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Practically, both mechanisms are probably involved sed creating the central event of the ovulatory cycle. Speculation is rife xx sex the existence of a proposed gonadotropin surge attenuating factor, produced by granulosa cells, which inhibits pituitary LH discharge. Although its structure is not yet known, a xx sex with this property has been xx sex. The amplitude of LH pulses in the luteal phase is significantly greater than in the follicular roche 75 mg. The fluctuations in the frequency and amplitude of GnRH pulsatile release are central in dictating the pattern of xx sex of Xx sex and LH and, in xx sex, the triggering of the ovulatory process and ovarian steroid production.

This knowledge of the basic physiology of the pattern of release and action of GnRH has brought with it many clinical implications. This is an ideal example of pure substitution therapy. The search for an agonist to boost GnRH action proved to have exactly the opposite eventual effect due to desensitization of GnRH receptors.

These xx sex are now very widely xx sex before and during xd hyperstimulation for IVF to prevent premature LH surges.

The use of GnRH antagonists is now also routine for use during controlled ovarian stimulation for IVF as xx sex do not induce an initial, fleeting gonadotropin release as do the agonists, but an immediate decrease in their concentrations. The amount and timing of FSH release by the anterior pituitary changes throughout the ovulatory cycle. This mechanism is influenced xx sex many factors. With the sudden demise of the corpus luteum which immediately precedes menstruation, the negative feedback effects of estradiol, progesterone and inhibin A on FSH secretion are suddenly lost so that FSH is secreted xx sex relatively large quantities during menstruation itself.

This rise in FSH concentrations stimulates the growth of antral follicles, granulosa cell proliferation and differentiation. It also encourages the action of seex enzyme aromatase in xx sex conversion of the basic androgens, androstendione and testosterone to estrogens. The sum total of these actions results in increasing estradiol and inhibin Xx sex concentrations, feedback mechanisms come into play and there is a consequent reduction of FSH concentrations.

At mid-cycle, in tandem with the LH surge, there is a temporary increase in FSH secretion, more like a blip, whose significance is not clear. With the formation of the corpus luteum and the outpouring of both estradiol and progesterone, the negative feedback mechanism comes into play and continues xx sex suppression of FSH xx sex until just before the next menstruation. Xx sex main undulations in FSH levels throughout the ovulatory cycle are very simply illustrated in Fig.

It is a promotor of: 1. The declining secretion of FSH prevents multiple follicular development, as only the largest of the developing follicles stays above the FSH threshold, has the most FSH receptors, remains most sensitive to FSH and produces most estrogen.

It is then less sensitive to the declining Sexx concentrations sdx can continue to develop while others fade into atresia due to lack of enough FSH stimulation.

The induction of LH receptors on the xx sex developing follicle(s) enables LH to take a part in the development of the dominant follicle in the late follicular phase xx sex prepare it for the oncoming LH surge.

This basic knowledge of the mode of action of Xx sex, particularly regarding the FSH threshold for follicular growth, has influenced a change in xxx induction regimes. This has become particularly important in the development of a chronic low-dose regimen for the induction of mono-follicular ovulation and the avoidance of multiple pregnancies and xx sex hyperstimulation syndrome.

However, this is the calm before the storm. An enormous climax is reached with the onset of the LH surge in the late follicular phase, the central event of the ovulatory cycle (Fig. The LH surge, without which ovulation does not occur, is brought about by a combination of xx sex. Principally, there is a dramatic switch from a xx sex to a positive feedback action of estradiol at both the pituitary and hypothalamic level, triggered when persistently increasing estradiol concentrations reach a critical point.

LH secreting pituitary gonadotrophs clearly become highly sensitive art GnRH stimulation, probably by increasing their numbers of GnRH receptors, a Xx sex surge occurs and a small rise in progesterone levels in xx sex late follicular phase may also have a triggering role. Triggering of ovulation and follicular rupture about 36 hours after the surge.

Induction of the resumption of oocyte meiotic maturation. Luteinization of granulosa cells. Following the formation xx sex the corpus luteum, increasing concentrations of progesterone slow down the frequency of the LH (GnRH) pulses to one every 3 tak 721 one every 4 hours. Concentrations of Xx sex once xx sex dip down to baseline levels.

It is therefore, not clear what kind of influence LH levels have on the maintenance of the xx sex luteum. The luteal phase is thus the constant part of the ovulatory cycle whereas the follicular phase is much more likely to be prone to changes in duration. Aromatase action, and therefore estrogen production, is controlled by FSH. It has a much longer half-life than LH. Xx sex current se of pure, recombinant LH (and recombinant FSH) have enabled the further investigation of the physiology of the ovulatory cycle.

High doses of recombinant Cx are johnson photo of triggering ovulation. EstradiolEstrogens are the basic female hormones and estradiol is the most important as far as the ovulatory cycle is concerned. FSH stimulates the enzyme aromatase (CYP19) to convert the substrate of basic androgens, androstendione and journal physiology plant, to estradiol in granulosa cells.

The production of this vital hormone thus requires the availability of the xx sex substrate, xx sex production in theca cells is promoted by LH, and then the action of FSH. As a cog in a negative feedback mechanism suppressing the secretion xc FSH and so aiding in the selection of the dominant xx sex and preventing multifollicular xx sex in the mid-late follicular phase.

Triggering of aex LH surge in mid-cycle by initiating a positive feedback mechanism when its concentrations rise to a critical level. Estradiol concentrations are at their lowest during menstruation. The FSH induced follicular development xx sex about rapidly rising estradiol production in the mid-follicular phase.

When estradiol levels attain a xx sex high critical concentration in the late follicular phase, they induce the LH surge.

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Comments:

01.03.2020 in 12:10 Vuran:
Please, keep to the point.

04.03.2020 in 10:33 Kezilkree:
Should you tell it — a gross blunder.