Spermatozoa and spermatogenesis

Male reproductive cells - spermatozoa - are mobile cells about 70 microns long. The spermatozoon has a nucleus, cytoplasm with organelles and a cell membrane. The spermatozoon has a round head and a thin long tail. The head contains a nucleus, in front of which is a structure called the acrosome. The acrosome has a set of enzymes that are capable of dissolving the membrane of the egg during fertilization. The tail of the spermatozoon contains contractile elements (bundles of fibrils) that ensure the movement of the spermatozoon. When the spermatozoon passes through the vas deferens, liquid secretions of the sex glands are added to it: the seminal vesicles, prostate and bulbourethral glands. As a result, a liquid medium is formed in which the spermatozoa are located - this is semen. The lifespan and fertilizing capacity of human sperm ranges from several hours to 2 days.

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Spermatogenesis

Spermatozoa are formed in humans throughout the entire active period of a man's life. The duration of development and formation of mature spermatozoa from their precursors - spermatogonia is about 70-75 days. This process occurs in the convoluted seminiferous tubules of the testicle. Initially, spermatogonia, the total number of which in one testicle reaches 1 billion, intensively multiply, divide mitotically (Fig. 15), and the number of new cells (spermatogonia) increases. Subsequently, part of the spermatogonia retains the ability to divide and maintains the population. Other spermatogonia divide twice more in the form of meiosis. As a result, from each such spermatogonium, which has a diploid (double) set of chromosomes (n=46), 4 spermatids are formed. Each of these spermatids receives a haploid (single) set of chromosomes (n=23). Spermatids gradually turn into spermatozoa. During this complex process, the spermatids undergo structural changes: they lengthen, and a thickened head and a thin, long tail are formed. The head of the sperm forms a compacted body, the acrosome, containing enzymes that, when they meet the female reproductive cell (egg), destroy its membrane, which is important for the sperm to penetrate the egg. If the acrosome is underdeveloped or absent, the sperm is unable to penetrate the egg and fertilize it.

The formed spermatozoa enter the lumen of the convoluted seminiferous tubules of the testicle and, together with the fluid secreted by the walls of the seminiferous tubules, gradually move towards the epididymis, which also serves as a reservoir for spermatozoa. The number of formed spermatozoa is enormous. 1 ml of sperm contains 100 million spermatozoa. These are mobile cells, the speed of their movement along the tubules is about 3.5 mm per 1 min. In the female genital tract, spermatozoa remain viable for 1-2 days. They move towards the egg, which is due to chemotaxis.