Basic mechanisms of placental transfer.
Placental transfer is a complicated form of transmembrane transport. Simple membrane transport is discussed first. The influence of the membrane structure on transport parameters is treated and the effect of a concentration difference on both sides of the membrane is expressed in a simple clearance equation. It is then taken into account that a placental circulation is present and the model is adjusted to a heat exchange analogy. The effect of charge on the solutes to be transported is also considered. When metabolism takes place during transport, the heat exchange model is no longer applicable. A new model is developed to quantitate this kind of transport and is also applied to calculate the synthesis in the placenta. Precursors enter from the fetal and/or maternal circulation and are metabolized in the placental tissues; they then return to both circulations. It is shown that even a simple model such as this is described by rather complex equations and shows a considerable error magnification. This will limit its use to those cases in which the input data itself shows little variation.
D001692:Biological Transport; D004058:Diffusion; D005260:Female; D006358:Hot Temperature; D006801:Humans; D008431:Maternal-Fetal Exchange; D008954:Models, Biological; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy