Prostate

Where is the prostate?

It is shaped like an upside-down cone. Its base, at the top, surrounds the neck of the bladder, and its apex, at the bottom, rests on the external urethral sphincter. (StatPearls, Abdomen and Pelvis, Prostate)

It sits just below the bladder and in front of the rectum. OpenStax compares its size to a walnut, and Gray’s 1918 text to a chestnut. (OpenStax A&P 2e, 27.1; StatPearls, Abdomen and Pelvis, Prostate; Gray 1918, 3c. 6. The Prostate)

What are the zones and lobes of the prostate?

By its tissue it has three zones. The central zone forms the base around the ejaculatory ducts, the peripheral zone is about 70% of the gland, and the small transition zone surrounds the urethra between the bladder and the seminal colliculus (verumontanum). (StatPearls, Abdomen and Pelvis, Prostate)

An anterior fibromuscular stroma, with no glands, lies at the front, and a fibrous capsule encloses the whole gland. (StatPearls, Abdomen and Pelvis, Prostate)

Many anatomy texts describe five lobes: anterior, posterior, two lateral and a median lobe. In the clinic it is usually described as two lateral lobes and a median lobe. (StatPearls, Abdomen and Pelvis, Prostate)

Two ejaculatory ducts enter it from the seminal vesicles, run downward and inward, and open into the urethra inside the gland at the seminal colliculus. (StatPearls, Abdomen and Pelvis, Prostate)

What does the prostate do?

It adds an alkaline fluid to semen that offsets the acidity of the vagina, so sperm live longer, along with proteins and enzymes that nourish them. The fructose that fuels sperm comes from the seminal vesicles. (OpenStax A&P 2e, 27.1; StatPearls, Abdomen and Pelvis, Prostate and Physiology, Male Reproductive System)

It keeps growing as men age, by about 2% to 2.5% in volume a year, and half of men over 50 show benign prostatic hyperplasia. (OpenStax A&P 2e, 27.1; StatPearls, Benign Prostatic Hyperplasia)

What lies next to the prostate?

In front, retropubic fat and the prostatic venous plexus separate it from the pubic symphysis. Behind, the rectovesical septum (Denonvilliers fascia) separates it from the rectum, and at its sides lies the levator ani of the pelvic floor. (StatPearls, Abdomen and Pelvis, Prostate)

Below it, the external urethral sphincter wraps around the urethra and helps control urinary and ejaculatory flow. (StatPearls, Abdomen and Pelvis, Prostate)

Its main artery is the inferior vesical artery, with help from the middle rectal and internal pudendal arteries. Its veins form the prostatic plexus, which drains to the internal iliac veins. (StatPearls, Abdomen and Pelvis, Prostate)

Its nerves come from the inferior hypogastric plexus: sympathetic fibers through the hypogastric nerve and parasympathetic fibers through the pelvic nerve. (StatPearls, Abdomen and Pelvis, Prostate)

Where the sources differ

OpenStax says prostatic fluid first thickens semen and then thins it. StatPearls says the gel forms from semenogelin made by the seminal vesicles, and prostate-specific antigen then liquefies it. (OpenStax A&P 2e, 27.1; StatPearls, Abdomen and Pelvis, Seminal Vesicle)