Position in the male reproductive system
The organs of the male reproductive system are functionally classified into three main groups. Each of them performs a specific task in the reproduction process.
- Gonads and deferent ducts: This group includes the testes proper (testicles), their epididymides, and the vas deferens. This is the production unit and transport pathways.
- Accessory glands (exocrine): These include the seminal vesicles, prostate gland, and bulbourethral (Cowper's) glands. They secrete components of seminal fluid.
- Organ of copulation: The male penis.
The testes are located outside the abdominal cavity, within the scrotum, which is a necessary condition for the normal temperature regime of spermatogenesis.
System of tunics (Tunics)
The testis is surrounded by a robust protective framework that is histologically and anatomically divided into 9 layers (when considered strictly layer by layer from outside inward).
- Superficial layers (I–II): Skin and dartos tunic (tunica dartos). An important histological feature of this zone is the complete absence of adipose tissue in the subcutaneous layer and the presence of smooth myocytes.
- Fascial layers (III–V): Three distinct fasciae located superficial and deep to the muscle layer, forming fascial sheaths.
- Muscle layer (VI): The muscular tunic known as the cremaster muscle (m. cremaster). Unlike the dartos tunic, it is formed by skeletal muscle tissue and is responsible for mechanically elevating the organ.
- Serous tunic (VII–VIII): Tunica vaginalis (tunica vaginalis). This is a derivative of the peritoneum consisting of two layers: parietal and visceral, between which lies the serous cavity.
- Proper capsule (IX): Tunica albuginea (tunica albuginea), consisting of dense fibrous connective tissue.
Histological nuance: Only the two innermost layers are tightly fused to the testicular tissue itself — the visceral layer of the tunica vaginalis and the tunica albuginea.
Internal architectonics and stroma
The internal connective tissue framework of the organ is organized in a strictly hierarchical manner, providing support to the parenchyma.
The dense tunica albuginea on one side of the organ projects deeply inward, forming a massive thickening — the mediastinum testis (mediastinum testis). This mediastinum serves as the central supporting rod of the entire structure. From it, thin connective tissue septa — septula testis — radiate toward the periphery (back to the tunica albuginea).
These septa divide the entire internal parenchyma into isolated compartments — lobules of testis (lobuli testis). There are on average about 250 such lobules in one testis of an adult man.
Functional elements of the parenchyma
The entire parenchyma of the organ has a tubular structure. Inside and between the lobules lie three key functional components:
- Spermatogenic tubules: The primary site where the continuous process of formation and maturation of male gametes (spermatozoa) takes place.
- Excretory tubules: These represent the initial link of a complex elimination system. Their primary histological function is the storage (temporary accumulation) and subsequent evacuation of formed spermatozoa outside the gonad.
- Interstitial cells: These elements are located not inside the tubular structures, but in the connective tissue stroma between the tubules. They perform the endocrine function of the organ — the active synthesis of male sex hormones (testosterone and its various derivatives).
Briefly: answers to topical questions
What types of cells form the wall of the convoluted seminiferous tubule?
The wall of the convoluted seminiferous tubule comprises the spermatogenic epithelium and proper sheath.
Cellular elements confirmed by sources:
- Sertoli cells (sustentocytes, follicular cells) — form the "framework" of the spermatogenic epithelium.
- Spermatogenic lineage cells — spermatogonia and early spermatocytes in the basal compartment; subsequent stages of germ cell development are located in the adluminal compartment.
- Myoid cells of the proper sheath of the seminiferous tubule.
What is the sequence of intratesticular excretory pathways from the convoluted tubules to the epididymis?
The sequence of tubules from the spermatogenic tissue to the elimination system begins within the testis and transitions into the epididymis.
- Straight tubules (tubuli recti) — a short continuation of the convoluted tubules.
- Tubules of the rete testis (rete testis) — a system of anastomosing channels in the mediastinum testis.
- Efferent ductules (ductuli efferentes) — emerge from the rete testis and form the head of the epididymis.
- Duct of the epididymis (ductus epididymidis) — coils repeatedly and transitions into the vas deferens.
What stages does the process of spermatogenesis include?
In the mature human testis, spermatogenesis is subdivided into four main phases (stages) corresponding to the types of developing cells.
- Proliferation — mitotic division of spermatogonia, lasting about 2 weeks.
- Growth — cell enlargement and transformation into a primary spermatocyte.
- Maturation — meiotic division of spermatocytes resulting in the formation of spermatids, taking about 1 month.
- Spermiogenesis (Formation) — morphological maturation of spermatids into spermatozoa without cell division, lasting about 1 month.
What structures form the blood-testis barrier?
The blood-testis barrier is a multi-layered structure extending from the blood vessel to the lumen of the seminiferous tubule.
Components of the barrier:
- Testicular capillary endothelium (fenestrated) and its basement membrane.
- Interstitial tissue (narrow layers).
- Wall of lymphatic vessels (sinusoidal capillaries).
- Proper sheath of the seminiferous tubules.
- Basement membrane of the spermatogenic epithelium.
- Tight junctions (zonula occludens) between the processes of neighboring Sertoli cells — the key occluding link of the barrier.
Class and exam questions
Which tunics are directly fused with the testicular tissue?
Only the two innermost tunics are tightly fused to the organ parenchyma: the tunica albuginea and the visceral layer of the tunica vaginalis.
What is the main histological feature of the dartos tunic (tunica dartos)?
Its subcutaneous tissue contains absolutely no fat, but includes bundles of smooth myocytes.
Where exactly is testosterone produced?
Interstitial cells, located in the connective tissue stroma between the tubules, are responsible for the synthesis of testosterone and its derivatives.
Which structure acts as the «central axis» of the organ?
The mediastinum testis (mediastinum testis), which is a thickening of the tunica albuginea projecting into the parenchyma.
What else to study on this topic
- Cellular composition of the seminiferous tubules (Sertoli cells and spermatogenic epithelium)
- Histophysiology of interstitial cells (Leydig cells)
- Sequence of the testicular excretory tubules
- The process of spermatogenesis and its hormonal regulation
- Histological structure of the epididymis (epididymis)
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