Physiology of Menstruation PDF

Prepared by Prof. dr Hanan Elsayed Cyclic uterine bleeding caused by shedding of endometrium. It occurs between menarche (first menstrual cycle) and menopause (physiological cessation of menstruation).  Age at menarche: 10:16 years with an average of 13 years. Duration of blood flow: 2:7 da...

Prepared by Prof. dr Hanan Elsayed Cyclic uterine bleeding caused by shedding of endometrium. It occurs between menarche (first menstrual cycle) and menopause (physiological cessation of menstruation).  Age at menarche: 10:16 years with an average of 13 years. Duration of blood flow: 2:7 days. Length of menstrual cycle: 28+7 days. Estimated from the first day of menstruation to the first day of the next period. Amount of menstrual blood: 30:60 ml, during the whole period. The woman is usually uses 3 pads daily. If the amount of menstrual blood exceeds 80 ml it is considered to be abnormal and is known as menorrhagia.  Normally the menstrual blood does not coagulate  The menstrual cycle is composed of two cycles, ovarian cycle and endometrial or uterine cycle. Both cycles occurs simultaneously  This cycle describes the changes of the ovaries and can be further divided into 3 phases. I. Follicular phase: during the first half of the menstrual cycle, the anterior pituitary secretes both FSH and LH. The FSH stimulates the growth of several primary follicles in both ovaries (100-1000). However, only one follicle reaches maturity and forms a graafian follicle which secretes increasing amount of estrogen. The estrogen level reaches a peak about 48 hours before ovulation (day 12). This estrogen peak stimulates increased secretion LH which reaches a peak about 24 hours before ovulation (day 13). The LH peak leads to ovulation (day 14) and corpus luteum formation - During this phase the LH maintains the growth of the corpus luteum and stimulates it to secrete estrogen and progesterone. - The corpus luteum has a limited life span (14+2 days) after which it degenerates. This leads to a drop in the level of estrogen and progesterone causing separation of the endometrium and menstruation. - Also the drop in the level of these hormones stimulates the hypothalamus to secrete more GnRH and thus a new cycle is started in. This cycle describes the changes which occur in the endometrium every month and also it can be further divided into 3 phases: I. Menstrual phase About 1:5 days and during which the superficial functional layer of the endometrium separates leaving the basal layer to allow regeneration of the endometrium  Begins with the start of menstruation and ends at the time of ovulation, Under the effect of estrogen, the endometrial thickness reaches 3-4 mm, Vascularity is increased. Secretory or postovulatory phase begins at ovulation and ends at the onset of menstruation, under the effect of estrogen and progesterone, the endometrial thickness reaches 6-8 mm, vascularity is increased greatly.  If pregnancy does not occur ,the corpus luteum degenerates at the day 22-24 of the cycle thus secretion of estrogen and progesterone will stop and leads to break down and shedding of the lining (endometrium) , called menstruation.  If pregnancy occurs, the corpus luteum continues to develop and become corpus luteum of pregnancy and function till the 4th month of pregnancy, where the placenta takes its function. The ovary will not select another follicle for ripening and no menstrual cycle will occur.