The prostate is a small gland found only in men. It is the size of a walnut and lies below the bladder. It surrounds the first part of the tube (urethra) which carries urine from the bladder to the penis. The function of the prostate is to secrete a fluid, rich in nutrients and enzymes for sperm, that makes up part of the semen.
The prostate gland lies in front of the rectum, and its posterior surface can be felt during a rectal examination. The prostate produces a protein called PSA (prostate specific antigen) , which can be raised in patients who have an enlarged prostate gland (BPH), prostate cancer, urinary tract infection, or following recent surgery or instrumentation (eg: putting in a catheter) to the lower urinary tract.