The effects of smoking on placental membranes

Ingested tobacco smoke contains many toxic components that may harm the membrane compartments of the human placenta. The effects of maternal smoking on placental membrane structure are examined by stereological methods and related to smoking habit. A significant decrease in fetal capillary volume and increase in the diffusion distance across the trophoblastic epithelium is observed. The stereologically-determined structural variables are used to estimate both total and partial oxygen diffusive conductances. The total diffusive conductance is found not to alter with smoking; however, changes in partial conductances and the haematocrits of both maternal and fetal blood, indicate hypoxic stress is associated with smoking. However, a component of the placental membranes responsible for the transport of alanine is shown to be altered. An increase in the sodium-dependent transport of alanine across the microvillous border membrane of the placenta is observed in tissues derived from mothers who smoke. This may be an adaptive response to a deficient supply of this amino acid to the placenta.