The prostate gland, which is normally about the size and shape of a walnut, wraps around the urethra between the pubic bone and the rectum, below the bladder. In the early stage of prostate enlargement, the bladder muscle becomes thicker and forces urine through the narrowed urethra by contracting more powerfully. As a result, the bladder muscle may become more sensitive, causing a need to urinate more often and more suddenly. The prostate grows larger due to an increase in the number of cells (hyperplasia). However, the precise reason for this increase is unknown. A variety of factors may be involved, including androgens (male hormones), estrogens, growth factors and other cell signaling pathways.

ENLARGED PROSTATE SYMPTOMS AND CAUSES

In men, urine flows from the bladder through the urethra. BPH is a benign (noncancerous) enlargement of the prostate that blocks the flow of urine through the urethra. The prostate cells gradually multiply, creating an enlargement that puts pressure on the urethra - the "chute" through which urine and semen exit the body.

As the urethra narrows, the bladder has to contract more forcefully to push urine through the body.

Over time, the bladder muscle may gradually become stronger, thicker, and overly sensitive; it begins to contract even when it contains small amounts of urine, causing a need to urinate frequently. Eventually, the bladder muscle cannot overcome the effect of the narrowed urethra so urine remains in the bladder and it is not completely emptied.