Other placental mammals undergo a process where the uterus lining is reabsorbed into the body, a process sometimes called concealed ovulation. Apparently, our lining is too thick to be reabsorbed. Scientists are still not completely sure why some mammals menstruate and others do not. All foetuses will look for nourishment in the uterus ,but some go deeper into the uterus lining than others. In mammals like horses and pigs, the embryo sits on the surface of the uterus lining, whereas in primates, it moves deeper inside.
GCSE scientists – you need to be able to explain the stages of the menstrual cycle, and how hormones control it. For help with this, try our new guide “How to work with the Menstrual Cycle”. It includes a description of the stages, and how hormones interact to control it. As always there are questions to try, and answers to check understanding.
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