A healthy human prostate is slightly larger than a walnut. It surrounds the urethra just below the urinary bladder and can be felt during a rectal exam.
The ducts are lined with transitional epithelium.
Within the prostate, the urethra coming from the bladder is called the prostatic urethra and merges with the two ejaculatory ducts. (The male urethra has two functions: to carry urine from the bladder during urination and to carry semen during ejaculation.) The prostate is sheathed in the muscles of the pelvic floor, which contract during the ejaculatory process.
Should I be screened for prostate cancer?
Men who are screened run some risks from the biopsy test, and may not benefit from treatment even if they do have cancer.
In fact, by diagnosing and treating cancers that might not need to be treated, the risk of reduced quality of life from treatment complications may be higher than if they were not screened.
This does not stop men asking to be screened and a test (the PSA test) is available if you request it. However, the National Health Committee considers that you should make sure you are fully informed of all the issues before going ahead with the test.
You may know or have heard of someone who swears by the PSA test (for more on this see Screening tests heading below). However there are a number of factors that mean the test would not be helpful to everyone.
A number of studies weighing up the effectiveness of screening and treatment against "watchful waiting" (waiting to see how the disease develops) are in progress.
Right now there is no evidence that screening a man without symptoms will help him to live longer.
If you feel well but have some concerns about prostate cancer, or if you have symptoms, a discussion of the options will help you decide on a course of action.
The things to be considered are any family history of cancer, your age, your general health and how a diagnosis of cancer may affect you.
Your doctor can advise you of the potential risks and benefits of being screened, and also of the treatment options for cancer if it was to be detected. It is possible that you might not be seriously affected, even if you have cancer.
However, the National Health Committee advises men who have noticed any changes or problems with their urinary function to consult their doctor without delay.
Possible symptoms include difficulty starting to pass urine, a slow flow, dribbling, blood in the urine, having to get up often at night, or having to rush to get to the toilet. Remember that these symptoms can be caused by a number of medical problems.
What is prostate cancer?
Prostate cancer is a cancer that develops in the prostate gland. The prostate sits just below the bladder and is about the size of a walnut. Problems begin when the gland grows bigger, which commonly happens as you get older.
Half of all men over 50 have enlargement of the prostate gland.
Only one in 10 men with prostate symptoms will have cancer; in the rest, the cause of symptoms is usually a non-cancerous enlargement known as benign prostatic hypertrophy. Benign enlargement of the prostate gland tends to occur at the same age as prostate cancer, but there is no evidence that one leads to another.
Prostate cancer is one of the most common causes of death from cancer in New Zealand men. Every year about 2000 to 3000 cases of prostate cancer are diagnosed, three quarters in men over 70. About 500 men die from the disease every year, nearly half of them over 80 years old.
The figures are not as worrying as they seem. More men who have been diagnosed as having prostate cancer die from other causes than die from the cancer itself. However, it is difficult, even with screening, to identify tumours that are going to develop rapidly.
What screening tests for prostate cancer are available?
The term screening refers to tests that pick up disease at an early stage. The most common test for prostate cancer is the PSA test, which measures a substance called Prostate Specific Antigen (PSA) in the blood.
PSA is a normal product of the prostate gland, but raised levels suggest cancer or other prostate problems. Doctors looking for prostate cancer will do a PSA test in conjunction with a rectal examination of the prostate gland itself.
If the PSA test is positive, other tests and investigations will have to be done before a definite diagnosis of cancer can be made. This usually requires an ultrasound test and a needle biopsy of the prostate gland.
Three quarters of men who have a positive PSA test will not have cancer, so the PSA test is not itself a reliable diagnosis. There is also a small risk of infection and bleeding from a biopsy, so the test is only done if there is a suspicion that a cancer is present.
How is prostate cancer treated?
The main ways to treat prostate cancer that has not spread are either radical surgery to remove the whole prostate gland (radical prostatectomy) or radiotherapy.
Because both forms of treatment carry significant risk of complications like impotence, incontinence and bowel problems, 'watchful waiting' can be considered as an alternative option.
The current evidence is that treating some prostate cancers does not improve your likelihood of survival, and may reduce the quality of your remaining life.