FUNCTION OF PLACENTA
Picture: Diagrammatic section of a portion of the placenta.
The villi are looked like tree with branches, the intervillous space are filled with mother's blood, red and blue in color.
Placental production of hormones necessary for the continuation of pregnancy.
Human chorionic gonadotropin [HCG] is produced from the first week after implantation, and is secreted into the mother circulation [but not the fetal circulation].The HCG aids in the maintenance of the corpus luteum of pregnancy and is the basis for the Aschheim-Zondek and Friedman pregnancy tests.
Estrogens are bound to serum albumin in the maternal circulation and there for metabolized slowly.
Progesteron on the other hand, is unbound and is metabolized rapidly.
Corticoids are held in relatively inactive form by a plasma protein.Thus, although the titer of hydroxyl-corticosteroids is high during pregnancy.
Placental transfer across the placental barrier by different processes:
Diffusion: Substances required for the growth of fetal life and the elimination of its waste products are handled largely by diffusion across the placental barrier. Included in these group are oxygen, water, electrolytes, water soluble vitamin [B-Complex and C] traverse the plasma easily, Vitamin A, D, E and K also pass the placenta, CO2 [carbon dioxyde] and urea. Substances of low molecular weight [less than 1000]diffuse across the placenta with ease. Large molecules [with molecular weight more than 1000] such as blood proteins will not pass the placental by diffusion.
Selective transfer: Enzymatic processes, often involving slight energy exchange, supply many fetal nutritional needs. Glucose, amino acids, calcium, phosphorus, iron cross the placenta by this means. Essential amino acids are transferred more rapidly than polypeptides.
Pinocytosis: The particles are carried across the cell virtually intact to be released on the other side, whereupon they promptly gain access to the fetal circulation. Complex proteins, small amounts of fat, and perhaps immune bodies may traverse the placenta in this way.
Leakage through defects: Trophoblastic endothelial junctions may “leak” small amounts of plasma and blood cells. Maternal and fetal blood may mix as a result of the defects.
FETAL NUTRITION [next topic]