Prostate

Anatomy

The prostate is a six-sided organ consisting of glandular and fibromuscular tissue. It resides in the pelvic cavity and typically measures 4 x 3 x 2 cm and weighs around 20 grams. The prostate is encapsulated by both a true internal connective tissue capsule and a false external capsule, which extends from the pelvic fascia.

Parts and relations

The base of the prostate is adjacent to the neck of the urinary bladder and surrounds the prostatic urethra, which exits at the apex.

The prostate is divided into four main zones:

• The peripheral zone, the outermost region of the prostate, envelops the central zone and includes the posterior and lateral areas. It contains about 70% of the glandular tissue and is the primary site of prostate cancer. Though it extends inferiorly, it does not reach the base of the prostate. Portions of the prostatic urethra outside this zone are covered by anterior myoelastic stroma and supported by striated and detrusor muscle fibers.
• The central zone is cone-shaped, with its base at the prostate's base and apex surrounding the ejaculatory ducts. It lies between the peripheral and transitional zones and accounts for about 25% of the glandular tissue.
• The transitional zone, surrounding the prostatic urethra, makes up roughly 5% of the glandular tissue and contains mucosal glands. Though small in young men, it commonly enlarges with age due to benign prostatic hyperplasia. It extends from the prostate's base to the seminal colliculus and is encircled by the central zone.
• The periurethral zone surrounds the prostatic urethra near the transitional zone and contains mucosal and submucosal glands.

Understanding the structural relations of the prostate is key to comprehending its functions and clinical implications.

• Base: The superior portion of the prostate, adjacent to the urinary bladder and internal urethral sphincter. The base is also connected to the seminal vesicles and retrovesical space.
• Apex: The inferior portion of the prostate, which is connected to the bulbourethral glands, external urethral sphincter, and the retroprostatic part of the rectovesical space.
• Anterior surface: Located near the retropubic space, bordered by the posterior part of the pubic symphysis.
• Posterior surface: Connected to the rectovesical fascia and distal rectum, which is important in digital rectal examinations for detecting abnormalities.
• Inferolateral surfaces: Adjacent to the levator ani muscles, which play a role in supporting the prostate and aiding in ejaculation.

Histology

The histological makeup of the prostate is essential to its function in reproduction.

The prostate is composed primarily of glandular tissue, supported by a fibromuscular stroma. The stroma contains smooth muscle fibers and elastic fibers that contribute to the organ’s ability to contract and secrete prostatic fluids.

Blood supply

The prostate receives arterial blood from three primary sources:

• Internal pudendal artery: Supplies blood to the lower portion of the prostate.
• Inferior vesical artery: Primarily supplies the bladder but also sends branches to the prostate (urethral branches and capsular branches).
• Middle rectal arteries: Supplies blood to the prostate, particularly its posterior regions.

These arteries arise from the internal iliac artery. The venous blood from the prostate drains into the prostatic venous plexus, which is located between the true and false capsules. This venous plexus then drains into the internal iliac vein and subsequently into the inferior vena cava.

Innervation

The prostate is richly innervated by both sympathetic and parasympathetic fibers, which play distinct roles in its functions:

• Sympathetic innervation: Arises from the superior hypogastric plexus and is crucial for smooth muscle contraction during ejaculation.

• Parasympathetic innervation: Originates from the pelvic splanchnic nerves and is responsible for stimulating glandular secretion and erectile function.

The nerve fibers from the inferior hypogastric plexus contribute to the smooth muscle contraction in the prostate, while the prostatic plexus regulates secretomotor function.

This complex innervation allows the prostate to play a vital role in both reproductive and urinary functions. Additionally, sensory fibers from the prostate provide feedback for reflexive actions related to ejaculation and prostate health.

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Lymphatic drainage

The lymphatic drainage of the prostate is complex, reflecting its anatomical relationships with surrounding structures. The lymph from the prostate drains through three primary pathways:

• Lateral pathway: Drains to the external iliac lymph nodes, which also drain the ductus deferens and seminal vesicles.
• Laterodorsal pathway: Drains into the internal iliac lymph nodes.
• Dorsal pathway: Drains into the sacral and common iliac lymph nodes.

This drainage system is clinically significant, especially in the context of prostate cancer. The prostate's close association with the bladder and rectum means that cancer can spread to adjacent lymph nodes, influencing the stage of the disease and treatment options.

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