The LH surge, without which ovulation does not occur, is brought about by a combination of circumstances. Principally, there is a dramatic switch from a negative 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 to GnRH stimulation, probably by increasing their numbers of GnRH receptors, a GnRH surge occurs and a small rise in progesterone levels in the late follicular phase may also have a triggering role.
Triggering of ovulation and follicular rupture about 36 hours after the surge. Disruption of the cumulus—oocyte complex. Induction of the resumption of oocyte meiotic maturation. Luteinization of granulosa cells. Following the formation of the corpus luteum, increasing concentrations of progesterone slow down the frequency of the LH GnRH pulses to one every 3 then one every 4 hours.
Concentrations of LH once again dip down to baseline levels. It is therefore, not clear what kind of influence LH levels have on the maintenance of the corpus 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. Outside the tumultuous events of the mid-cycle surge, the main function of LH is to encourage the production of androgens by theca cells.
Here they meet aromatase CYP19 , whose function it is to convert them into estrogens, mainly estradiol but also estrone. Aromatase action, and therefore estrogen production, is controlled by FSH. In clinical practice, hCG has been used as an excellent substitute for the LH surge in the triggering of ovulation as it binds to the LH receptor. It has a much longer half-life than LH. The current availability of pure, recombinant LH and recombinant FSH have enabled the further investigation of the physiology of the ovulatory cycle.
High doses of recombinant LH are capable of triggering ovulation. The availability of these preparations as separate entities has prompted a large number of experiments to examine what is their exact function and necessity throughout the cycle.
Estrogens are the basic female hormones and estradiol is the most important as far as the ovulatory cycle is concerned. The synthesis of estradiol by granulosa cells is a function of the action of FSH. FSH stimulates the enzyme aromatase CYP19 to convert the substrate of basic androgens, androstendione and testosterone, to estradiol in granulosa cells. The production of this vital hormone thus requires the availability of the androgen substrate, whose 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 of FSH and so aiding in the selection of the dominant follicle and preventing multifollicular development in the mid-late follicular phase. Triggering of the 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 brings about rapidly rising estradiol production in the mid-follicular phase.
When estradiol levels attain a persistently high critical concentration in the late follicular phase, they induce the LH surge. Following ovulation, estradiol concentrations dip temporarily but are revived by corpus luteum activity. With the demise of the corpus luteum, estradiol concentrations sink rapidly to their lowest levels and invoke the FSH rise immediately preceding menstruation Fig.
A mistake of nature, hypogonadotrophic hypogonadism, in which both FSH and LH secretion are essentially missing, has provided a learning tool for the understanding of ovulatory physiology. The absence of FSH results in a lack of follicular development and estrogen production and the absence of LH in a lack of androgen substrate production. When treatment with pulsatile GnRH is administered, pure substitution therapy, everything falls into place and ovulation can be successfully induced.
If pure FSH is used to induce ovulation by direct stimulation of the ovaries, the lack of LH and therefore lack of production of androgen substrate, allows the growth of follicles but not estradiol production. Even if ovulation can be triggered by hCG or recombinant LH when a large follicle is obtained, implantation cannot occur due to the lack of estrogen stimulation on the endometrium.
Progesterone is produced by luteinized granulosa cells. Large quantities are synthesized by the corpus luteum following ovulation. Progesterone concentrations rise to a peak 7—8 days following ovulation and fall rapidly with the failure of the corpus luteum Fig. Under the influence of progesterone the endometrial glandular structures increase greatly in numbers and become more tortuous.
Progesterone also plays a role in the expression of genes needed for implantation at the level of the endometrium. Together with estradiol, progesterone suppresses pituitary gonadotropin release during the luteal phase. During this phase, FSH is synthesized and stored ready for release when freed from the inhibition imposed by progesterone and estradiol when the corpus luteum fails.
The initial rise of progesterone concentrations immediately preceding the LH surge may play a role in the triggering of this surge. The ovary is, arguably, the most dynamically, constantly changing organ in the female body during the reproductive life span Fig.
The inner, medullary or stromal section, is made up of connective tissue inundated by small capillaries and adrenergic nerves. The cortex, contains an enormous number of oocyte-containing follicles ranging from approximately , at menarche to at menopause. There is a constant state of flux in the various stages of development of the follicles from primordial an oocyte with a single layer of granulosa cells around it , through primary and secondary stages with increasing numbers of layers of granulosa cells, antral stage containing follicular fluid, to a fully fledged, pre-ovulatory follicle.
A corpus luteum can be seen in the luteal phase of the cycle and the picture is completed by the presence of corpora albicans remnants of degenerate corpora lutea.
Hormone levels shift across your menstrual cycle to gear your body up for ovulation — including luteinizing hormone LH , which is produced by the pituitary gland:.
No, there aren't any "symptoms" that come along with an LH surge specifically. But two bodily changes can clue you in to when ovulation might come for you:. Cervical mucus changes Your body produces stretchy cervical mucus, similar to an egg white in consistency, in the days before ovulation day 14 if you have a day cycle.
You can track changes in your cervical mucus in the following ways:. But because there are many factors that influence your body temperature beyond your cycle e. Aside from an ultrasound that looks at your ovaries, your LH level is the most direct way to predict ovulation because the hormone is biologically implicated in the process of ovulation.
Ovulation tests , or ovulation predictor kits OPKs , are urine tests that measure LH to help you pinpoint when your level is surging.
In this sample , though the median LH on the day before ovulation was about Another way of putting it? Visuals and text from medical textbooks indicate that there is a single, large pre-ovulatory LH surge that lasts for about 24 hours. This pattern makes two assumptions about LH around ovulation:. Estradiol a type of the hormone estrogen is produced by the follicle as it grows and levels go up quickly just before ovulation. If fertility medicines are being used to cause a woman to ovulate, estradiol levels are checked more often to keep an eye on the growth of the follicle, but it is not used to tell you when you might ovulate.
A rise in LH levels in the blood can predict when the follicle sac where the egg ripens is ripe and ready for ovulation. Because LH is released in pulses or short bursts, the LH surge is not always found by a single blood or urine test. Increased progesterone levels in the blood a week before the menstrual period usually indicates ovulation has occurred but cannot predict when it will occur. For women with irregular periods, urine testing should be timed according to the earliest and latest possible dates one is expected to ovulate.
Urine testing for LH surge should begin at least 2 days before the expected day of ovulation and continue until the LH surge or through day Once an LH surge is documented, it is no longer necessary to continue testing during that cycle. Periods may become irregular or absent. In this article, we look at symptoms and treatments options. Learn more. What does the LH surge mean for pregnancy? Medically reviewed by Holly Ernst, P.
Overview Duration When to test How to test Takeaway We include products we think are useful for our readers. What does a surge in LH mean? Share on Pinterest The period of fertility is short, so it is important to keep track of it.
How long does the LH surge last? When to test LH levels. Best ways to test LH levels. Share on Pinterest One of the best ways to test for the LH surge is to get a blood test.
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