Phases of Menstrual Cycle - Reproduction
Four phases of the menstrual cycle are usually distinguished: the menstrual, proliferative (follicular), ovulatory and progestational (luteal). The proliferative phase is conditioned by estrogen and extends from the end of menstruation to ovulation. Ovulation occurs near the middle of the cycle. At the end of menstrual disintegration, the endometrium is thin and poorly vascularised and only the basal parts of the endometrial glands remain. The endometrium thickens as the estrogen titers rise and the glandular and vascular patterns are restored. No conspicuous changes occur in the endometrium during the ovulatory process.
Cyclic variation in the body temperature of the human female correlate with menstrual changes. A distinct rise in basal body temperature occurs at ovulation and remains high until the onset of the next menstrual period. The changing titers of hormones during the menstrual cycle apparently account for the temperature fluctuations. During the progestational phase the uterus is under the influence of both estrogens and progestogens and the endometrium differentiates into a tissue that can fulfil the requirements of an embryo ready to implant. The progestational endometrium normally requires both estrogens and progesterone. it is the only type of structure in which blastocyst can readily implant and develop normally. If implantation has not occurred the corpus luteum diminishes in function and degenerative changes are observable in the endometrium. With menstruation the outer portion of the endometrium is lost and there is bleeding into the uterine cavity.