General structural plan of the organ
Histologically, the prostate is classified as a fibromuscular and glandular organ. Its structure is formed by a combination of glandular parenchyma and a robust fibromuscular stroma.
The stromal component has a radial architectonics—connective tissue and muscular elements diverge from the center of the organ (from the urethra) toward the periphery. Large stromal septa divide the organ into lobules, while finer layers penetrate inside these lobules, surrounding individual glands. The stroma consists of loose fibrous connective tissue rich in elastic fibers, and bundles of smooth myocytes. In a histological section, the combination of branching terminal parts and radially diverging stroma creates a visual pattern resembling an exotic plant leaf.
The muscular elements of the stroma form two layers (circular and longitudinal) around the lobules and terminal parts. A sheath consisting of an inner longitudinal and an outer circular layer is also formed around the urethra passing through the organ.
Glandular apparatus: parenchyma and classification
The glandular parenchyma consists of 30–50 mucous tubuloalveolar glands characterized by highly branched terminal parts. The excretory ducts of the glands merge into larger ones and open into the prostatic urethra. In humans, the excretory duct system has a wide lumen (in contrast to dogs, for example, which have narrow ducts).
Depending on their localization, the glands are divided into three groups:
- Group I: Glands located directly within the mucosal lining of the urethra.
- Group II: Submucosal glands located in the connective tissue surrounding the urethra.
- Group III: Main prostate glands, occupying the primary, peripheral part of the organ.
Cellular composition of the terminal parts and urethra
Three cell types are distinguished in the epithelium of the tubuloalveolar glands:
- Principal cells (exocrinocytes): Cuboidal or columnar in shape. These are mucous cells that produce the main components of the secretion.
- Basal cells: Small elements resembling intercalated cells. They act as stem (cambial) cells for epithelial regeneration.
- Endocrine cells: Rarely encountered, they secrete hormones with a paracrine (local) effect.
As the excretory ducts increase in size, their single-layered lining is replaced by pseudostratified epithelium.
The prostatic urethra passes through the anterior part of the prostate. It has a narrow stellate lumen and is lined with transitional epithelium, characteristic of the urinary tract. Beneath the epithelium lie the lamina propria of the mucosa, the submucosa, and the smooth muscle layer.
Functions of the prostate gland
The prostate gland performs three key functions: exocrine, endocrine, and contractile.
The exocrine function consists of producing a secretion that contributes to the fluid part of the semen. The main components of the secretion are:
- Proteolytic enzymes (e.g., fibrinolysin): ensure the liquefaction of semen.
- Phospholipids and annexins (carrier proteins): replace cholesterol in sperm membranes with phospholipids, increasing their lability in preparation for fertilization.
- Prostasomes: small membrane vesicles that bind to spermatozoa and protect them from immune attack in the female reproductive tract.
- Prostaglandins: stimulate contractions of the smooth musculature of the female tract to propel sperm (historically, this group of substances was named precisely because they were first discovered in prostatic secretion).
The endocrine function includes the synthesis of factors released into the bloodstream (e.g., a follicle-stimulating hormone analogue that stimulates testicular activity, and a hypothalamic sex differentiation factor). In addition, an APUD-like system of local hormones operates within the gland. Endocrine cells release serotonin, calcitonin, somatostatin, and cholecystokinin into the intercellular space (paracrine effect). Serotonin and cholecystokinin regulate myocyte contraction, while somatostatin controls glandular secretion.
The contractile function is carried out by the robust stroma. During ejaculation, the muscular elements contract, ensuring the active expulsion of secretion from the glands. Simultaneously, an involuntary urethral sphincter is formed, preventing the retrograde flow of seminal fluid into the urinary bladder.
Age-related changes
After 50–60 years of age, age-related tissue remodeling begins in the prostate gland. Atrophy of the glandular component (parenchyma) is observed, accompanied by the proliferation of stromal connective tissue.
A characteristic sign of organ aging is the formation of prostatic concretions (stones). These are laminated bodies located in the lumen of the terminal parts of the glands and excretory ducts. These concretions consist of remnants of destroyed epithelium, components of thick secretion, and mineral substances, predominantly calcium phosphate.
Briefly: answers to topical questions
Which arteries supply blood to the prostate gland?
Blood supply to the prostate is provided by branches of the internal iliac artery (a. iliaca interna). The main vascular trunks feeding the organ are:
- Inferior vesical arteries (aa. vesicales inferiores) — directed toward the bladder neck, prostate, and seminal vesicles.
- Middle rectal arteries (aa. rectales mediae) — also give off vascular branches to the glandular tissue.
Where does lymphatic drainage from the prostate gland occur?
Lymphatic drainage from the prostate goes to regional lymph nodes located in the pelvic cavity. Lymph collects in the following groups of nodes:
- Internal iliac nodes — lie along the course of the internal iliac artery (a. iliaca interna).
- External iliac nodes — localized along the course of the external iliac artery (a. iliaca externa).
- Sacral nodes — located directly on the pelvic surface of the sacrum.
What is the innervation of the prostate gland?
The prostate receives autonomic innervation via the hypogastric / inferior hypogastric (pelvic) plexuses.
- Sympathetic innervation: efferent sympathetic fibers from the upper lumbar segments of the spinal cord pass through the periarterial nerve plexus / hypogastric plexus to the seminal vesicles, prostate gland, and ductus deferens.
- Functional significance: stimulation of the hypogastric plexus triggers ejaculation.
- Inferior hypogastric plexuses: formed from branches of the superior hypogastric plexus; pelvic splanchnic nerves join them, and the nerve plexuses of the pelvic organs are formed from the branches of these plexuses.
To remember the composition of prostatic secretion, use the acronym FFPP: Enzymes (proteolytic), Phospholipids, Prostasomes, Prostaglandins.
Class and exam questions
Why is the prostate gland called a fibromuscular organ?
It consists of glandular parenchyma (30–50 mucous glands) and a robust fibromuscular stroma necessary for expelling secretion during ejaculation.
What are prostasomes and what are they for?
Prostasomes are small membrane vesicles in the prostatic secretion. They attach to spermatozoa, protecting them from the immune system in the female reproductive tract.
What hormones does the APUD-like system of the prostate produce?
Prostate cells release serotonin, calcitonin, somatostatin, and cholecystokinin via paracrine signaling for the local regulation of myocyte contraction and secretion.
What are prostatic calculi (concretions)?
These are laminated structures composed of epithelial debris, secretion, and calcium phosphate that accumulate in the lumen of glands and ducts during age-related changes (after 50–60 years).
What else to study on this topic
- Morphology and cell types of tubuloalveolar glands
- Mechanism of action of secretional phospholipids on sperm membranes
- Histological structure of the prostatic urethra
- Architectonics of the smooth muscle stroma of the prostate gland
- Paracrine regulation: effects of serotonin and somatostatin
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