Prostate
The
prostate is an
exocrine gland of the male
mammalian
reproductive system. Its main function is to store and secrete a clear, slightly
basic fluid that constitutes up to one-third of the volume of
semen. The prostate differs considerably between species
anatomically,
chemically, and
physiologically. 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.
Skene's glands found in many females are
homologous to the prostate gland in males.
The
male urethra has two functions: to carry urine from the bladder during
urination and to carry semen during
ejaculation. Within the prostate, the urethra coming from the bladder is called the
prostatic urethra and merges with the two
ejaculatory ducts. Semen is composed of
sperm and
seminal fluid; about 10-30% of the seminal fluid is produced by the prostate gland, the rest is produced by the two
seminal vesicles. The prostate also contains some
smooth muscle that helps to expel semen during
ejaculation.
Prostatic secretions vary between species. They are generally composed of simple sugars, and are often slightly
basic. In human prostatic secretions, the protein content is less than 1% and includes
proteolytic enzymes,
acid phosphatase, and
prostate-specific antigen. The secretions also contain
zinc and
citric acid.
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.
The prostate gland represents the modified wall of the proximal portion of the male urethra and develops by the 9th week of embryonic life. Condensation of mesenchyme, urethra and Woolfian ducts gives rise to the adult prostate gland, a composite organ made up of several glandular and non-glandular components tightly fused within the a common capsule. The prostate gland has four distinct glandular regions, two of which arise from different segments of the prostatic urethra:# The Peripheral Zone (PZ) - The sub-capsular portion of the posterior aspect of the prostate gland which surrounds the distal urethra and comprises up to 70% of the normal prostate gland in young men. It is from this portion of the gland that more than 70% of prostatic cancers originate.# The Central Zone (CZ) - This zone constitutes approximately 25% of the normal prostate gland and surrounds the ejaculatory ducts. Central zone tumours account for more than 25% of all prostate cancers. # The Transition Zone (TZ) - This zone is responsible for 5% of the prostate volume and very rarely is associated with carcinoma. The transition zone surrounds the proximal urethra and is the region of the prostate gland which grows throughout life and is responsible for the disease of benign prostatic enlargement.# The Anterior Fibro-muscular zone - This zone accounts for approximately 5% of the prostatic weight, is usually devoid of glandular components, and composed only, as its name suggests, of muscle and fibrous tissue.
Older men often have
corpora amylacea, dense accumulations of calcified proteinaceous material, in the ducts of their prostates. The corpora amylacea may obstruct the lumens of the prostatic ducts, and may underlie some cases of
benign prostatic hyperplasia.
|
Prostate under a microscope This image shows the microscopic glands of the prostate |
Inflammation of the prostate gland is known as
prostatitis. If the prostate grows too large it may constrict the urethra and impede the flow of urine, making
urination difficult and painful and in extreme cases completely impossible. Prostatitis is treated with
antibiotics,
prostate massage or
surgery.
In older men, the prostate often enlarges to the point where urination becomes difficult. This is known as
benign prostatic hyperplasia and can be treated with medication or with surgery that removes part of the prostate. The surgery most often used in such cases is called transurethral resection of the prostate (TURP or TUR). In TURP, an instrument is inserted through the urethra to remove prostate tissue that is pressing against the upper part of the urethra and restricting the flow of urine.
Prostate cancer is one of the most common
cancers affecting elderly men in
developed countries and a major cause of
death. Regular
rectal exams are recommended for older men to detect prostate cancer early. There is also a
blood test that measures the concentration of a
protein, Prostate Specific Antigen (PSA), which is normally very low. Elevated test results, or a rapid rise in the test reading from one test to the next, may be an indicator of disorder within the prostate--either prostatitis, benign hyperplasia or prostate cancer. The PSA test cannot distinguish among them, but can lead a doctor to investigate further. Prostate cancer is treated with hormone manipulation (prevention of production of testosterone),
radiation and/or surgery. It has recently been found that the drug
Docetaxel can be effective in the treatment of prostate cancer.
Epidemiological evidence has shown higher rates of prostate cancer in men who are infected with the human papilloma virus. There is other evidence that men who frequent prostitutes also have higher rates of prostate cancer. Priests who are celibate have lower rates of prostate cancer.
The prostate produces powerful immunosuppresive compounds that enhance fertilization when a female is inseminated but those same proteins, polamines and prostaglandins can promote the growth of prostate cancer and infections by preventing an effective intraprostatic immune response.
Bacteria that are trapped in biofilm within the prostate ducts are extremely difficult to eradicate. This chronic prostatic inflammation is associated with the development of prostate cancer.
Stimulation of the prostate gland in males has been compared to stimulation of the
Grafenberg spot in females in that prostate stimulation can result in a more powerful
orgasm. See
Prostate massage for more information.
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Bulbourethral glands
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Cowper's glands
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Cystoscopy*
Prostate milking*
Prostatectomy*
Seminal vesicles
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Urinary retention
