Proximal Convoluted Tubule

• Some water and all the glucose are selectively reabsorbed back into blood.

  The cells in the PCT have microvilli to increase surface area and many mitochondria to provide ATP for active transport.
• Selective Reabsorption of Glucose:

  1. Sodium ions are actively transported from epithelial cells through a carrier protein into the blood capillaries (creating a diffusion concentration gradient).
  2. Sodium ions diffuse from the PCT lumen into the PCT epithelial cell along with glucose through a co-transport protein.
  3. Glucose enters blood capillary down a concentration gradient by facilitated diffusion through a protein channel.
• The movement of substances into the epithelial cell reduces the cell water potential so water enters cells, then into the capillary, by osmosis down a water potential gradient.
• Other molecules move through different channels.

  There is no channel for urea.
• Describe and explain how these cells are adapted for absorption?

  • Microvilli give large surface area.
  • Many carrier proteins for active transport.
  • Many ribosomes to produce carrier/ channel proteins.
  • Many channel/ carrier proteins for co-transport and facilitated diffusion.
  • Many mitochondria to produce ATP.