This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Normal Menstruation, Abnormal Menstruation, Menopausal Physiology and forsight of conception, Subject name: Gynaecology & Obstetrics
Which of these is the function of Decidua basalis of the endometrium? 
Select and explain. 
A. Monthly proliferation in response to estrogen, B. Regeneration of endometrium, C. Shedding during menstrual phase, D. Secretory changes in response to progesterone
B: Regeneration of endometrium
Answer: B: Regeneration of endometrium 
Explanation: The superficial two thirds of endometrium is known as decidua functionalis. This layer undergoes monthly proliferative changes (in follicular phase) in response to estrogen and secretory changes (in secretory phase) in response to progesterone. Lower one third of endometrium, known as decidua basalis, does not undergo significant monthly proliferation, but instead is the source of endometrial regeneration after each menses.