The prostate gland consists of glandular and stromal elements. The stroma contains smooth muscle and connective tissue. BPH involves an increase of all elements of the gland, but with a relatively greater increase of prostatic stroma.
The prostate requires male hormones (testosterone and dihydrotestosterone) to grow. These hormones do not cause BPH, but are necessary for it to develop.
Ageing and male hormones are the only proven risk factors for developing BPH. Any man with a normal prostate and functioning testes will develop BPH if he lives long enough.
The testes produce 95% of testosterone found in the body. Testosterone is converted to dihydrotestosterone in the prostate gland. The prostate gland is much more sensitive to dihydrotestosterone than testosterone. An enzyme called 5-alpha reductase mediates this conversion of testosterone to its active form. 5-Alpha reductase is specific to the prostate gland (it is not found anywhere else in the body) and can be manipulated medically (see treatment section).
Dihydrotestosterone causes the formation of growth factors within the prostate gland, which in turn lead to an imbalance between cell growth and programmed cell death (apotosis).
The net effect of all this is a slow progressive enlargement of the prostate gland over time. While the majority of older men have clinically enlarged prostate glands, this per se does not necessarily lead to symptoms or complications.
BPH can cause symptoms due to its effect on the prostate itself, or due to its obstructive effect on the bladder outlet (see symptoms).
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