The prostate is a gland that also works as a muscular switch
Walnut-sized and weighing about 11 grams, the prostate does two jobs. It makes a slightly alkaline fluid that helps sperm survive, and its internal muscles flip the urethra between passing urine and ejaculation. Greek gave it its name: a guardian, one who stands in front.
Every male mammal has a prostate, though its anatomy and chemistry vary between species. In men it sits in the pelvis just beneath the bladder, wrapped around the stretch of urethra that meets the two ejaculatory ducts, and enclosed in an elastic, fibromuscular capsule. Typical weights run from 7 to 16 grams. Oddly, the Greek term prostátēs was first applied to the seminal vesicles rather than to this gland.
The switching mechanism relies on two muscle systems running lengthwise beside the urethra. One along the front widens the channel for urination; one along the back sets it into the ejaculatory position. Smooth muscle also squeezes prostatic fluid into the first portion of ejaculate along with most of the sperm. Those sperm fare better than the few carried mainly in seminal vesicle fluid, showing stronger swimming, longer survival and better-protected DNA. The fluid's alkalinity offsets the acidity of the vagina.
Anatomists describe the interior in two ways. Older accounts divide it into five lobes, visible in dissection, while modern imaging and microscopy favour three or four zones, which are more consistent. The glandular tissue drains through 12 to 20 main ducts into the urethra, set in fibrous tissue and smooth muscle continuous with the bladder wall. With age, thickened deposits called corpora amylacea accumulate inside.
Genetically it is busy: almost 75 percent of the roughly 20,000 protein-coding human genes are active in a normal prostate, and about 20 are highly specific to it, including those for prostate specific antigen, or PSA. In the embryo it starts to form late in the third month, as buds sprout from the developing urethra. It depends on male hormones, chiefly dihydrotestosterone derived from testosterone, and keeps growing until about the fourth decade. Its disorders include enlargement, inflammation, infection and cancer.
Source: Prostate
