Gut Secretion And Absorption

4.10.05

Fluid and electrolyte transport are important functions of the gastrointestinal tract (even in the absorption of food).

Epithelial cells may
• secrete water and electrolytes ie. transport from blood to gut lumen
• absorb water and electrolytes.

Diarrhoea = malabsorption of water.

Movement of water and solutes
• Water moves down osmotic gradients.
• Electrolytes move down electrochemical gradients.
• To move solutes against their concentration gradients, energy is required.
• Energy is supplied by Na+ gradients (generated by Na+ pump) and by H+ gradients.

Water molecules: Paracellular route = between cells.
Ions: Transcellular route = through cells (active or passive transport)

Diarrhoea
• Hypermotility - transport too fast for absorption.
• Osmotic - non-solute absorption.
• Defective transport - Na+ or Cl- transporters absent.
• Secretory
-inflammatory, blood hormones, tumours.
-enterotoxins, viruses/parasites.

Oral rehydration therapy: water, electrolytes, glucose.