What is the prostate gland? Definition

The prostate is a gland, like the thyroid gland or the adrenal gland. It is not an organ like the heart or the liver or the kidneys. It belongs to the male reproductive system and is present exclusively, therefore, in the male population.

The prostate lies located just below the bladder and in front of the rectum and surrounds the upper part of the urethra. The urethra is a tube that empties urine from the urinary bladder. The urethra runs through the center of the prostate, from the bladder to the penis.

Anatomy

The prostate gland is about the size of a walnut with a conical shape. It has a superior base, an inferior apex, an anterior, a posterior, and two lateral surfaces.

The base faces upward towards the inferior surface of the bladder. The greater part of the base is in direct contact with the bladder wall.

The apex of the prostate gland consists of the distal part of the prostatic urethra covered by the anterior fibromuscular stroma, which consists of muscle fibers and connective tissue of the superior fascia of the urogenital diaphragm.

Functions

The prostate may not be essential for life but is certainly vital and absolutely necessary for reproduction. It performs three main functions:

1. Produces semen

The main function of the prostate is to produce fluid that together with the sperm cells produced by the testes and fluid from other glands, comprise the semen.

The vasa deferentia, also called ductus deferens, are muscular ducts that transport sperm from the epididymis of the testes to the seminal vesicles. The seminal vesicles also contribute fluid to semen during ejaculation.

The prostatic fluid contributes between 20–30% of the fluid of the total semen volume. The remaining portion of the semen is contributed by the seminal vesicles (50–65%) and the testicles (5%).

The prostatic fluid contains enzymes, zinc, and citric acid. It also contains an enzyme called the prostate-specific antigen (PSA), which maintains the thin viscosity and fluidity of the seminal fluid.

These components are responsible for making the semen an ideal medium for sperms to live in their journey through the urethra to the egg in the fallopian tube of the female reproductive system.

Though the prostatic fluid is acidic, the other components make the semen overall alkaline to counter the acidity of the vagina and protect the sperm from damage.

2. Helps in ejaculation

The forceful ejaculation of the semen outward through the urethra is brought about by the contraction of the muscles of the prostate.

During its contraction, the prostate closes the sphincter between the urinary bladder and the urethra. This prevents the ejaculate from entering the bladder as it passes into the urethra.

3. Hormone production

The prostate produces an enzyme called 5-alpha-reductase, which converts testosterone into its biologically active form called dihydrotestosterone (DHT).

DHT is necessary for the normal development and function of the prostate. It is also vital for the development of secondary sex characteristics, such as the growth of chest and facial hair.

Structure

The prostate is elastic to touch due to a capsule of connective tissue that surrounds it. It is categorized into four zones, which envelope the urethra in layers.

The zones are classified according to the type of prostate tissue.

  • The anterior fibromuscular zone is made of muscle and fibrous tissues.
  • The peripheral zone is made up of glandular tissue and is situated towards the posterior aspect of the prostate close to the rectal wall. When the doctor performs the digital rectal exam, it is this surface of the prostate he feels. About 70-80% of prostate cancers originate in the peripheral zone.
  • The central zone is the portion that surrounds the ejaculatory duct and makes up 25 percent of the prostate mass. About 5 percent of prostate cancers begin in this zone, which are very aggressive and likely to spread to the seminal vesicles.
  • The transition zone is the part of the prostate that surrounds the urethra as it enters the prostate and is the only part, which continues to grow throughout life. This zone gets bigger with age. This enlarged zone is what is commonly referred to as benign prostatic hyperplasia (BPH).

You need multiparametric magnetic resonance imaging (mpMRI) and not an ordinary ultrasound, to clearly see the four zones of the gland, and to differentiate between the healthy and diseased tissue such as cancer and its spread, if any, beyond the prostate capsule.

Common medical conditions of the prostate gland

1. Prostatitis

Prostatitis is inflammation of the prostate gland most commonly seen in men less than 50 years of age. It can be acute or chronic.

Acute prostatitis occurs due to bacterial infection and comes on suddenly. It clears up by treatment with antibiotics.

When the prostate inflammation lasts for more than three months, it attains a chronic form. It is called chronic prostatitis or chronic pelvic pain syndrome.

Symptoms include pain in the groin, difficulty in passing urine, painful urination and ejaculation, and fever.

2. Enlarged prostate

A non-malignant enlargement of the prostate is very common affecting virtually all men over 50 years. It presses and pinches the urethra, narrowing its lumen.

Its main symptom, therefore, is increased frequency and difficulty in urination, which tends to increase with age. This is called prostatomegaly or benign prostatic hyperplasia (BPH).

Medicines and sometimes surgery are the options to treat this condition.

As the condition persists, the bladder muscles weaken and the symptoms worsen. In severe cases, BPH can block and prevent urination completely. This is called urinary retention and requires immediate medical intervention.

Medicines used to treat BHP include Alpha-blockers and 5-alpha-reductase inhibitors. Alpha-blockers relax the muscles around the urethra to help urine flow and 5-alpha-reductase inhibitors reduce the level of DHT, which shrinks the prostate and improves urine flow.

Minimally invasive procedures include transurethral needle ablation of the prostate and transurethral microwave thermotherapy. Surgery (transurethral resection of the prostate) may be required in severe enlargement.

3. Prostate cancer

Prostate cancer is the most common type of cancer in men. It is the second leading cause of death due to cancer among men in the United States.

the patient may be asymptomatic initially. When symptoms do occur, they include increased urinary frequency, urgency, taking time to start urination, and other symptoms of BPH.

High PSA values usually indicate malignancy though this not always the case. If the biopsy confirms malignancy, a bone scan is done to rule out metastases in other parts of the body.

Surgery called prostatectomy is done in cases where the cancer is limited to the prostate. Radiation, hormone therapy, and chemotherapy are the other treatment options used in its cure.

Tests for prostate conditions

Digital rectal examination (DRE). The doctor inserts a lubricated gloved finger inside the rectum by which he can detect an enlarged prostate, lumps, or nodules caused by cancer, or tenderness caused by prostatitis.

Prostate–specific antigen (PSA). HIGH levels of the protein PSA mostly indicate prostate cancer. However, they may sometimes also increase in BHP

Transrectal ultrasound.  An ultrasound probe is inserted into the rectum close to the prostate. It provides images at different angles to help gauge the size of the prostate and see any abnormal growths.

Prostate biopsy.  A prostate biopsy is done if results from the initial tests mentioned above suggest that you may have cancer.  The urologist inserts a needle into the prostate through the rectum to remove samples of suspicious tissue under ultrasound guidance. These samples are then examined under the microscope for cell abnormalities that indicate may prostate cancer.

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