Prostate

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The prostate is a small gland, about the size of a walnut that sits at the base of the bladder.  It weighs about an ounce (25-30g).  It actually looks a little bit like an upside down, flattened cone.  The wider portion called the base actually points upwards while the tapered portion that points downwards is called the apex.  The urethra exits the bladder and enters the base of the prostate where it passes through the prostate and exits at the apex before continuing then on out through the penis. 

One of the roles of the prostate is to create prostatic fluid.  Prostatic fluid is a thick, semi-clear to light yellow fluid, not white.  It is released (squeezed) through the prostatic ducts in the urethra of the prostate.  Prostate fluid contains enzymes that help thin out semen after ejaculation, thus making it easier for sperm to swim.  Prostate fluid can sometimes be seen after a man has a bowel movement (the stool may press the prostate through the rectum enough to press prostate fluid through the prostatitc ducts and into the urethra).  Some men mistake this as a few drops of urine but it is thick and sticky rather than thin and watery like urine. ​Image below copyrighted by DNA Illustrations and used by permission.

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The pudendal nerves innervate the prostate.  The pudendal nerve has branches that are involved in sexual stimulation from the posterior scrotal nerve as well as nerves in the penis.  This innervation by the pudendal nerve makes the prostate extremely sensitive sexually.  In fact, between emission and expulsion, most sexual sensations are felt in the prostate and sexual sensitivity in the prostate may be one of the main causes of wet dreams. 

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PROSTATE ZONES

The prostate is also made up of different zones – or layers from the inside to the out.   

  • The prostate is surrounded by layers of facia and smooth muscle called the prostatic capsule.  The prostatic capsule helps the prostate contract during the emission phase of ejaculation.  See a cut side view of the prostate below.  Images below copyrighted by DNA Illustrations and used by permission.

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  • The fibromuscular zone sits mostly towards the front of the prostate (although the prostatic capsule that surrounds the entire prostate is an extension of this zone).  As the name suggests, this zone is made up of fibers and smooth muscles.  These muscles contract during ejaculation.  This is the only zone that doesn’t surround the ejaculatory duct which helps prevent the ejaculatory duct from being pinched off during ejaculation as well as preventing semeninal fluid from being forced back into the seminal vesicles and ampulla.  See the cut side view of the prostate below.

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  • The peripheral zone accounts for about 70% of the prostate volume.  Most of the gland cells that make prostate fluid are located here so this area is largely responsible for making some of the components of semen.  See the cut front view of the prostate below.

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  • The central zone makes up about 20-25% of the volume of the prostate.  The central zone is located deep in the rear upper half of the prostate and surrounds the ejaculatory duct.  The ejaculatory duct connects the seminal vesicles and ampulla to the urethra.

 

  • The transitional zone is a small zone in the center of the prostate that surrounds the urethra in the upper half of the prostate and supports the periurethral zone.  This accounts for about 10% of the prostate volume in younger years, but as aging occurs, this area can increase in size and cause difficulties urinating (click HERE to learn more about BPH).

  • The periurethral zone lines the urethra.  There are varying structures in this zone. 

    • The first of these is a raised ridge along the rear side of the urethra called the verumontanum. 

      • The two openings of the ejaculatory ducts are on this ridge.  Sperm from the ampulla and seminal vesicle fluid enters the urethra through these openings during emission. 

      • In between the ejaculatory duct openings is a pouch called the prostatic utricle.  The prostatic utricle is left over from fetal development from the collapsed Mullerian ducts.  Since the Mullerian ducts form the vagina in women, this small indentation in the prostate is sometimes called the male vagina.  It’s thought that the utricle contracts during emission, thus helping the ejaculatory ducts to open more widely. 

  • Near the verumontanum are a large number of small prostatic ducts.  During emission, the prostate contracts thus pressing prostatic fluid through the prostatic ducts into the urethra to mix with fluid from the ejaculatory ducts to form semen.  See the cut side view of the prostate below.

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Images on this page from top to bottom include:

  1. CLIPAREA/Shutterstock.com

  2. copyrighted by DNA Illustrations and used by permission.

  3. Original design

  4. copyrighted by DNA Illustrations and used by permission.

  5. copyrighted by DNA Illustrations and used by permission.

  6. copyrighted by DNA Illustrations and used by permission.

  7. copyrighted by DNA Illustrations and used by permission.