Special Histology and Embryology: Practical Course - V. K. Napkhanyuk 2001

Reproductive System
Male Reproductive System
Testes

The Male Reproductive System (organa genitalia masculina) comprises the male Gonads (testices, deferent ducts) and Accessory structures of the male reproductive system (Seminal Vesicles, Prostate Gland, Bulbourethral Glands, Penis).

The testes, or testicles (Testis), are the primary male gonads responsible for The production of male Gametes and the male sex hormone.

Externally, the greater part of the testis is covered by a serous membrane—the Peritoneum—beneath which lies the tunica albuginea, a Cytology/practical/45.html">Dense Connective Tissue capsule.

At the posterior border of the testis, the tunica albuginea thickens to form the Mediastinum testis, from which connective tissue septa extend into the gland, dividing it into lobules. A lobule serves as the Structural and functional unit of the testis. Each testis contains 250–300 lobules.

Each lobule contains 1 to 4 tightly packed convoluted seminiferous tubules. A convoluted seminiferous tubule measures from 30 to 70 cm in length and 150–250 µm in diameter.

Approaching the mediastinum, the tubules merge and become straight (tubulet recti). Within the mediastinum, they connect with the rete testis. From this network, 10–12 efferent ductules emerge and empty into the duct of the Epididymis. The wall of the convoluted seminiferous tubule consists of three layers:

1) the basal layer (stratum basale), formed by a network of Collagen fibers separated from the internal Contents of the tubules by a basement membrane;

2) the myoid layer (stratum myoideum), composed of specialized myoid Cells containing Actin filaments, yet distinct from typical smooth Muscle cells;

3) the fibrous layer (stratum fibrosum), which comprises two parts: an inner acellular layer consisting of the basement membrane and myoid cells, and an outer layer formed by fibroblast-like cells.

The connective tissue located between the seminiferous tubules contains Blood and Lymphatic capillaries that facilitate Metabolic exchange between the blood and the spermatogenic epithelium. The Structure/83.html">Structural elements of the convoluted tubule wall, endothelial cells, and the parabasal layer of the blood Capillary Wall together form the blood-testis barrier, which ensures the selective permeability of various chemical compounds into the lumen of the convoluted seminiferous tubule. The blood capillaries are accompanied by connective tissue septa housing the testicular endocrinocytes (Leydig cells), which synthesize the hormone testosterone.

The internal environment of the convoluted seminiferous tubule is formed by two Cell populations that constitute the epitheliospermatogenic layer: 1) supporting cells, or sustentocytes (Sertoli cells, epiteliocytus sustentas), which are pyramidal in shape, rest on the basement membrane, and reach the lumen with their apices (micrograph 45). The Cytoplasm of these cells contains all standard Organelles, and their cell membrane forms numerous invaginations. Tight junction complexes are established between adjacent cells, dividing the spermatogenic epithelium into two compartments: an outer (basal) compartment and an inner (adluminal) compartment. The supporting cells provide the microenvironment necessary for differentiating Germ Cells and isolate the developing germ cells from toxic substances and various Antigens;

2) spermatogenic cells (cellulae spermatogenicae), represented by stem cells, spermatogonia, spermatocytes, spermatids, and spermatozoa. Both populations maintain a close morphofunctional relationship.

Spermatogenesis

Spermatogenesis (spermatogenesis) is The process of male gamete formation that takes place within the convoluted seminiferous tubules and consists of four consecutive stages or phases:

1. Multiplication (proliferation). This phase involves the mitotic division of spermatogonia, which include slowly dividing stem cell subpopulations and more rapidly dividing hemistem cell subpopulations;

2. Growth. In this phase, spermatogonia cease dividing and differentiate into primary spermatocytes. During this period, they migrate to the adluminal compartment of the convoluted tubule, increase in volume, and enter the first meiotic division. The prophase of the First Division is prolonged and comprises 5 stages: leptotene, zygotene, pachytene, diplotene, and diakinesis.

3. Maturation. Upon completion of the growth phase, the primary spermatocyte enters metaphase of the first meiotic division (first maturation division), resulting in The formation of a secondary spermatocyte—a cell with a haploid chromosome set. The secondary spermatocyte is smaller in size and is located in the middle and more superficial layers of the spermatogenic epithelium. Prior to the second maturation division, neither DNA Synthesis nor chromosomal duplication occurs in the secondary spermatocyte. The second (equational) maturation division yields a spermatid—a cell with a haploid set of Chromosomes.

4. Spermiogenesis (formation). In this phase, spermatids transform into spermatozoa (micrograph 46).

The epididymis (epididymis) consists of a tightly coiled tube—the duct of the epididymis—which ensures sperm transport, while the final differentiation of spermatozoa takes place within its lumen. The epididymis comprises a HEAD, a body, and a tail.

Connective tissue septa divide the parenchyma of the epididymis into lobules. The wall of the epididymal duct consists of three tunics: a mucosa, lined with a Pseudostratified columnar epithelium composed of two cell types (stereociliated/tufted cells and basal cells); a muscular tunic; and an adventitial tunic.