The Anatomy of the Prostate

The prostate secretes fluid that protects and nourishes sperm

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In men, the prostate is an important gland located between the penis and bladder, sitting just to the front of the rectum. The urethra, which carries urine from the bladder out of the body, runs through the center of this walnut-sized organ. Primarily, this gland serves the function of secreting fluid that both nourishes sperm and keeps it safe. The prostate is involved in a number of health conditions, and it’s quite influential in the overall health picture. The most notable of these are benign prostatic hyperplasia (characterized by an enlargement of the gland), prostate cancer, as well as prostatitis (bacterial infection).

Anatomy

Structure & Location

Located within the lesser pelvis just beneath the bladder and to the front of the rectum, the prostate is surrounded by a fibrous layer called a capsule. It wraps around the proximal (more central) portion of the urethra, and the seminal vesicles run above and behind this gland. Its shape is cone-like, with a base surrounding the neck of the urinary bladder and an apex below the sphincter. Anatomically speaking, it consists of five distinct lobes:

  • Anterior lobe: This front portion, positioned right in front of the urethra, consists of fibromuscular—rather than glandular—tissue.
  • Median lobe: A cone-shaped portion of the prostate, the median lobe sits between the two ejaculatory ducts (which deliver sperm to the seminal vesicles) and the urethra.
  • Lateral lobes: These two lobes—the right and left lateral lobes—comprise the majority of the body of the prostate. Their rear (posterior) ends are continuous, and they’re separated by the prostatic urethra, which is the widest part of the urethra.
  • Posterior lobe: The rear-facing lobe of the prostate is connected to the lateral lobes and is most frequently subject to medical examination.

This gland is also considered to be divided into several different zones, including: 

  • Central zone: This portion of the prostate surrounds the ejaculatory ducts and comprises 25% of its mass.
  • Peripheral zone: Making up 70% of this organ, this zone surrounds a majority of the central zone, while also wrapping around a portion of the prostatic urethra.
  • Transition zone: This smaller portion—representing 5% encircles the part of the urethra between the urinary bladder and verumontanum, a structure towards the floor of the urethra.

As indicated above, several tubular structures pass through the prostate, including the proximal urethra and two ejaculatory ducts. The latter of these accesses the prostate at the point where it emerges from the seminal vesicles, and both structures converge at a portion of the urethra within the prostate called the “seminal colliculus.”

Anatomical Variations

Occasionally, doctors find congenital variations in the anatomy of the prostate, meaning the gland develops irregular features. Though relatively uncommon, absence of the median lobe of this gland has been reported, meaning anterior and lateral lobes are directly connected. In addition, some individuals are born with an extra lobe to this gland.

Function

The prostate is an important supportive organ of the male reproductive system, serving an essential function in the health and maintenance of sperm (male sex cells). The primary role of this gland is to secrete an alkaline solution that surrounds and protects male sperm in the acidic environment of the female vagina. Basically, fluid from the prostate—including the enzyme prostate-specific antigen (PSA)—neutralizes the area immediately surrounding sperm that have accessed this part of the anatomy, allowing them a longer amount of time to access the egg. Furthermore, fluids from the prostate work to nourish and feed sperm.

These functions are essential for the process of conception, and PSA plays a particularly important role in male fertility, as it helps increase motility of sperm. Essentially, this fluid combines with sperm from the testicles as well as fluids from the seminal vesicles and bulbourethral gland (a small gland beneath the prostate) to make up male semen. This combination occurs in the urethra.   

Associated Conditions

Primarily, there are three major health conditions that affect the prostate. These are:

Benign Prostatic Hyperplasia (BPH)

One of the most common issues that arises with this gland—especially among seniors—this condition is characterized by excessive enlargement of the prostate. This condition can narrow the urethra, or lead to impingement of the bladder, leading to symptoms such as increased frequency of urination, nocturia (interruption of sleep due to a need to urinate), as well as weak stream. Treatment approaches tend to be more conservative. Alpha-1 receptor blocker drugs can help reduce smooth muscle tone in the urethra to improve passage of urine. Alternately, 5-alpha-reductase inhibitors may be prescribed to reduce hormone production in the prostate and shrink its size. 

Prostate Cancer

As with many types of cancer, current or former smokers, those with family history of cancer, people with a higher body mass index (BMI), and/or those who’ve been exposed to radiation are at increased risk of developing prostate cancer. Especially in initial presentation, this condition can mimic BPH; however, lower back pain can also occur, and there can be risk of further spreading. There are a wide range of treatment options for this condition, including prostatectomy (a minimally-invasive surgical removal of the gland performed either robotically or using laparoscopic methods), radiation therapy (using radio waves to tackle the cancerous tumors), or chemotherapy (the injection or ingestion of drugs that target and kill cancer cells).

Prostatitis

Bacterial infection of the prostate is called prostatitis, and this condition can lead to pain in the area. This disease can be difficult to diagnose, as the same kind of bacteria can also lead to urinary tract infection; however, antibiotic treatments are highly effective in taking on the issue.

Tests

The health and wellbeing of the prostate can be tested in a variety of ways, with procedures varying from physical examination to the use of imaging technologies. Here’s a quick breakdown of some of the most common approaches:

Digital Rectal Examination (DRE)

The first-line approach to prostate health assessment is the digital rectal examination. Wearing gloves and lubricating his hand, the doctor will ask the patient to lay over an examination table. They will then insert a finger into the rectum to feel the prostate, checking for inflammation or any other irregularities in shape. Though uncomfortable, the procedure is brief, and it’s a routine part of health examination for men aged 50 and up.

Prostate-Specific Antigen (PSA) Test

This is a test that assesses levels of PSA within the bloodstream. It’s recommended for men over 50, or those who may have other risk factors for prostate cancer. Basically, abnormally high levels of PSA in the blood can be a sign of cancer, and positive results tend to warrant further investigation.

Urinalysis

Analysis of the urine may be needed to diagnose prostatitis or the presence of abnormal substances in the prostate. This test can also help isolate urethral versus prostate infection. In addition, overall function of the prostate, urethra, and bladder can be assessed using urodynamic testing, which looks at flow of urine as well as storage capacity.

Abdominal Ultrasound

Ultrasound involves the use of benign soundwaves to map structures in the abdomen, including the prostate. Basically, a gel is applied to the abdomen and a hand-held device called a transducer is moved over the area. Images captured this way are examined by specialists to get an overall sense of the health of this organ.

Prostate Biopsy

When previous tests have unearthed potential cancer, biopsy guided by ultrasound may be called for to confirm the diagnosis. Basically, using this imaging approach, a needle is guided to the prostate to collect a tissue sample. This sample can then be assessed for the presence of cancer cells. 

Imaging Scans

Imaging techniques are also part of the diagnostic arsenal of the doctor and may be required to diagnose prostate issues. Magnetic resonance imaging (MRI) can collect images of internal organs using radio waves and magnets. Computed tomography (CT) scans combine X-ray and digital imaging software to create three-dimensional images of structures in and around the prostate and urethra. These approaches can help detect abnormal growths, though biopsy is often needed to confirm cancer.

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