This period is marked by a characteristic event repeated almost every month (28 days with minor variation) in the form of a menstrual flow (i.e. shedding of the endometrium of the uterus with bleeding). It may be temporarily stopped only by pregnancy.
i. Menstrual cycle is controlled by FSH, LH, estrogen and progesterone.
ii. 1st Menses is called menarche while the onset of menses and development of secondary sexual character is called puberty, usually at age of 13. If puberty starts early then known as precocious puberty. Earliest known is in a 6 year old child.
iii. Dysmenorrhoea is painful menses.
iv. Amenorrhoea is non-occurrence of menses and oligomenorrhea is irregularity of menstrual cycle.
v. Menopause is stopping of ovulation and menses. Average age 51 years. Post menopausal effects include hot flashes, irritability, fatigue, anxiety, decreased strength of bones, etc.
The period of a mentrual cycle is counted from the day of the onset of the flow to the next onset after 28 days. This period can be divided into four main phases.
It lasts for 3-5 days during which blood is discharged out. The bleeding is caused due to the shedding of the uterine lining rupturing the blood vessels which is mainly due to decrease of estrogen and progesterone secretion.
As the follicle grows it produces certain hormones which reactivate the uterine wall to become thickened and to be supplied with a lot of blood. The thickening of endometrium occurs under the influence of oestrogen hormone (secreted by granulosa cells of the follicle) in association with progesterone.
Due to priming effect of oestrogen on progesterone receptors, both hormones stimulate the growth and secretory activity of endometrial glands, so that they curl like a helix. This change is kind of preparation of the uterus to receive the fertilized egg and to provide for the development of the future embryo.
During this phase production of FSH decreases while that of LH increases which leads to ovulation on about the 14th day. The follicle ruptures and the released egg travels down the oviduct. This phase helps in fertilization in the following ways, like –
i. Uterine movements help in spread of sperms in female reproductive tract.
ii. Ciliary movements in the epithelium of fallopian tubes for bringing in the ovum.
It lasts from 15-28 days. Uterus lining thickens further and becomes secretory. This stage is meant for receiving the fertilized ovum (implantation). Emptied follicle in the ovary turns into corpus luteum and supervised by LH of anterior pituitary.
If there is no fertilization the egg disintegrates (because the level of estradiol and progesterone switches off both gonadotropins) and the uterine lining restarts shedding on the 28th day. The shedding occurs when the corpus luteum regresses and hormonal support for the endometrium is withdrawn.
The endometrium becomes thinner which adds to the coiling of the spiral arteries. These coiled and constricted spiral arteries supply the upper two thirds of the functional endometrium. Foci of necrosis appear in endometrium and these coalsce (means come together in one body or mass).
There is an additional spasm and then necrosis of the walls of the spiral arteries, leading to spotty haemorrhages that become confluent and produce the menstrual flow. If, on the other hand, the egg is fertilized, it gets implanted or fixed into the uterine wall with no menstrual discharge. This is because the level of progesterone hormone, secreted by the persistent corpus luteum, is increased. This hormone prevents maturation of another follicle.