Prostate gland

Structure

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.

The prostate is a six-sided amalgamation of glandular and fibromuscular tissue that resides in the pelvic cavity. The typical dimensions of a healthy prostate are 4 x 3 x 2 cm (its width being the greatest), while weighing about 20 grams.

Position and zones

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 three main zones.

• Peripheral zone: The outermost region, containing the majority of the glandular tissue, except for its anterior portion. The zone extends inferiorly but does not reach the prostate's base. The part of the prostatic urethra not within the peripheral zone is covered by anterior myoelastic stroma, supported by striated muscle fibers from the urethral sphincter and detrusor muscle fibers from the bladder.
• Transition zone: This zone surrounds the prostatic urethra and extends from the base to the verumontanum. It is encircled by the conical central zone and extends from the prostate's base to the verumontanum, also encompassing the ejaculatory ducts behind the preprostatic urethra.
• Central zone: This zone is located between the peripheral and transition zones, encircling the ejaculatory ducts. It plays a smaller role in prostate pathologies but is important for its anatomical position and connection to the prostatic urethra.

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.

Prostate glands and secretions

The prostate’s primary function is the secretion of seminal fluid, which constitutes about 27% of the total ejaculate. Prostatic fluid contains:

• Prostate-specific antigen (PSA): An enzyme that helps liquify semen after ejaculation.
• Prostatic acid phosphatase: An enzyme involved in sperm motility.
• Fibrinolysin: A substance that helps dissolve the semen clot after ejaculation.
• Citric acid and zinc: These substances help maintain the acidity of the seminal fluid and support sperm health

Prostatic glands have irregularly shaped lumens lined with simple columnar or pseudostratified epithelium. The epithelium is responsible for secreting the prostatic fluid, while the surrounding stroma provides support and helps regulate glandular activity.

The presence of the prostatic urethra is also a key histological feature of the prostate. It has a horseshoe appearance (courtesy of the verumontanum), and epithelial projections thanks to the highly folded transitional epithelial layer. Posterior to the concavity of the prostatic urethra, the ejaculatory ducts and the prostatic utricle (blind ended duct along the midline of the verumontanum) can also be appreciated within the stroma of the prostate.

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.
• Middle rectal arteries: Supplies blood to the prostate, particularly its posterior regions.

The middle rectal and inferior vesical arteries arise from a common branch of the internal iliac artery. While the middle rectal artery only gives a few unnamed branches to the prostate, the inferior vesical artery gives a main branch to the urinary bladder and one to the prostate. The branch to the prostate then subdivides into two groups of arteries; one group primarily supplies the urethra and deep parts (urethral branches) while another group supplies the capsule and peripheral parts (capsular branches). The pudendal artery travels in the pudendal canal to supply the prostate and other pelvic and reproductive structures.

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

• Parasympathetic innervation: Originates from the pelvic splanchnic nerves and is responsible for stimulating glandular secretion and erectile function.
• Sympathetic innervation: Arises from the superior hypogastric plexus and is crucial for smooth muscle contraction during ejaculation.

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.

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.

It's almost time to start revising what you've learned about the prostate. Don't forget the importance of active recall!

Structural relations

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.