Anatomy of the Prostate Gland

The prostate is a small gland (about the size of a walnut when it has not been enlarged in size by disease) that wraps around the urethra, the tube that carries urine from the bladder to outside the body. The nerves vital to erections go around the lateral edge of the prostate. The prostate is also connected to the ejaculatory ducts and contributes to parts of the semen. 

While it is small, different areas of the prostate have different functions. Most surgeons attempt to remove only the necessary tissue when performing ​prostate surgery (for benign enlargement, or outflow obstruction) or a biopsy in order to preserve as much function as possible. For known prostate cancer, surgical intervention includes removal of the entire gland of the prostate (called a radical prostatectomy).

When describing the prostate’s anatomy, it is divided into both zones and lobes. Your surgeon may refer to a specific zone, a specific lobe, or both when describing your surgery or diagnosis.

Zones of the Prostate

The prostate anatomy can be divided into zones, which are categorized by the function of the prostate tissue. The prostate is made up of the peripheral, central, and transitional zones.

The peripheral zone is the outermost area of the prostate, resting closest to the wall of the rectum. It makes up approximately 70% of a healthy prostate gland.

The next layer is the central zone, which is approximately 25% of the prostate tissue. This area contains the ejaculatory ducts, which help move semen through the urethra and out of the body.

The transitional zone of the prostate, resting next to the urethra, makes up around 5% of the prostate at puberty. This zone continues to increase in size throughout adulthood.

Your doctor may do a prostate ultrasound or get a prostate MRI to help characterize the zones of the prostate if needed for surgical planning.

Lobes of the Prostate

The prostate is made up of five lobes. Your doctor my do a procedure called cystoscopy to see if the lobes are blocking the inside of the urethra.:

• Anterior lobe: In front or the urethra. This tissue is non-glandular, meaning it does not secrete fluids. It is made up of muscle and fibrous tissue.
• Median lobe: Between the urethra and the ejaculatory ducts.
• Lateral lobes: These two lobes surround the urethra, and make up most of the mass of the prostate.
• Posterior lobe: Connected to the lateral lobes. This is the part of the prostate that your healthcare provider checks during a digital rectal exam.

The Size of the Prostate

A typical prostate is slightly larger than a walnut. Prostate medications, resections and radiation can make the prostate smaller than usual. Diseases such as benign prostatic hyperplasia or prostate cancer can make the prostate much larger than usual. Men commonly experience symptoms, such as difficulty urinating, weak flow, urgency when the prostate begins to enlarge.