BIOL 155 Lecture Notes - Lecture 23: Adrenal Cortex, Reproductive System, Fetus
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Ubc biol 155 lecture 21 notes reproductive system. Parturition the action of giving birth to young; childbirth. Childbirth is culmination of pregnancy; also called labour. Parturition refers to giving birth while labour refers to the series of events that expel the infant from the uterus, i. e. the events that cause parturition. The precise mechanism that initiates labour is not known. Several events and three hormones seem to be involved in the process. There is a shift from progesterone to estrogen dominance. During the last few weeks of pregnancy, estrogen levels reach their highest value, which may be due to stimulation of the placenta by adrenocortical hormones released from the fetus. The very high estrogen levels stimulate the uterine muscle cells to produce abundant receptors for a hormone oxytocin. This antagonizes the effect of progesterone on the uterus and the myometrium becomes irritable and begins to contract.
