Androgeos.cz

The testis of a newborn is about 1 cm long and its weight is about 2 g. It grows slowly (ca to 12 g) until puberty, when it gains weight quickly and reaches its definitive size after the 20th year of life.

It is formed in the abdominal cavity and during the foetus development it descends through the inguinal canal into the scrotum. In the scrotum, it is deposited in an almost vertical position. Its size varies with age and hormonal stimulation. The upper pole (extremitas superior) is inclined slightly forwards and outwards, the lower pole (extremitas interior) slightly backwards and inwards. The left testis is situated about 1 cm lower than the right one. The surface of the testis is covered by peritoneum with the exception of the posterior margin (margo posterior), where it is superimposed by epididymis. The peritoneal cover has two leaves, which are separated by a cavity (cavum serosum scroti). The lower pole of the testis is connected with the base of the scrotum by a fibrous band (ligamentum scrotale, or gubernaculum testis).

The surface of the testis is formed by a fibrous membrane (tunica albuginea). Towards the depth, septa derive from it (septula testis), dividing the testis into 200-300 conical lobules (lobuli testis). Their apices are turned opposite to the posterior margin, where mediastinum testis with a network of tubules is formed (rete testis). From rete testis, 10-20 efferent ductules (ducti efferentes testis) extrude into the hilus, forming the head of the epididymis. The lobules contain coiled seminiferous tubules (tubuli seminiferi contori), which close to the lobule apex fuse into one direct tubule (tubulus rectus). Seminiferous tubules are 30-70 cm long and end in rete testis.

The tubule walls are formed by a thin layer of connective tissue, basal lamina and seminiferous epithelium. The epithelium contains two cell types: spermiogenic cells in various developmental phases and supportive Sertoli cells.

Spermiogenesis proceeds in several subsequent stages and includes proliferation, mitosis and cytodifferentiation of genital cells. It occurs in the tubule walls in temporal-spatial waves. It starts close to the basal lamina and proceeds in elongated spiral towards the lumen of tubules. In the intervals 200-300 µm, subsequent waves of spermiogenesis start. This spatial organization of individual spermiogenesis stages determines diverse appearance of the tubules and allows for continuous formation of spermatozoa. The entire process from stem spermatogonia until mature spermatozoa in the ejaculate lasts for a minimum of 82 days in man. It is estimated that ca 1 million of spermatozoa leave the testis every hour.

Spermiogenesis is ensured and enabled by Sertoli cells. They form a barrier between blood and cells of the spermatogenic line and mediate the metabolism of genital cells. They also form the testicular fluid and sythesize the androgen-binding protein. Sertoli cells are very resistant, but in the period of genital maturity they stop dividing and their renewal is impossible. They represent the limiting factor for spermiogenesis.

The interstitium surrounding the tubules contains thin connective tissue, Leydig cells, mast cells, macrophages and a rich network of fenestrated blood capillaries and lymph veins. Interstitial Leydig cells produce testosterone. Its production is influenced by the luteinizing hormone of the pituitary.

It is situated above the upper testis pole and on its posterior side. Near the lower testis pole it bends backwards and upwards and passes into vas deferens (ductus deferens). The epididymis head (caput epididymidis) is formed by 8-12 testicular efferent ductules (ductuli efferentes testis). Each ductule is coiled in one lobule (lobulus epididymidis) and is surrounded by connective tissue. Fusion of efferent ductules leads to formation of a coiled and folded tube (ductus epididymidis), which forms the corpus and tail of the epididymis.

The walls of testicular efferent ductules are formed by connective tissue and circularly organized smooth muscle cells. The ductule epithelium contains cells without cilia and ciliary cells. The cilia swing forwards from the testis and ensure the sperm movement.