The corpus luteum and related hormone progesterone play crucial roles in the early developmental stages of a future human child. In a female human body, each month, following ovulation, a group of ovarian cells called the corpus luteum develops. It plays a crucial role in secreting progesterone. The anterior pituitary gland produces luteinizing hormone, which triggers formation of the corpus luteum. In addition, lesser amounts of progesterone are also produced by the ovaries, outside the corpus luteum, and the adrenal glands, as well as the placenta during pregnancy.
The main importance of the corpus luteum is in preparing the uterus to receive a fertilized egg, should fertilization occur. Progesterone is crucial for this stage of preparation for pregnancy. Progesterone stimulates the growth of the blood vessels that supply the endometrium, or the lining of the uterus. It also stimulates glands within the endometrium that will later generate and supply key nutrients to an embryo, if it should be successfully conceived and implanted.
If no embryo is conceived, then the corpus luteum will break down, causing a decrease in the production of progesterone. Without an embryo to support, the uterine lining will not be maintained by progesterone; it breaks away from the uterus and is released from the body as menstrual bleeding.