Estrogen is secreted during pregnancy, mostly by-
**Core Concept**
During pregnancy, estrogen levels surge to support fetal development, particularly the growth of the uterus, placenta, and breasts. Estrogen is synthesized from androgens by the action of the enzyme aromatase.
**Why the Correct Answer is Right**
Estrogen is primarily produced in the placenta, which is a unique endocrine organ that develops in the uterus during pregnancy. The placenta produces human chorionic gonadotropin (hCG), which stimulates the corpus luteum to secrete progesterone. The placenta also produces estrogen through the action of aromatase, which converts androgens into estrogens. This estrogen is essential for maintaining a healthy pregnancy, promoting fetal growth, and preparing the mother's body for childbirth.
**Why Each Wrong Option is Incorrect**
**Option A:** The ovaries do produce estrogen, but not in the quantities seen during pregnancy. The ovaries are responsible for estrogen production during the menstrual cycle.
**Option B:** The adrenal glands do produce some androgens, which can be converted to estrogens, but they are not the primary source of estrogen during pregnancy.
**Option C:** The testes produce testosterone, which is an androgen that can be converted to estrogen, but they are not responsible for estrogen production during pregnancy.
**Clinical Pearl / High-Yield Fact**
The placenta produces over 200 different proteins, hormones, and other substances during pregnancy, making it a highly active endocrine organ.
**Correct Answer: C. The placenta**