Question

irculating progesterone decreases from day 22 to day 28.

(a) What events cause this decrease?

(b) How does the uterus respond to decreasing progesterone (and estrogens) after day 28?

Answer 1

A. ANSWER: Progesterone and estrogen attains the plateau at day 20 and initiates the negative feedback mechanism to decrease the secretion of these hormones. Also the corpus leutum which secretes progesterone will change into corpus albicans incase if the maturing egg is not fertilized. The corpus leutum can stay active for upto 2 weeks.

B. ANSWER: Progesterone is a pregnancy maintianing hormone. When the corpus leutum which secretes the hormone transforms into corpus albicans which does not secrete this hormone. Hence the uterus which is prepared for accomodating the fertilized egg will undergo changes. The main changes include the separation of stratum functionalis of the endometrial layer. It is the superficial layer which usually sloughs of if there is no fertilization. This causes bleeding of about 50 ml during the first 3 to 5 days in menstruation.