Endometrium the body with human chorionic gonadotropin (HCG). HCG provides continued feedback throughout pregnancy by maintaining the corpus luteum, which will continue its role of releasing progesterone and estrogen. The endometrial lining is either reabsorbed (estrous cycle) or shed (menstrual cycle). In the latter case, the process of shedding involves the breaking down of the lining, the tearing of small connective blood vessels, and the loss of the tissue and blood that had constituted it through the vagina. The entire process occurs over a period of several days. Menstruation may be accompanied by a series of uterine contractions; these help expel
Menstrual cycle may be taken continuously, although this increases the risk of breakthrough bleeding. Breastfeeding causes negative feedback to occur on pulse secretion of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH). Depending on the strength of the negative feedback, breastfeeding women may experience complete suppression of follicular development, but no ovulation, or normal menstrual cycle may resume. Suppression of ovulation is more likely when suckling occurs more frequently. The production of prolactin in response to suckling is important to maintaining lactational amenorrhea. On average, women who are fully breastfeeding whose infants suckle frequently experience a return of menstruation at fourteen and a