Mechanisms by which substances are transferred across the placenta

• Diffusion or the movement of particles (molecules or ions) from a region where they are comparatively concentrated to a region where they are at lower concentration for example oxygen from the mother’s blood to the foetus and carbon dioxide from foetal blood the mother.
• Facilitated diffusion: this is a type of passive transport that allows substances such as glucose to cross membranes to the foetal blood with the assistance of special transport proteins.
• Osmosis: this is the passage of water molecules from a region of their high concentration to a region of their low concentration through a partially permeable membrane/placental membrane.
• Active transport: It energy-consuming transport of molecules or ions across a membrane against a concentration gradient. Substances usually transported across cell membrane by active transport include Na+, K+, ureate ion and amino acids
• Exocytosis: This is the process by which large particle are taken in through the placenta cell. It provided a means by which enzymes, hormones, antibodies and cell wall precursors are released from the cells. Here a vesicle containing the material moves towards the surface of the cell and fuse with the plasma membrane. The vesicle the opens to the exterior and its contents leave the cells
• Endocytosis: This provide a means by which big objects are taken by the cell. First the plasma membrane invaginates to form a flask-shaped depression which envelops the material. The neck of the flask then closes, and the invagination becomes sealed off to form a vesicle which moves into the cell. When a liquid like substance is taken in by the cell the process is referred to as pinocytosis. And solid particles are taken in by phagocytosis.

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Dr. Bbosa Science