corpus luteum

the tissue that forms within the ovary after a Graafian follicle (the structure that contains the egg) ruptures and releases an ovum at the time of OVULATION . It consists of a mass of cells containing yellow, fatty substances and secretes the hormone PROGESTERONE , which prepares the womb to receive a fertilized egg. If the egg is not fertilized and no implantation of an embryo takes place, the corpus luteum degenerates. However, if a pregnancy ensues, the corpus luteum expands and secretes progesterone until this function is taken over by the placenta at the fourth month.