Corpus Luteum

Following ovulation, the remnants of the follicle in the ovary undergo rapid changes. The space occupied by the follicular fluid fills with blood that soon clots, and the follicular cells enlarge greatly to form a new glandular structure within the ovary, called the "corpus luteum." When the corpus luteum ceases to function, the concentrations of estrogen and progesterone (hormones) decline rapidly, and in response, blood vessels in the endometrium (uterine lining) become constricted and soon disintegrate and slough away. At the same time, blood escapes from damaged capillaries, creating a flow of blood and cellular debris that passes through the vagina as the menstrual flow. The beginning of the menstrual flow marks the end of a menstrual cycle and the beginning of a new cycle.