SPERMATOGENESIS

From Big Medical Encyclopedia

SPERMATOGENESIS (Greek sperma, spermat[os] seed + genesis origin; synonym spermatopoez) — the complex cyclic process of cellular transformations happening in gyrose seed tubules of testicles as a result to-rogo mature men's sex cells (spermatozoa, or the spermiya) capable to fertilization are formed.

Histologic studying of S. began since the end of 19 century. Important data on division of spermatogenetiche-sky cells published in 1897 Mr. Lenkhonipek (M. Lenhossek). The decisive contribution to development of modern ideas of kinetics, dynamics and morphology of this process was brought by Le Blond's researches (Page P. Leblond) and Y. Clermont begun in the 50th 20 century.

Development spermatozoa (see) occurs in gyrose seed tubules of the testicles covered by various generation of a spermatogenic epithelium — spermatogones, spermatocytes and spermatids, to-rye are called also cells of a spermatogenesis.

Stem cells of S. are spermatogones — the round cells with an oval kernel located on a basal membrane of gyrose seed tubules near supporting cells (Sertoli's cell). In the period of embryonic development and at children's age of a spermatogone (primary) share mitotic, giving rise to additional spermatogones. After approach of puberty a part of spermatogones enters the Village. Other part of spermatogones continues to share mitotic, making spermatogones for the subsequent Page. During each spermatogenic cycle there are several waves of a mitosis (see. Mitosis ), and after everyone the quantity of the cells which entered S. doubles. The youngest spermatogones (type A) having a light kernel and a thin nuclear envelope consistently share, giving affiliated to generation (A1, A2, A3 and A4). In each new generation time of premitotic synthesis of DNA is extended. Spermatogones of a transition type are formed of spermatogones of the A4 type as a result of division, after division to-rykh there are spermatogones of type B having larger glybk of chromatin and thicker nuclear envelope. Spermatogones of type B are also presented by one generation; their daughter cells increase in sizes and, having finished a growth period, turn into primary spermatocytes, to-rye leave a layer of spermatogones and move closer to a gleam of tubules.

As a result of division of primary spermatocytes (see. Meiosis ) secondary spermatocytes are formed. After a short dormant period there is the second division of spermatocytes as a usual mitosis, as a result to-rogo spermatids, being predecessors of spermatozoa are formed. At division of secondary spermatocytes of synthesis of DNA does not occur therefore spermatids contain a haploid set of chromosomes including 22 autosomes and one sexual X-or a Y-chromosome. Spermatids represent rather small cells having a kernel to dia. 5 — 6 microns.

Transformation of a spermatid into a spermatozoon includes the complex processes of growth and a differentiation of cells of S. which are not followed by cellular division. Process of formation of spermatozoa happens in close contact with supporting cells. Supporting cells define conditions of development of the sharing spermatogenic elements, they emit the complex chemical substances promoting a normal current of S., provide food of the ripening spermatids. At transformation of a spermatid the kernel moves to an upper part of the cell taking the oval form and turns into a head of a spermatozoon, to-ry dumps the most part of cytoplasm by this time. Golgi's complex located near a kernel goes to an upper pole of a cell and forms the acrosome surrounding a kernel from above. From a proximal tsentriola there is a trailer body, and from distal — the axial filament surrounded with a thin cytoplasmatic cover. The mitochondrions which are in cytoplasm are localized in a neck of a spermatozoon and form its motive device (spiral thread). The ripened spermatozoa separate from cytoplasm of supporting cells, accumulate in a gleam of a seed tubule and with current of the liquid which is also produced by supporting cells get to the canal of an epididymis where find mobility. Normal S.'s cells are in the ratio: spermatogones make up to 17%, spermatocytes — to 30%, a spermatid — about 50%. Time, during to-rogo a spermatozoon completely develops from a spermatogone of type A, makes 72 — 74 days.

The page and products of hormones in a small egg are controlled gipotalamo-pituitary system (see). On S. hormones of a number of closed glands make impact, among to-rykh anterior pituitary hormones — gonadotrophins are on the first place (see. Gonadotropic hormones ). The village to a stage of primary spermatocytes does not demand participation androgens (see) or gonadotrophins, but they are necessary for the subsequent stages of maturing. Decrease in formation of gonadotrophins is led to S. Sushchestvuyet's termination by difficult interrelation between hormonal functions small egg (see) and other closed glands: a hypophysis, adrenal glands, a thyroid gland, etc. Besides, there is an opinion on influence on Page. seed bubbles (see) and prostate (see). At elderly people reduction of formation of spermatozoa, apparently, is caused by fading of gonadotropic function of a hypophysis and deterioration in a trophicity of a small egg.

Under the influence of various reasons the spermatogenic cycle can be broken, i.e. there is a so-called disorganization of a spermatogenic epithelium. Most often S. stops at a stage of spermatocytes, is more rare at a stage of spermatogones or spermatids, spermatozoa in these cases are not formed (see. Azoospermism ). At a hypospermatogenesis the quantity of cells of S. is in a varying degree reduced, spermatozoa meet a little, even teratoid forms prevail morphologically changed or (see. Necrospermia ). S.'s changes can be caused by genetic defeats (a cryptorchism, etc.), hormonal factors (pituitary or neurohormonal diseases), inflammatory diseases (orchitis), radiation injuries, etc. At recognition of disturbances of S. the somatic research, including urological is necessary (see. Infertility ), a research of an ejaculate (see. Sperm ), and it is frequent also a biopsy of a small egg.



Bibliography: Burnasheva S.A., etc. Modern problems of a spermatogenesis, M., 1982; Kagan S.A. Sterility at men, L., 1974, bibliogr.; Molnar E. The general spermatology, the lane with it., Budapest, 1969; Ruzen e e e e e e e E. Spermatogenez at animals, the lane with English, M., 1980; Surikova K. K. Cytochemical studying of a cycle of a seed epithelium at a white mouse, Dokl. Academy of Sciences of the USSR, t. 112, No. 4, page 756, 1957; Heller of Page G. ampere-second 1 e r m about n t Y. Kinetics of the germinal epithelium in man, Rec. Progr. Horm. Res., v. 20, p. 545, 1964; Leblond C. P. a. Clermont Y. Spermiogenesis of rat, mouse, hamster and guinea pig, Amer. J. Anat., v. 90, p. 167, 1952.


V. V. Mazin.

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