GI Physiology introduction - GI system

Physiology introduction

4 layers:
 Mucosa
 Submucosa
 Muscularis externa
 Serosa


Circular or spiral folds – first layer of SA amplification

Vectorial transport is only possible because cells are polarised having apical and
basolateral membranes

Paracellular pathway – Passing through the intercellular space between the cells.

Transcellular pathway - substances travel through the cell, passing through both
the apical membrane and basolateral membrane.

Transcellular transport of Cl- drives paracellular movement of water and Na+
ions. Sodium ions move to neutralise charge across the epithelium.




NKCC1 is the main mechanism to bring in Cl- into the cell to drive secretion.

GI tract secretes 8-9 litres per day