Prostate and other Male Reproductive Glands

The prostate is a gland in the male reproductive system. The gland surrounds the bladder neck and a portion of the urethra. The prostate is an exocrine gland that produces a weakly acidic secretion, which accounts for roughly 20% of the seminal fluid. The prostate consists of multiple lobes and is made up of glandular and fibromuscular tissue. The glandular tissue has ducts that empty into the prostatic portion of the urethra, and the fibromuscular tissue encircles the urethra.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

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Development

  • The prostate arises from epithelial buds that emerge from the embryonic urogenital sinus.
  • The buds elongate and split, becoming hollow, forming the ducts and acini.
  • Interfascicular fibroblasts and the smooth muscle of the prostate arise from the urogenital sinus mesenchyme.
  • The prostatic Müllerian mesenchyma further differentiates in response to stimulation with male androgen hormones Hormones Hormones are messenger molecules that are synthesized in one part of the body and move through the bloodstream to exert specific regulatory effects on another part of the body. Hormones play critical roles in coordinating cellular activities throughout the body in response to the constant changes in both the internal and external environments. Hormones: Overview, forming the prostate.

Gross Anatomy

Structure of the prostate

  • Lobular fibromuscular gland, covered in a fibrous capsule, surrounding the prostatic urethra from the bladder base to the external urethral sphincter, where the membranous portion of the urethra begins
  • Average dimensions: 3 cm long, 4 cm wide, and 2 cm in anteroposterior (AP) depth
  • Located in the lesser pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 "hip" bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis and lies immediately:
    • Inferior to the bladder
    • Posterior to the pubic symphysis
    • Anterior to the rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal
  • Consists of both muscular and glandular tissue:
    • The glandular part makes up approximately ⅔ of the prostate; the other ⅓ is fibromuscular.
    • Glandular tissue can be subdivided into 3 distinct zones, which produce secretions that make up approximately 20% of the seminal fluid.
      • Main prostatic glands: make up the peripheral ⅔ of the gland and empty into the distal urethra
      • Submucosal (outer periurethral) glands: empty into the urethral sinuses
      • Mucosal (inner periurethral) glands: empty directly into the urethra 
  • The prostate gland is divided anatomically into 5 lobes:
    • An anterior lobe (isthmus):
      • Located anterior to the urethra
      • Fibromuscular: the muscle fibers that are a superior continuation of the external urethral sphincter to the bladder neck
      • Contains little, if any, glandular tissue
    • A posterior lobe:
      • Posterior to urethra
      • Inferior to ejaculatory ducts
    • 2 lateral lobes: located on either side of the urethra 
    • 1 median lobe: cone-shaped portion of the gland situated between the 2 ejaculatory ducts and the urethra
  • The prostate consists of histologically different areas; on this basis, the gland is divided into 4 zones:
    • The central zone:
      • It forms the base of the gland.
      • Encircles the ejaculatory ducts
      • 25% of glandular tissue
    • The peripheral zone: 
      • Encircles most of the central zone and partially surrounds the distal part of the prostatic urethra
      • Most prostate cancers arise from the peripheral zone.
      • 70% of this zone is made up of glandular tissue.
    •  The transition zone:
      • Encircles the portion of the urethra between the urinary bladder and verumontanum
      • 5% of glandular tissue
    • The anterior fibromuscular stroma:
      • This area has no glandular tissue.
      • Consists of mostly muscular and fibrous tissue
  • The urethra enters the prostate near its anterior border and passes between its anterior and middle thirds.
  • The ejaculatory ducts pass through its posterior region to open into the prostatic urethra.

Accessory glandular structures

  • Seminal glands (vesicles):
    • Elongated structure, approximately 5 cm long
    • Lies between the fundus of the bladder and the rectum Rectum The rectum and anal canal are the most terminal parts of the lower GI tract/large intestine that form a functional unit and control defecation. Fecal continence is maintained by several important anatomic structures including rectal folds, anal valves, the sling-like puborectalis muscle, and internal and external anal sphincters. Rectum and Anal Canal
    • The duct of the seminal gland joins the ductus deferens to form the ejaculatory duct.
    • Secrete a thick alkaline fluid with fructose (an energy source for sperm)
  • Bulbourethral glands (Cowper’s glands):
    • Small lobulated structures located immediately posterior and lateral to the membranous urethra and superior to the perineal membrane
    • Contraction of muscle fibers leads to the expulsion of clear mucus from the glands during sexual arousal.
Sagittal cross-section of the prostate

Anatomy of the prostate:
Cross-section of the prostate demonstrating its relation to the prostatic urethra, urethral sphincter, seminal vesicles, and bulbourethral gland

Image by BioDigital, edited by Lecturio

Neurovasculature and Lymphatics

Arterial supply

Blood vessels supplying the prostate arise from the internal iliac artery and enter the gland from the posterolateral region.

  • The iliac artery gives rise to inferior vesical.
  • The inferior vesical gives rise to 2 branches:
    • Urethral branch
    • Capsular branch
Anatomy of the vascular supply of the prostate and bladder

Anatomy of the vascular supply of the prostate and bladder:
The arterial blood supply of the prostate and bladder originates from the internal iliac artery, which gives off the inferior vesicle artery. This in turn gives rise to the prostatic artery, which branches in urethral and capsular groups which feed those portions of the prostate.

Image by Lecturio.

Venous drainage

  • The veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins surrounding the prostate join to form the prostatic venous plexus around the sides and base, which drains into the internal iliac veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins.
  • The prostatic venous plexus is continuous superiorly with the vesical venous plexus.
  • The prostatic venous plexus communicates posteriorly with the internal vertebral venous plexus.

Lymphatic drainage

  • Internal iliac lymph nodes
  • Sacral lymph nodes

Innervation

  • The prostate is innervated by autonomic fibers arising from the inferior hypogastric plexus: 
    • Sympathetic innervation from the hypogastric nerve
    • Parasympathetic innervation via the pelvic splanchnic nerve
  • Sensory innervation is provided by the hypogastric and pelvic plexuses.
  • Urethral sphincter motor innervation is supplied by somatic pudendal nerve fibers.

Microstructure

The prostate consists of glandular tissue and fibromuscular tissue.

  • Glandular epithelium Glandular epithelium Glandular epithelia, composed of epithelial tissue, are specialized structures that play a role in the production and release of enzymes, hormones, sweat, oil, and mucus in organisms. The secretion and release of these substances are prompted by either external or internal stimuli. Glandular Epithelium is arranged in acini and ducts lined by:
    • Luminal cells:
      • Columnar, with pale eosinophilic cytoplasm and round nuclei 
      • Secrete into the lumen, contributing to seminal fluid production
      • Strongly positive for PSA immunohistochemistry
    • Basal cells:
      • Basement membrane adjacent
      • Ovoid nuclei and inconspicuous cytoplasm
      • The number of basal cells varies between glands in an individual prostate.
    • Neuroendocrine cells: positive for neuroendocrine markers such as chromogranin and synaptophysin
  • Prostate secretions (along with seminal vesicular secretions) form the bulk of the seminal fluid. Acidic secretions are composed of:
    • Proteolytic enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body's constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes
    • Acid phosphatase
    • PSA
    • Fibrinolysin
    • Zn
The glandular columnar epithelium of the prostate gland (histological)

The glandular columnar epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium of the prostate gland (histological):
Note, on this slide, the prostatic concretion; these concretions can have a clinical application if they build up and impinge on the urethra → difficulty urinating

Image by Lecturio.

Clinical Relevance

  • Benign prostatic hyperplasia Benign prostatic hyperplasia Benign prostatic hyperplasia (BPH) is a condition indicating an increase in the number of stromal and epithelial cells within the prostate gland (transition zone). Benign prostatic hyperplasia is common in men > 50 years of age and may greatly affect their quality of life. Benign Prostatic Hyperplasia (BPH): a common condition in older men (> 50) characterized by a firm enlargement of the lateral and middle lobes. The growth is not premalignant and presents low levels of clinical risk. The most important symptoms include increased frequency of urination and slowness or dribbling of the urinary stream. Benign prostatic hyperplasia Benign prostatic hyperplasia Benign prostatic hyperplasia (BPH) is a condition indicating an increase in the number of stromal and epithelial cells within the prostate gland (transition zone). Benign prostatic hyperplasia is common in men > 50 years of age and may greatly affect their quality of life. Benign Prostatic Hyperplasia is detected via both blood PSA test and digital rectal exam (DRE). Various treatment options are available, including surgical and supportive.
  • Prostate cancer Prostate cancer Prostate cancer is one of the most common cancers affecting men. In the United States, the lifetime risk of being diagnosed with prostate cancer is approximately 11%, and the lifetime risk of death is 2.5%. Prostate cancer is a slow-growing cancer that takes years, or even decades, to develop into advanced disease. Prostate Cancer: among the most common cancers in men worldwide. Prostate cancer Prostate cancer Prostate cancer is one of the most common cancers affecting men. In the United States, the lifetime risk of being diagnosed with prostate cancer is approximately 11%, and the lifetime risk of death is 2.5%. Prostate cancer is a slow-growing cancer that takes years, or even decades, to develop into advanced disease. Prostate Cancer may cause no signs or symptoms in its early stages. Uncommonly, the cancer may present with nonspecific urinary symptoms, hematuria, or hematospermia. Diagnosis is based on PSA testing and DRE. A variety of treatment options are available, including surgery, chemotherapy, and radiation. The overall 5-year survival rate is over 98%.
  • Prostatitis Prostatitis Prostatitis is inflammation or an irritative condition of the prostate that presents as different syndromes: acute bacterial, chronic bacterial, chronic prostatitis/chronic pelvic pain, and asymptomatic. Bacterial prostatitis is easier to identify clinically and the management (antibiotics) is better established. Prostatitis: a term that indicates inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the prostate, which can be due to infectious or noninfectious causes. Bacterial prostatitis is easier to identify clinically and its management is better established. The main diagnostic tools for prostatitis are clinical history and physical exam. Prostate massage by DRE is only recommended in patients with chronic prostatitis and not for acute bacterial prostatitis.

References

  1. Drake, RL, et al. (2020). Chapter 5: Pelvis and perineum. In Gray’s Anatomy for Students, 4th Edition. Pages 467–468. Churchill Livingstone/Elsevier.
  2. Moore, KL, Dalley, AF, & Agur, AMR. (2014). Chapter 3: Pelvis and perineum, pelvic viscera. In Clinically Oriented Anatomy (7th Ed.). Pages 377–382. Lippincott Williams & Wilkins, a Wolters Kluwer business.
  3. Ittmann M. (2018). Anatomy and histology of the human and murine prostate. Cold Spring Harbor Perspectives in Medicine. Retrieved Sep 9, 2021, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5932577/
  4. Singh, O. (2021). Anatomy, abdomen and pelvis, prostate. Statpearls. Retrieved Sep 9, 2021, from https://www.statpearls.com/ArticleLibrary/viewarticle/27831

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