anatomy of the umbilical cord. cross-sectional diagram of human umbilical cord. fetal circulation. biology of the human

placenta maternal surface fetal biology human maternity reproductive anatomical system fetus illustration structure umbilical pregnancy pregnant womb uterus medical newborn medicine reproduction growth artery vein embryo anatomy woman prenatal diagram vector childbirth child blood cord cross sectional circulation section cell arteries perivascular intervascular subamniotic wharton allantois duct jelly amnion