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
Pharmacokinetics of progesterone half-life of progesterone in the circulation is very short at a range of about 3 to 90 minutes. Previous studies using RIA have reported an overestimated half-life of oral progesterone of about 16 to 18 hours. A subsequent, reliable study using high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) reported a half-life of oral progesterone of about 4.6 to 5.2 hours when it was taken with food. Due to the short half-life and duration of action of oral progesterone, it is often taken in divided doses of two or three times per day. Because of studies that used RIA, it was incorrectly