BIOL 155 Lecture Notes - Lecture 20: Spiral Artery, Corpus Luteum, Endocrine System
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Ubc biol 155 lecture 18 notes reproductive system. The functional layer of the endometrium undergoes physical changes throughout the ovarian cycle and these changes are controlled by ovarian hormones. The most obvious change occurs during the menstrual phase, which is triggered by the end of the luteal phase in the ovary. Progesterone levels drop rapidly as the corpus luteum degrades. This drop causes the arteries which serve the functional layer of the endometrium (the spiral arteries) to constrict, cutting off the blood flow to the functional layer. Soon after, the functional layer becomes necrotic and is sloughed off, passing out through the cervix and vagina. During this period, the smooth muscle of the uterus can become irritable and often undergo spontaneous contractions. The contractions (which can be felt as cramps) serve to facilitate sloughing of the necrotic tissue. Once the previous functional layer has been sloughed, the uterine lining begins to proliferate.
