Question

Describe various phases of menstrual cycle emphasizing the role of hormones.

Answer 1

1. Menstrual Phase (3-5 days):

   • Shedding of the endometrium causing menstrual bleeding.
   • Triggered by the decrease of LH and progesterone due to degeneration of corpus luteum.
   • Estrogen levels also fall, causing breakdown of endometrial lining.

2. Proliferative Phase (6th to 13th day):

   • Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) gradually increase.
   • Development of a primary follicle to mature Graafian follicle in ovary.
   • Follicles secrete estrogen that stimulates regeneration and thickening (2-3 mm) of endometrium.
   • Endometrial glands become coiled, arterioles grow and vascularize the uterus lining.

3. Ovulatory Phase (around 14th day):

   • LH and FSH surge, especially LH surge triggers ovulation (release of secondary oocyte).
   • LH causes rupture of Graafian follicle to release the egg into the fallopian tube.

4. Secretory (Luteal) Phase (15th to 28th day):

   • Corpus luteum forms from ruptured follicle under LH influence.
   • Corpus luteum secretes progesterone and some estrogen.
   • Progesterone thickens and vascularizes endometrium, stimulating uterine glands to secrete nourishing mucus for fertilized egg.
   • Progesterone inhibits FSH and LH release to prevent development of new follicles.
   • If fertilization does not occur, corpus luteum degenerates, progesterone level falls, leading to endometrial breakdown and start of next menstrual phase.