Selective reabsorption

Adaptations of the proximal convoluted tubule

  • microvilli

    • Small, finger-like projections that greatly increase the surface area for reabsorbtion

  • Basal infoldings

    • These structures further increase the surface area for moving substances into surrounding blood capillaries

  • Numerous mitochondria

    • These organelles provide ATP for the active transport processes involved in reabsorption

  • Co transporter proteins in plasma membrane

    • Allow co transport of substances from filtrate into epithelial cells

Reabsorption in the proximal convoluted tubule

  1. Na+ actively transported into blood capillaries

    • Reduces the Na+ concentration in the epithelial cells lining the PCT

  2. Na+ moves from the PCT lumen into the epithelial cells, down its concentration gradient

  3. Na+ is co transported with substances like glucose and amino acids into the epithelial cells

  4. These reabsorbed molecules can then diffuse into blood capillaries

  5. As water potential is increased in the cell water can move through into the blood via osmosis

Distal convoluted tubule function

  • reabsorption of any remaining useful substances

    • Primarily through active transport

  • The alteration of DCT membrane permeability to regulate further reabsorption of water and solutes

  • The regulation of blood pH by selectively reabsorbing certain ions