<Tr> <Td> Progesterone - dependent carbonic anhydrase </Td> </Tr> <Tr> <Td> Lactoferrin </Td> </Tr> <P> Not only the lining of the uterus transforms, but in addition, the secretion from its epithelial glands changes . This change is induced by increased levels of progesterone from the corpus luteum . The target of the secretions is the embryoblast, and has several functions on it . </P> <P> The embryoblast spends approximately 72 hours in the uterine cavity before implanting . In that time, it cannot receive nourishment directly from the blood of the mother, and must rely on secreted nutrients into the uterine cavity, e.g. iron and fat - soluble vitamins . </P>

Where does implantation and formation of the placenta normally occur