Question

Explain the following phases in the menstrual cycle of a human female :
(i)Menstrual phase
(ii)Follicular phase
(iii)Luteal phase

Answer 1

(i) Menstrual phase: It extends from 1${}^{st}$ to 4${}^{th}$ day of the cycle. It occurs in the absence of fertilization. During this phase bleeding occurs as the endometrium of uterus is sloughed off. Menstrual flow consists of secretion of endometrial glands, cell debris, unfertilized ovum. After 4${}^{th}$ day, once again the FSH secretion from the pituitary is resumed and the new follicle starts developing.

(ii) Follicular phase: When the ovary is in this phase, uterus enters in proliferative phase. This takes place from 5${}^{th}$ to 13${}^{th}$ day of the cycle. During this phase new primordial follicle in the ovary develops due to the action of FSH from pituitary. It gradually changes into graafian follicle and production of estrogen starts. Only one follicle develops in one cycle.Corresponding to the changes in the ovary, uterus also undergoes proliferation. Endometrial glands, stimulated by estrogen do repair process of uterus.

(iii) Luteal phase: It corresponds with the secretory phase in uterus. It takes place between 15${}^{th}$ to 28${}^{th}$ day of the cycle.

Ovarian changes : In the ovary, corpus luteum is formed from empty graafian follicle. Progesterone is secreted now. If ovum is fertilized, corpus luteum is retained. LH and LTH from pituitary help in the maintenance of corpus luteum. If ovum is not fertilized, corpus luteum degenerates and forms corpus albicans.