Progesterone is secreted by the _____.

• A. Follicles
• B. Corpus Luteum
• C. Endometrium
• D. Ovarian Stroma

Answer: (B)

Progesterone is secreted by the corpus luteum. After ovulation, the ruptured follicle becomes the corpus luteum, and its luteal cells produce progesterone under LH stimulation. This hormone transforms the endometrium into a secretory state, preparing it for possible implantation and helping sustain early pregnancy. If fertilization doesn’t occur, the corpus luteum regresses and progesterone levels fall, leading to menses. The other structures aren’t the primary sources: the mature follicle mainly makes estrogen; the endometrium responds to progesterone rather than producing it; the ovarian stroma doesn’t secrete significant progesterone. During pregnancy, the placenta eventually takes over progesterone production, but the question focuses on the typical luteal-phase source.