Question

What are the 3 main phases in the menstrual cycle?

Answer 1

In fact, there are 4 phases of human female menstrual cycle which happens one after another but as you have mentioned `3` main so I will go with:

• Follicular phase or proliferative phase
• Luteal or secretory phase
• Menstrual phase

(One being skipped i.e ovulation phase)

Explanation:

Follicular Phase or Proliferative phase:

• Anterior lobe of pituitary gland releases `FSH`(follicle stimulating hormone) at the start of puberty.
• This hormone stimulates the development of several primary follicles.
• Only one of these follicles continue to grow with its primary oocyte.

• The remaining follicles break down by degenerative process called follicle atresia.

• FSH stimulates the ovary to produce estrogen hormone.

• Estrogen stimulates the endometrium(tissue lining inner wall of uterus) and vascularizes it.

• High level of estrogen inhibits the secretion of FSH from pituitary gland.

{Decrease of FSH and increase of estrogen stimulates the pituitary gland to secrete luteinising hormone`(LH)` which induces ovulation i.e discharge of ovum from follicle. This is known as ovulation phase. Mentioned it! Because otherwise it would be bit tricky to understand the topic}

Luteal phase or Secretory Phase:

• The follicle cells ruptured in follicle atresia form a special structure called corpus luteum. It is a yellowish grandular structure.
• Corpus luteum starts secreting progesterone.
• Progesterone further develops the endometrium and make it receptive for the implantation of zygote. Now if the fertilization occurs then the implantation of zygote take place . And if it does not occur then last phase of female reproductive cycle starts i.e mensturation.

Menstural Phase:

• In this phase, corpus luteum starts degenerating and thus secretion if progesterone is also reduced.

• Now endometrium has no supporting effect of progesterone. Consequently endometrium starts to breakdown.

• This starts the discharge of cell debris and blood through vagina which is known as menstruation.

Hope it helps...