SEXUAL FUNCTIONS

From Big Medical Encyclopedia

SEXUAL FUNCTIONS — the complex of processes including maturing of sex cells, formation of sexual motivations, a sexual behavior, sexual intercourse, processes of fertilization, pregnancy, childbirth, a lactation and the subsequent education of posterity. Independent articles are devoted to a number of elements of sexual function (e.g., Pregnancy , Ovulation , Oogenesis , Fertilisation , Sexual intercourse , Spermatogenesis ). The functional system providing regulation of these processes has complex structure. A basis of its structure is the neuroendocrinal complex — hypothalamus (see), hypophysis (see), gonads (see).

In fabrics where hormonal effects are implemented, there is advanced information, edges on feed-backs is transferred to c. N of page. Here information «is processed» and comes to the sexual centers of a hypothalamus. By means of rileasing-hormones (see. Hypothalamic neurohormones ) the hypothalamus precisely regulates secretion tropny hormones of a hypophysis (see), and through it — secretion of closed glands, providing in an organism the level of hormones, optimum for each age period and constantly changing life situations.

10 hypothalamic rileasing-hormones are known. One of them stimulate (liberina), others brake (statines) synthesis and release of hypophyseal hormones. Rileasing-gormony are developed by neurons of various kernels of a hypothalamus and on axons are transported in a median eminence of a neurohypophysis, through a cut get into loops of primary haemo capillary network. The blood enriched with rileasing-hormones flows on a portal venule of a hypophysis in a front share of a hypophysis (an adenohypophysis, T.). So, Hypothalamic control is exercised by a humoral way endocrine system (see).

At women follicle-stimulating (FSG) and luteinizing (LG) hormones of a hypophysis (see. Luteinizing hormone , Follicle-stimulating hormone ), exerting regulating impact on gonads, are under control of the tonic and cyclic centers of a hypothalamus. The tonic center supports continuous basal secretion of FSG and LG and by means of rileasing-hormones foul - Berinum and a lyuliberin controls biosynthesis and release of gonadotrophins (see. Gonadotropic hormones ) in the quantity sufficient for development of follicles in ovaries (see) between ovulations (see). The cyclic center joins in the control system of gonads only in the period of an ovulation, providing ovulatory emission of L G from a hypophysis, a rupture of the ripened follicles, supporting formation yellow body (see). Thus, against the background of constantly functioning tonic center the cyclic center joins in system pulsewise (discretely) only for implementation of an ovulation. In a female body the beginning of reproductive function in the pubertal period and its further implementation on протяя^ении all childbearing age is defined by this center.

Level of sex hormones in blood, extent of their utilization in fabrics determine functional activity of the hypothalamic centers by the principle of the return negative and positive bonds. Information on efficiency of effect of hormones arriving from the periphery determines work as all gipotalamo-pituitary system (see).

At males already at early stages of an embryogenesis androgens (see), produced by testicles, block development of the cyclic center. But if to remove laying of a small egg, then development of a hypothalamus will go on female type, i.e. with differentiation of the cyclic center and cycle variations of gonadotropic hormones. In a male body the tonic center which by means of FSG and L G supports the level determined for each age constantly functions spermatogenesis (see) and biosynthesis of androgens.

The arrangement of the sexual centers of a hypothalamus is defined rather precisely. A large number foul - Berinum and a lyuliberin it is concentrated in an outside zone of a median eminence of a neurohypophysis and average medial department of a hypothalamus (intermediate hypothalamic area, T.), including are-kuatnoye (arc-shaped) kernel, a front periventrikulyarny kernel and a medial part of the retrokhiazmatichesky area. The rileasing-hormones which are formed in perikaryon of neurons flow down on axons in a median eminence of a neurohypophysis where they are temporarily deposited and as required come to portal system of blood supply of a hypophysis, stimulating release of FSG and L G. In a median eminence the highest concentration of a lyuliberin, more than by 7 times exceeding its contents in an arkuatny (arc-shaped) kernel is found.

The role of the tonic center in regulation of gonadotropic hormones of a hypophysis carries out average medial department of a hypothalamus. At animals after operation of a deafferentation (full isolation) of this part of a hypothalamus the concentration of FSG and L G sufficient for stimulation of development in ovaries of follicles, but not capable to induce an ovulation is maintained. As a result ovaries undergo polycystic (polyfollicular) regeneration over time, the permanent phase of an estrus (a continuous spout) is established, and develops infertility (see). These data demonstrate that the tonic center has functional autonomy and is capable to support a long time basal secretion of FSG and L G.

The cyclic center is localized in preoptichesky area (the predzri-telny field, T.). In animal experiments it is shown that preservation of communication between average medial department of a hypothalamus (the tonic center) and preoptichesky area does not break at females of a sexual cycle with a full-fledged ovulation. The irritation of preoptichesky area causes an ovulation. In the period of a spontaneous ovulation the maximum activity in preoptichesky area is noted. Its destruction warns an ovulation. Here the high content of a lyuliberin is revealed, a cut changes according to a sexual cycle and a circadian (daily allowance) rhythm of gonadotrophins.

Among the structures making in total the cyclic center, the dominating role is played by a supra-hiazmatichesky kernel [a supraoptiche-eky (nadzritelny) kernel, T.] hypothalamus.

The signal to ovulatory emission of a lyuliberin from depot of a median eminence of a neurohypophysis comes from the cyclic center to the tonic center. It is preceded by predovu-lyatorny increase in secretion estrogen (see) which by the principle of a positive feed-back include the cyclic center in system.

The hypothalamic sexual centers, having a certain functional autonomy, are under control of a number of structures of c. N of page and first of all an amygdaloid nucleus (see. Basal kernels ) and hippocampus (see), neurons to-rykh carry out reception of level of steroid hormones. Kernels of an amygdaloid nucleus render the influence on the Hypothalamic centers both stimulating, and oppressing, and the stimulating influences proceed from medial and cortical (a cortical and medial part, T.), and inhibiting — from basal and lateral (a bazalnolateralny part, T.) kernels of an amygdaloid nucleus. Destruction of the last at immature females leads to premature sexual development. The hippocampus oppresses not only a spontaneous ovulation, but practically any increase in luteinizing hormone caused in an experiment. In regulation of gonads it is possible to allocate two systems, opposite on action: mezentsefalon-hippocampal and mezentsefalon-amygdaloid. The first carries out inhibiting, the second — the stimulating control over gipotalamo - pituitary hollow howl system.

The epiphysis has the powerful braking effect on the sexual centers of a hypothalamus (see. Pinus ). Children at injuries have heads, the infections, tumors breaking functions of an epiphysis premature sexual development is noted (see. Hypergenitalism ). As a result at boys in the first years of life generative organs reach the youthful level of development, and at girls — there come menstrualnopodobny bleedings.

An extremely important role in regulation of a reproductive system (see. Urinogenital system ) belongs to a cerebral cortex (see). Physical and emotional stresses, various extreme situations can block an ovulation and sharply inhibit a spermatogenesis. Cases mass are known, e.g. amenorrheas (see) at women in wartime, the military amenorrhea which received the name.

The amygdaloid complex, a hippocampus and some other structures in total also participate in the central regulation of sexual functions. In neuroendocrinal system is adjusted activity of the hypothalamic centers which. in turn, through tropny hormones of a hypophysis regulate secretion of hormones of closed glands, supporting the level of hormones, optimum for specific conditions, in fabrics.

The hypothalamus is not only the central component of system regulating production of hormones, but it possesses also the defining role in formation of a sexual behavior. So, at implantation to the castrated males to the preoptical area testosterone (see) their all complex of the behavioural reactions connected with copulation is recovered. Introduction of androgens to other areas of a hypothalamus significantly does not influence a sexual behavior of the castrated males. At females destruction of preoptical and front hypothalamic kernels sharply oppresses sexual activity and causes loss of ability to pairing. Replacement therapy by estrogen does not recover at them characteristic sexual desire. The irritation at males of kernels of the lateral hypothalamic field strongly activates sexual desire (see) is also followed by an erection (see. Erection ). At females the irritation of back departments of the ventro-medial hypothalamic kernel which is efferently connected with front hypothalamic area sharply stimulates sexual desire and induces a premature ovulation. In a hypothalamus structures which exert the inhibiting impact on sexual development and a sexual behavior are found.

The differentiation of the sexual centers of a hypothalamus occurs during the embryonal and post-natal periods ontogenesis (see). Disturbance of this process by administration of hormones often completely perverts a sexual behavior. So, administration of testosterone or corticosteroids (see) females of rats in the first 7 — 10 days after their birth leads to the fact that having matured, they show a men's sexual behavior. Injections of androgens to pregnant females cause signs in female posterity hermaphroditism (see) or men's sexual behavior. The females receiving estrogen in the first day after the birth in adulthood lose adequate sexual behavior. Estrogenization of males during the post-natal period sharply brakes sexual activity, reduces number of copulations. Thus, introduction sexual, as well as others, hormones in prenatal and early post-natal the periods breaks a differentiation of the hypothalamic centers and respectively character of a sexual behavior.

Sex hormones through the ascending activating influences of the hypothalamic centers directionally influence various structures of a brain, including also bark of big hemispheres, and carry out a role of a peculiar arranger of sexual desire.

As the dominating motivation sexual desire, in turn, causes considerable changes in an organism: sensitivity of receptors of sense of smell, sight, hearing, skin and especially erogenous zones — certain parts of a body increases, the irritation to-rykh causes sexual excitement. At men erogenous zones are external genitals. Women an erogenous zone can have any part of a body, but more often it is genital area (including a clitoris, a vagina, a neck of uterus), mammary glands, lips, an oral cavity, a neck, lobes of ears, inner surfaces of hips.

At the person character of sexual behavior is built up in the specific social environment. Its important factor is correct sex education (see) young men and girls, especially during saturation of an organism sex hormones (see), a strong indication to-rogo are sexual frustrations — mutual sexual caress. Sexual excitement at frustrations is limited at men to an erection, and at women, as a rule, rush of blood to generative organs. Item f. — it is the most difficult complex of physical and moral factors, instinctive rituals and uslovnoreflektorny reactions.



Bibliography: Anokhin P. K. Fundamental issues of the general theory of functional systems, M., 1971; Biochemistry of hormones and hormonal regulation, under the editorship of N. A. Yudayev, page 11, M., 1976; Vunder P. A. Endocrinology of a floor, M., 1980; Mechanisms of hormonal regulations and a role of feed-backs in the phenomena of development and a homeostasis, under the editorship of M. S. Mickiewicz, M., 1981; Chazov E. I. and Isachenkov V. A. Epifiz, the place and a role in system of neuroendocrinal regulation, M., 1974; Sawyer Ch. Some recent developments in brain-pituitary-ovarian physiology, Neuroendocrinology, v. 17, p. 97, 1975.


I. I. Dedov.

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