Spermatozoa

SPERMATOZOA (germ cells, seed cells, seminal threads), male reproductive cells of most animals, as well as some plants. First discovered in seminal fluid by Leiden student Hamen (1677) and described by Leeuwenhoek. The structure of spermatozoa in most animals is similar. The most characteristic undulating, flagellar form occurs at various levels of the zoological ladder from animals with external fertilization to mammals and humans inclusive. Deviations from this basic type occur in the form of spermatozoa of various shapes (crustaceans, turbellarians, etc.). In typically structured spermatozoa (including humans), the following are distinguished: the anterior, usually expanded part (head), the narrow transitional part (neck), and the posterior, thinned part (tail or whip). In the head part is located a compact, chromatin-rich nucleus - the carrier of hereditary properties of the paternal organism. The shape of the head in some animals (mammals) is disc-shaped, in others it is elongated (birds) or even spiral-shaped (amphibians and some birds). In humans, the shape en face is elliptical, in profile it is pear-shaped, with the expanded part directed backward. On the anterior part of the head a protrusion is observed (either needle-shaped or in the form of a crescent-shaped cap) - the perforatorium, which some researchers, apparently without sufficient grounds, assign the role of a battering ram in penetrating the egg cell membrane. The neck of the human spermatozoon, a short transitional part, represents a constriction between the head and tail. In the tail is located the motor apparatus of the spermatozoon - a contractile thread, which consists of numerous finest fibrils connected by a small amount of interstitial substance. The total length of the human spermatozoon is 50-60 μ. The shape and size of spermatozoa can vary not only among different representatives of the zoological series, but also within the same species and even within the same ejaculate (dimorphism, polymorphism). The latter can be explained by the degree of maturity of spermatozoa, as well as developmental abnormalities, which according to Goldschmidt in a certain measure serves as an indicator of degeneration of the organism. The nature of movement approaches ciliary; flagella contract in one plane and in one direction, not alternately in both directions. Usually a new contraction begins before the previous one has had time to pass as a wave along the entire tail, and for this reason the tail takes on a snake-like appearance (Brunn). Spermatozoa of most animals with external fertilization perform spiral movements, spermatozoa of animals with internal fertilization - rectilinear. Rectilinear movement is achieved by rotation of the spermatozoon around its longitudinal axis. Due to frequent contractions of the flagellum (20 or more beats per second), the locomotor ability of spermatozoa is relatively large. For example, in amphibians (frog) it is 30 μ, in birds (pigeon) - 20 μ, in mammals (mouse, human) - 50-60 μ per second. At the same time, the speed of movement of spermatozoa is very variable and obviously depends on a number of factors: the degree of maturity of spermatozoa, the density of the ejaculate, temperature, etc. According to Rohleder, the locomotor ability of seminal threads from the same person varies greatly: from 0.7 mm to 4.5 mm per minute. Atypical motility (circular, oscillatory, backward) can be observed for various reasons (weakening of motility, agglutination, etc.). - The direction of movement of spermatozoa is determined by their sensitivity to the effects of external physical factors, which is expressed in the form of rheotaxis and thigmotaxis. The first is characterized by the movement of spermatozoa against the current of fluid, the second - by their accumulation on the surface of foreign bodies. The direction of spermatozoa in the female reproductive tract is probably determined by rheotaxis, where there is a weak current of fluid from the higher parts to the lower parts, as well as the beating of cilia in the same direction. The direct meeting of spermatozoa with the egg cell is apparently of a random nature, since chemotaxis of spermatozoa with respect to products secreted by the egg has not been detected. - Spermagglutination - the sticking together of sperm cells into larger or smaller agglutinates - is a sufficiently characteristic property of spermatozoa. Occurring to one degree or another in a completely normal and fresh ejaculate, spermagglutination is most fully developed under the influence of changes in the physicochemical properties of the environment: changes in the composition and ratio of salts, concentration of hydrogen ions, etc. Agglutination is especially noticeable under the influence of normal blood serum due to the presence of auto and iso-spermagglutinins in it (London, Bernstein, Lazarev). - The energy metabolism of spermatozoa is characterized, along with intense oxygen absorption (Gray), by the simultaneous accumulation of lactic acid (Bernstein). Obviously, the high activity of spermatozoa outside the reproductive tract leads to the fact that the powerful oxidative system of the cell (in test tube conditions) proves insufficient to cover the need for energy metabolism. The zone of temperature stability of spermatozoa is relatively high. On average, for spermatozoa of warm-blooded animals it is in the range from 0 to 40°. Outside this zone, a decrease in temperature is better tolerated than an increase. Heating above 40° causes rapid death of spermatozoa. The optimal temperature for the survival of spermatozoa is in the range of 10-15° (Walton). Rays of different wavelengths affect sperm differently. The action increases in the direction from the red part of the spectrum to the violet. Death occurs most rapidly from ultraviolet rays. Scattered sunlight has no noticeable effect. The relationship to osmotic pressure is determined by the optimal 'zone', which for spermatozoa of animals with external fertilization is within the limits of osmotic pressure of blood serum. Showing relatively wide osmotic stability, spermatozoa better tolerate a shift toward hypotonicity than hypertonicity. A significant increase in the molecular concentration of the solution causes an irreversible loss of motility (Gellhorn). - Spermatozoa that have passed through the epididymal canal are much less sensitive to external influences, which is expressed in a longer duration of movement in vitro than for spermatozoa from the testis (Redenz). The action of the epididymis is explained by the formation of a protective shell on the surface of the spermatozoon from the secretion of the epididymis, the so-called 'lipoid capsule'. Loeb's rule about the antagonism of cations has only limited significance for spermatozoa. The phenomena of cation antagonism (in an environment close to neutral, pH=6.5-7.2) have a weakly expressed character or are almost not observed. Systematic literature data on the effect of cations on human sperm are absent. For bull spermatozoa, the activity and duration of motility in electrolyte solutions are arranged in the following decreasing order: Na>K, Sr>NH4, Ca>Mg>Li (Bernstein). In neutral and slightly alkaline medium, the action of anions is not sufficiently noticeable. With acidification of the solution, the specific features of anions sharply manifest themselves. The duration of maintaining motility of bull spermatozoa (at pH=7.0) decreases in the following anion series: tartrate>sulfate>chloride, phosphate>bromide, iodide>nitrate>nitrite>oxalate>lactate>citrate>acetate>salicylate (Bernstein). Similar series were obtained by Gellhorn for guinea pig spermatozoa. The toxic effect of some anions of organic salts has a reversible nature. Immobilized spermatozoa regain motility after changing the reaction of the medium or replacing the solution. Spermatozoa show a high degree of stability to changes in pH of the solution. Depending on the specific features of the buffer, the optimal zone can be expanded from pH=4.5 to pH=8.0 (Beskhlebnev). According to Gellhorn, the alkaline limit of stability of frog spermatozoa reaches pH=10.0. In pure solutions of indifferent non-electrolytes (sugars), spermatozoa retain motility for a long time (Rohleder, Mettenleiter), however noticeably worse than in a mixture of salt+non-electrolyte. A number of substances from among antiseptics have a toxic effect on sperm. For example, corrosive sublimate already in a concentration of 1:300,000 completely immobilizes spermatozoa; potassium permanganate - in a concentration of 1:25,000; formalin, lysol, copper sulfate - in a dilution of 1:10,000. The duration of survival of spermatozoa in an active state outside the reproductive tract varies in different animals. In humans, spermatozoa (in vitro) can retain motility on average for 1 day, in bulls for several days, in stallions usually no more than a day. In the human vagina (depending on the nature of the vaginal environment), the duration of survival of spermatozoa ranges from several minutes (Kehrer) to several hours. In the cervix and uterus, spermatozoa can retain motility for several days (Percy) and even according to Dührsen up to 3 weeks. The latter figures cannot claim perfection and need verification. - Anabiosis of spermatozoa - a state characteristic of germ cells already under physiological conditions. For example, in the queen bee, in the receptaculum seminis, spermatozoa in a state of anabiosis can be preserved for 3 years (Siebold); in tailed amphibians (salamander) in sac-like depressions of the cloaca - 1-2 years; in bats in the reproductive tract of the female - throughout the entire winter.

In the epididymis of humans and other mammals, spermatozoa remain in an immobile state for extended periods (for several weeks) and are activated at the moment of ejaculation by the secretions of the accessory sex glands. Artificial anabiosis of spermatozoa during their storage outside the organism can be achieved through a number of methods: cooling (Krzhizhkovsky and Pavlov), the narcotic effect of certain organic salts (sodium acetate, sodium lactate), as well as the thickening of semen (Bernshtein).