<P> The endometrium is the inner epithelial layer , along with its mucous membrane , of the mammalian uterus . It has a basal layer and a functional layer ; the functional layer thickens and then is shed during menstruation in humans . Some other mammals including apes , Old World monkeys , some species of bat , and the elephant shrew menstruate . In most other mammals the endometrium is reabsorbed in the estrous cycle . During pregnancy , the glands and blood vessels in the endometrium further increase in size and number . Vascular spaces fuse and become interconnected , forming the placenta , which supplies oxygen and nutrition to the embryo and fetus . The speculated presence of an endometrial microbiota has been argued against . </P>
<P> The endometrium is the inner epithelial layer , along with its mucous membrane , of the mammalian uterus . It has a basal layer and a functional layer ; the functional layer thickens and then is shed during menstruation in humans . Some other mammals including apes , Old World monkeys , some species of bat , and the elephant shrew menstruate . In most other mammals the endometrium is reabsorbed in the estrous cycle . During pregnancy , the glands and blood vessels in the endometrium further increase in size and number . Vascular spaces fuse and become interconnected , forming the placenta , which supplies oxygen and nutrition to the embryo and fetus . The speculated presence of an endometrial microbiota has been argued against . </P>
when does the uterine lining become more vascular
when does the uterine lining become more vascular
During pregnancy
During pregnancy