Question

Describe the changes in the ovary and the uterus as induced by the changes in the level of pituitary and ovarian hormones during menstrual cycle in a human female.

Hint:

Think of FSH and LH acting on the ovary, causing estrogen and progesterone release. Estrogen builds the uterine lining, and progesterone maintains it. If no pregnancy, hormones drop, and the lining sheds.

Answer 1

The menstrual cycle, approximately 28 days long, is regulated by the interplay of pituitary and ovarian hormones, leading to cyclical changes in the ovary and uterus:

1. Follicular Phase (Ovary) / Menstrual and Proliferative Phase (Uterus):

• Pituitary Hormones: FSH stimulates follicular development in the ovary.
• Ovarian Hormones: Developing follicles produce increasing levels of estrogen.
• Ovary Changes: Primary follicles mature into Graafian follicles.
• Uterus Changes: Low hormone levels cause menstruation (shedding of the endometrium). Estrogen then promotes the proliferation and thickening of the endometrium.

2. Ovulatory Phase (Ovary) / End of Proliferative Phase (Uterus):

• Pituitary Hormones: A surge in LH triggers ovulation.
• Ovary Changes: Release of the ovum from the Graafian follicle.
• Uterus Changes: Endometrium continues to thicken due to estrogen.

3. Luteal Phase (Ovary) / Secretory Phase (Uterus):

• Pituitary Hormones: LH maintains the corpus luteum.
• Ovarian Hormones: Corpus luteum secretes progesterone and estrogen.
• Ovary Changes: Formation and maintenance (or degeneration) of the corpus luteum.
• Uterus Changes: Progesterone promotes the secretory phase of the endometrium, making it receptive for implantation. If no fertilization occurs, the corpus luteum degenerates, hormone levels drop, and menstruation begins again.