. The prostate gland is a male accessory sex organ comprised of 30-50 branched glands, weighs about 20 grams and measures 4 x 2 x 3 centimeters (about the size of a walnut). It is surrounded by a fibroelastic capsule that penetrates the gland to divide it into lobes. The capsule and the stroma within the gland contain smooth muscle cells capable of contracting to expell the prostatic fluid. The prostate lies in front of the rectum just under the bladder and surrounds a portion of the urethra. Ejaculatory ducts join the urethra within the prostate gland. The prostate produces an alkaline fluid rich in citric acid, spermine, cholesterol, phosphlipids, fibrinogenase, fibrinolysin, zinc and acid phosphatase, and other proteins. It contributes about 30% of the total seminal fluid volume.