Menstruation is the cyclic, orderly slowing of the uterine lining in response to the interactions of hormones produced by the hypothalamus, pituitary, and the ovaries. It is normally known to be the number of days between the first day of the menstrual bleeding of one cycle to the onset of menses of the next cycle is expected to be about twenty-eight days. However, it can vary anywhere between twenty-one to thirty-five days. It varies from cycle to cycle, and regular cycles may sometimes be ovulatory or anovulatory. The luteal phase of the cycles are relatively constant in all women with a duration of fourteen days. Two significant occurrences. ·       First, only a single ovum is normally released from the ovaries each month so that, normally, only a single foetus will begin to grow at a time. ·       Second, the uterine endometrium is prepared in advance for implantation of the fertilized ovum at the required time of the month. What are the hormones of the female genital tract? Consists of three hierarchies of hormones at the hypothalamic releasing hormone from the hypothalamus known as gonadotropin releasing hormone or GnRH. ·       From the pituitary, the anterior pituitary sex hormones, that is follicular stimulating hormone ·       FSH, and luteinizing hormone, both of which are secreted in response to the release of gonadotropin releasing hormone from the hypothalamus. ·       Lastly, the ovarian hormones, estrogen and progesterone, which are secreted by the ovaries in response to the two female sex hormones from the anterior pituitary gland. Here is a diagrammatic representation, and we will see many such pictures in future of the follicular stimulating hormone and the luteinizing hormone. Note that the follicular stimulating hormone is very predominant in the first half of the cycle and is known to be active in stimulating the follicular growth. The luteinizing hormone, however, is very low in the initial part, but then is known to trigger the ovulation in mid cycle. The follicles tend to grow right from the beginning of the second or third day of the menstruation and then reaches its peak around mid-cycle when the LH trigger helps for the ovulation and then becomes a corpus luteum and helps to nurture the young pregnancy in the womb. We have the ovarian cycle follicular phase and the luteal phase, the endometrium in the proliferator phase, and the secretory phase. Ovulation occurs about 10-12 hours after the LH peak and 36 hours after the Easter day old peak. The most reliable indicator for the timing of ovulation is the onset of the LH surge, which begins 36 hours before ovulation. Coming to the luteal phase, the luteinization, as it's called, the granulosa cells get luteinized and now start producing both estrogen and progesterone and, therefore, corpus luteum formation. The lifespan of the corpus luteum is fixed around fourteen days. At the end of the luteal phase, the corpus luteum undergoes luteal lysis unless rescued by the HCG from the implanting embryo. Every month, the uterus prepares for a pregnancy, which if does not occur, menses starts. Menstruation is sometimes described as weeping of a disappointed uterus for a baby. Three functional layers- the stratum basalis, stratum spongiosum, and stratum compactum. Menses is the shedding of the top two layers caused by the fall in progesterone and estrogen levels due to the degeneration of the corpus luteum. Proliferative phase of the endometrial cycle The menses stops, then regeneration of epithelium from the basalis layer starts. Ovarian follicular phase corresponds to proliferative phase. Estrogen from the gradual cell of the follicles causes the regeneration of the endometrium. The endometrium can grow from point 3-5 mm by the time of ovulation. Withdrawal of the FSH from the less developed follicles leads to atresia. The increasing estrogen levels is thought to trigger a marked increase in secretion of LH, which triggers ovulation and the formation of the corpus luteum. The corpus luteum secretes large quantities of progesterone and estrogen, which have a negative feedback on the FSH and LH, and, hence, a decrease in their levels. If you looked at the days of one to four, the ovarian events related to the individual events and the hormonal dynamics between the first and four days, you'll see a recruitment cohort of follicles, and they start growing when the individual lining sloughs.   Hormonal dynamics would be that estrogen and progesterone are low. FSH and LH are released from the inhibition. But as we go across to the day five to seven, the selection process occurs in the ovary with a single follicle, which is destined to ovulate and no surrogate follicle. But at the same time, in the endometrium, the proliferation has started, and the plasma estrogen rises because of secretion from the select dominant follicle. But as we go to the eighth to twelfth day, the dominance has already occurred, and atresia of all follicles except the dominant follicle, and the dominant follicle thrives uniquely despite that suppressive milieu. But in the endometrium, increased estrogen will stimulate the growth of the gland and the stroma, and therefore, the hormones will increase estrogen and inhibit will inhibit the FSH. What happens now between 13-15th day, the ovulation occurs, which is mediated by the FSH follicular enzymes and prostaglandins. Oocyte is induced to complete its first meiotic division. At the endometrial cycle, the transition from the proliferative to the secretory endometrium starts. At the hormonal level, the LH surge induced by high plasma estrogen, and that is the positive feedback. But beyond the fifteenth to the twenty fifth day, the corpus luteum forms. The secretory endometrium develops on the endometrium and with the hormone progesterone and estrogen are secreted and the FSH LH secretions are inhibited, so no new follicle develops. As we go up to the twenty fifth to twenty eighth day, luteolysis occurs, corpus luteum degenerates, recruitment of new ovarian follicles for the next cycle begins, and in the endometrium, it begins to slough due to the withdrawal of the progesterone support. The window of endometrial receptivity is restricted to days 20-24 of a 20-28 days cycle. The receptivity is heralded by the progesterone induced formation of pinopods. Pinopods are specific surface epithelial cells that lose their microvilli and develop smooth protrusions, appearing and regressing during the window of receptivity. The pinopods may serve to absorb fluid from the uterine cavity, forcing the blastocyst to be in contact with the endometrial epithelium. Blastocysts prefer to attach at sites with pinopods. Pinopods appear around day 21 and are present only for a few days during implantation. This blog is just the surface on the ocean. This topic is much deeper. If you are interested to learn more, join the Fellowship in Reproductive Medicine offered by Medline Academics. Medline Academics is derived from the educational background and the advancement of reproductive healthcare sector that Dr. Kamini Rao has developed. It offers complete e-learning solutions or certification in relative course of study in other a specialized division of medical science like reproductive medicine, embryology and healthcare management and the like. In particular, Medline Academics utilizes technology, and provides students with Fellowship in Reproductive Medicine in India from the best instructors from around the globe; thus, it seeks to ensure that healthcare providers are aware of latest advances in their fields. Dr. Kamini Rao Hospitals are specialized in reproductive care, especially infertility treatments and women’s health. These hospitals are provided with modern technological facilities related to reproductive health and the best procedure like IVF, IUI, and advanced gynaecological services. Standing out for the patient-tailored approach and the physician-centred team of professionals, headed by Dr. Kamini Rao Hospitals offer high success rates of fertility treatments and a human touch in women’s health problems.