15.6 selective reabsorption

adaptations of proximal convoluted tubule (PCT):

PCT lined w specialised epithelial cells (adapted to help reabsorb various substances ex. glucose, amino acids, chloride + sodium ions, water from filtrate back → bloodstream)

Key adaptations of epithelial cells in proximal convoluted tubule:

• Microvilli: increase SA for reabsorption.

• Basal infoldings: further increase SA for substance movement into surrounding capillaries.

• Numerous mitochondria: provide ATP for active transport during reabsorption.

• Co-transporter proteins in plasma membrane: enable co-transport of substances from filtrate into epithelial cells.

reabsorption in PCT:

• Reabsorbs most glucose, amino acids, ions, and 85% of water.

• reabsorption process:

  1. sodium ions (Na⁺) actively transported → blood capillaries, reduces Na⁺ conc in epithelial cells lining PCT

  2. Na⁺ moves from PCT lumen → epithelial cells, down conc gradient

  3. Na⁺ co-transported w substances ex. glucose, amino acids → epithelial cells

  4. reabsorbed molecules can then diffuse → blood capillaries

role of distal convoluted tubule (DCT):

reabsorption process:

• makes final adjustments to filtrate’s content: reabsorbs water + salts via active transport

• adjusts membrane permeability for further reabsorption

• regulates blood pH by reabsorbing specific ions

• microvilli + mitochondria assist in reabsorption

• hormones influence adjustments, fine-tuning urine composition