The Menstrual Cycle

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THE MENSTRUAL CYCLE According to the Ross & Wilson (2002) the menstrual cycle is defined as the series of events which regularly occurs in females throughout the childbearing period. In this cycle notable changes take place in the ovaries and in the walls of the uterus. Prior to discussing the menstrual cycle it would be beneficial to have a brief overview of internal organs of female reproductive system. The internal organ consists of mainly vagina, fallopian tube, ovaries and uterus. The vagina acts as a passage from vulva to the uterus. The lining of the vaginal walls always remain moist and this moisture is a kind of acidic in nature which acts as a barrier to infection. The uterus has three parts the body, the fundus and the cervix. The uterine wall is consists of three layers especially perimetrium, myometrium and endometrium. The myometrium helps the uterus to contract during the childbirth whereas the endometrium widens during the menstrual cycle and also helps in implantation of the fertilized ovum. There is fallopian tube attached to the uterus and approximated size is 10 cm. At the end of each fallopian tube there is finger like structure called fimbriae. The surface of the ovaries wrinkles as the ova is released. There are innumerable numbers of immature follicle at birth and each of these follicles contains oocyte. Ovaries are female gonads or glands and meiosis is the process by which the oocyte gets divided. The primary oocyte has 46 chromosomes and the secondary oocyte contains 23 pairs chromosomes. Hypothalamus secretes the Lutenising Hormone Releasing Hormone (LHRH) which stimulates Anterior Pituitary to secrete Follicle Stimulating Hormone and Luteinising Hormone as well. Follicle Stimulating Hormone helps in formation of ovum. Babycentre (2008) states that the whole process starts in the brain. The hypothalamus produces gonadotrophin-releasing hormone (GnRh), which travels to the pituitary gland and signals it to release follicle-stimulating hormone (FSH).So he hormones which are closely associated with menstrual

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cycle is: Gonadotropin Releasing Hormone (GnRH), Follicle Stimulating Hormone (FSH), Lutenising Hormone (LH), Oestrogen and Progesterone. Stuart (1990) states that the cyclic changes in the secretion of gonadotropic hormones from the anterior pituitary cause the changes observed in the ovaries during a menstrual cycle. There are many follicles which get enlarged but only one gets the maturity in each month. When the follicle gets completely enlarged then it secrets the hormone called Oestrogen. During ovulation the Graafian follicle bursts and releases ovum into the fallopian tube. In turns this ruptured Graafian Follicle becomes glandular in shape and this is called Corpus Luteum.

This Corpus Luteum helps in secreting

Progesterone and Oestrogen. According to Ross & Wilson (2002) the menstrual cycle is divided into three phases: •

Menstrual Phase

•

Proliferative Phase

•

Secretive Phase

Menstrual Phase:

In case of unfertilized ova the Corpus Luteum starts

degenerating but in case of fertilized ovum its get support by Human Chorionic Gonadotrophin Hormone. In this phase the progesterone and oestrogen

level

gradually declines Endometrial

lining get shed for

menstruation. The secretions from the endometrial glands, endometrial cells, blood from the broken down capillaries and unfertilized ovum all these are closely associated with the menstrual flow. After degeneration of the Corpus Luteum the declined level of oestrogen and progesterone lead to resumption of secretion and thus the level of Follicle Stimulating Hormone rise for next cycle. Proliferative Phase: In this phase the maturity of ovarian follicle takes place and the layers of the endometrium get well prepared to receive fertilized ovum. The walls of the endometrium become gradually.

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The proliferative phase ends after ovulation and when the production of the progesterone declines. Secretory Phase: As soon as the ovulation gets completed the lining of the ovarian follicle gets stimulated by the Lutenising Hormone. This Lutenising Hormone helps in producing the Corpus Luteum. Because of progesterone the endometrium becomes thick and secretory glands produce watery mucus and this watery mucus helps for the passage of spermatozoa. A cycle begins on the first day of bleeding and continues up to, but not including, the first day of the next period. Women’s cycles range from 21 to 40 days or more, with an average of around 28 days. The length of a woman’s cycle may change a little or a lot from month to month. Its the cycle of around 28 days hence the following changes occur in each stage: Day 1: The onset of each menstrual cycle. Day 1-5: The layers of endometrium get shed and thereby menstrual flow occurs. Day5-14: The maturing follicle in the ovary helps in releasing Oestrogen and this oestrogen has the triple function as it controls the secretion of Gonadotropin Hormone, helps in triggering Follicle Stimulating Hormone and thickens the endometrial walls of uterine. Day 14: Graafian gets ruptured by the Luteinising Hormone. Day 14-16: The follicles which are empty form Corpus Luteum for production of more oestrogen and progesterone and fertilization takes place during this day. Day 17-20: Ovum travels down to the fallopian tube to enter the uterus for growth. If fertilisation does not occur, the follicle starts to break down and slowly stops producing hormones. When the follicle has broken down completely and is no longer releasing any hormones, the womb sheds its lining. This is your period. And so begins your next cycle.

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References: Anne W, Allison G (2002) Ross & Wilson Anatomy and Physiology in Health and Illness, 9th Ed, London: Churchill Livingstone, Edinburgh, p.445 Babycentre 2008 (London) available on www.babycentre.co.uk accessed on May 19th 2008. Stuart I.F (1990) Human Physiology, 3rd Ed. Wm.C.Brown Publisher, USA; p. 667

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