<Tr> <Th> FMA </Th> <Td> 17742 </Td> </Tr> <Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <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 consists of a single layer of columnar epithelium plus the stroma on which it rests . The stroma is a layer of connective tissue that varies in thickness according to hormonal influences . In the uterus simple tubular glands reach from the endometrial surface through to the base of the stroma, which also carries a rich blood supply provided by the spiral arteries . In a woman of reproductive age, two layers of endometrium can be distinguished . These two layers occur only in the endometrium lining the cavity of the uterus, and not in the lining of the Fallopian tubes . </P>

When does the uterine lining become more vascular