Thu. Jun 1st, 2023
Human menstrual cycle

Human menstrual cycle

The mention cycle is the regular changes and the activity of the ovaries and endometrium that take place in a human female from the age of 11 to 50 years every month and is responsible for making the reproduction in human beings. The endometrium is a layer of the tissue lining inside of the uterus of a female. This lining consist of the functional layers which is subject to hormonal changes and during the menstruation and a thin Basal layer which is responsible for feeding the over lining functional layer. This menstrual cycle actually consist of two interconnected and synchronised processes.

1) The ovarian cycle :- The ovarian cycle which centres on the development of the ovarian follicles and ovulation.

2) The utarian cycle or the endometrial cycle :- The utarian or the endometrial cycle with centres on the way in which the functional endocrine thickness and shares in response to the ovarian activity.

Menarche is referred to the onset on the first menstrual period usually occurs during the early adolescence as a part of puberty by the age of 10 to 13. Following menarche the menstrual cycle rickers on a monthly basis pausing only during the pregnancy period, until a woman reaches menopause that because by this age her ovarian function decliness of having menstrual periods. The monthly menstrual cycle can varies in duration from 20 to 35 days with an average of 28 days. Each menstrual cycle begins at the first day of menstruation and which is referred to as the day one of the cycle. Ovulation on the release of the oocytes from the ovary usually occurs 14 days before the first day of menstruation. So for an average 28 days Menstrual cycle The meaning of which is that there are only 14 days leading up to ovulation and the 14 days following ovulation that is the postovulatory phase.

During the two phases as stated above the ovaries and the endocrine both undergo their own set of changes which are separate but related as a result each phase on the menstrual cycle for the two different names describe these different parallel processes. For the ovaries 2 weeks leading up to ovulation is called ovarian follicular phase which responses to the menstrual and the proliferative phases of the endometrium. Similarly the following 2 weeks of the ovulation is referred to as the ovarian luteal phase which also corresponds to the secretory phase of the endometrium.

2) The ovarian follicular phase:- This process starts on the first day of the Menstrual cycle and lasts upto week 1 and 2 of a 4 weeks cycle. The whole menstrual cycle is controlled by the hypothalamus gland and the pituitary gland which are like the mastermind of the process of reproduction. The hypothylamus is a part of the brain that secretes Gandotropin-releasing hormone or GnRH this causes for the nearby interior pituitary gland to release follicle stimulating hormone and luteinizing hormone. Before Gandotropin-releasing hormone is released at a steady rate but once the puberty hits the Gandotropin-releasing hormone is released in excess sometimes and sometimes it is released less. The frequency and magnitude of the Gandotropin-releasing hormone pulses determine how much follicles stimulating hormone and luteinizing hormone will be produced by the pituitary gland.

These two hormone controls the Menstruation and ovarian follicles each of which is initially made up of immature sex cells are the primary oocyte surrounded by layers of the theca and granuloma cell the hormone-secreting cells inside the ovary. Over the course of the follicular phase these oocyte-containing groups of cells or follicles grow on and complete for a change at ovulation. During the first 10 days of the process the theca cells develop receptors and one luteinizing hormone In response secrete large amount of the androstenedione hormone and androgen hormone.

Similarly granny solar cells develop receptors and bind the follicle stimulating hormone in response to which it produces the enzyme Aromatase. Aromatase converts this androstenedione secreted from the theca cells into 17 beta-estrodiol which fall under the category of the estrogen family. During the days 10 through 14 of this face granulosa cells also begin to develop liberalism hormone effects in addition to the follicles stimulating hormone receptors which are already present there .

As the follicle group an estrogen is released into the bloodstream the increased Estrogen Level act as a negative signal telling the pituitary to secrete the follicle stimulating hormone. As a result on the decrease in the level of the follicle stimulating hormone production some of the developing follicles in the ovary will stop growing regress and die. The follicles that has the most follicle simulating hormone receptor will hereby continue to grow becoming a dominant follicle that will eventually undergo the process of ovulation.

This dominant follicle continues to secrete estrogen hormone and the rising estrogen levels make the pituitary more responsive to the pulsatile action of Gandotropin-releasing hormone from the hypothylamus gland. As blood estrogen levels starts to steadily climb higher and higher the estrogen from dominant follicle now gives a positive signal that makes it secrete a whole lot of follicle stimulating hormone and luteinizing hormone in response along with the Gandotropin-releasing hormone. This search for the follicle stimulating hormone andar luteinizing hormone usually happens 1 or 2 days before ovulation and is responsible first imlating the rupture of the ovarian molecule and release of the oocyte. That is for the most of the follicular phase the pituitary gland which saves it’s energy then when it senses that the dominant follicle is ready to release, the pituitary gland uses all its energy needed to secrete enough follicle stimulating hormones and luteinizing hormone to induce ovulation during the process.

While the ovary is busy preparing an egg for ovulation inside the uterus meanwhile the hormones are preparing the endometrium for implantation and maintenance of pregnancy. This process begins with the menstrual phase which come to an end with the old endometrial lining or the functional layer from the previous cycle been shed and eliminated through the vagina producing the bleeding which is known as the menstrual period in the common language. The menstral phase last upto to an average of 5 days and is followed by the proliferative phase during which the Estrogen Level stimulates thickening of the endometrium growth of the endometrial glands and this leads to the emergence of Parul arteries which grows a little under the influence of estrogen from the Basil layer to feed the growing functional endometrium. Rising estrogen levels also helps change the consistency of the cervical mucus making it more hospitable to incoming sperms. The combined effect of this spike in estrogen on the uterus and cervix help to optimise the chance off fertilization which reaches the highest possibility during between 11th and 15th of an average 28 days Menstrual

Following ovulation the remainant on the ovarian follicle which becomes the Corpus luteum. This Corpus luteum is made up of luteinized theca cells and the luteinized granulosa cells which means that these cells have been exposed to the follicle stimulating hormone level that occur just before the process of ovulation. Luteinized theca cells keep secreting androstenedione and the luteinized granulosa which keeps on converting into 17 beta-estrodiol as before. However luteinized granulosa also responses to the luteinizing hormone concentration that are present after ovulation by increasing the activity on the cholesterol site chain cleavage enzyme or P450scc for short. This enzyme helps in converting more cholesterol pregnenolone into a progesterone precursor. So the luteinized granulosa secretes more progesterone than estrogen during the luteal phase. Progesterone gives a negative signal on the pituitary gland resulting in the decrease in the release on the follicle stimulating hormone and lieutenazing hormone. At the same time luteinized granulosa cells are beginning to secrete inhibin which similarly inhabits the pituitary gland form making more of the follicle stimulating hormone.

Both of these processes result in the decrease in the level of the Estrogen which means that the progestron becomes more dominant hormone present during this phase of the cycle. Together with the decrease level of the estrogen and the rising level of progesterone it makes signals to the ovulation has occurred enhance make the endometrium acceptive to the implantation of the fertilization gamete.

Under the influence on the progesterone the uterus enters into the secretory phase of the endometrial cycle. While this time the aspirral arteries grow the most and become coiled the uterine glands become to secrete mucus. After 15 days of the cycle the optimal Window for the fertilization begins to close. Cervical mucus tights to thicken and become less hospitable to the sperms. Overtime the Corpus luteum gradually degenerates into the non functional Corpus albicans. Tha Corpus albicans doesn’t make hormone so student and progesterone level slowly decreases. When progesterone reaches its lowest level the spiral arteries collapse and the functional layer for the endometrial prepare to shade through menstruation. This shading makes the beginning of a new menstrual cycle and another opportunity for fertilization.

By Anrudh

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