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Spermatozoa and spermatogenesis
Last reviewed: 20.11.2021
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Male germ cells - spermatozoa - are mobile cells of about 70 μm in length. The spermatozoon has a nucleus, a cytoplasm with organelles, and a cell membrane. In the spermatozoon, a round head and a thin long tail are distinguished . The head contains a nucleus, in front of which there is a structure called acrosome. The acrosome has a set of enzymes that can dissolve the egg shell during fertilization. The tail of the spermatozoon contains contractile elements (bundles of fibrils), which ensure the movement of the sperm. When the sperm passes through the vas deferens, liquid secrets of the genital glands are added to it: seminal vesicles, prostate and bulbourethral glands. As a result, a liquid medium is formed in which spermatozoa are found - this is sperm. Life expectancy and fertility of human spermatozoa is from a few hours to 2 days.
[1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13]
Spermatogenesis
Spermatozoa are formed in a person during the entire active period of a man's life. The duration of development and formation of mature spermatozoa from their predecessors - spermatogonia is about 70-75 days. This process occurs in the convoluted seminiferous tubules of the testicle. Initially, spermatogonia, the total number of which reaches 1 billion in one testicle, multiply intensely, divide by the mitotic pathway (Figure 15), while the number of new cells (spermatogonia) increases . Later, a part of spermatogonia retains the ability to divide and maintains the population. Other spermatogonia are divided twice more in the form of meiosis. As a result, of each spermatogonia with a diploid (double) set (n = 4b) of chromosomes, 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 structures in the spermatids are restructured: they are lengthened, they have a thickened head and a thin long tail. At the head of the spermatozoon, a compacted body - an acrosome, containing enzymes is formed, which, when encountered with a female germ cell (egg), destroy its shell, which is important for penetration of the sperm into the egg cell. When the acrosome is underdeveloped or absent, the spermatozoon is unable to penetrate the egg and fertilize it.
The formed spermatozoa fall into the lumen of the convoluted seminiferous tubules of the testicle and, together with the fluid released by the walls of the seminiferous tubules, gradually move toward the epididymis, which also serves as a reservoir for spermatozoa. The amount of spermatozoa is enormous. In 1 ml of sperm contains 100 million spermatozoa. These are mobile cells, the rate of their progress along the tubules is about 3.5 mm per minute. In the female reproductive tract, spermatozoa remain viable for 1-2 days. They move toward the egg, which is due to chemotaxis.