The small intestine and disorders

• Fluid absorption
• Peristalsis (motility)

Peristalsis is the co-ordinated contraction of the gut, allowing nutrients and fluid to be absorbed. It is caused by the action of the mesenteric plexus on the circular and longitudinal muscle which are perpendicular to each other. The mesenteric plexus is activated by Acetylcholine.

• Hypomotility (excessive fluid absorption)
• Hypermotility (insufficient fluid absorption)

• Bulk and osmotic laxatives (retain water)
• Faecal softeners (detergent-like)
• Stimulant purgatives (increase secretion-increase motility)
• Cholinergic agonists (cisapride)

• Muscarinic receptor antagonists
• Opiates (loperamide)
• Adsorbents (charcoal)

• Worldwide principal cause of early death.
• Associated with stress, drugs and infection eg cholera.
• Increased motility and increased fluid secretion into the lumen.
• Body is releasing water into the bowel when it shouldn't be.

• Na+ is absorbed into the blood
• Cl- is pulled across into the blood
• NaCl is formed
• Water moves across into the blood to maintain osmosis

• A stimulus triggers the movement of Na+ into the lumen.
• Cl- follows the Na+ into the lumen
• Water enters the lumen to try and maintain osmosis

• Cholera enters the epithelial cell
• It causes an increase in cAMP
• This activates protein kinases which phosphorylate the Cystic Fibrosis Transmembrane Receptor
• The receptor opens
• Cl- floods into the lumen.

• E. coli enters the epithelial cell.
• It causes an increase in cGMP
• This activates protein kinases which phosphorylate the Cystic Fibrosis Transmembrane Receptor
• The receptor opens
• Cl- floods into the lumen.

• Fluid and salt/glucose (fluid for rehydration, glucose facilitates the uptake of sodium in the gut)
• Anti-secretory drugs eg Loperamide (more severe cases)
• Antibiotics (immunocompromised patients)
• Vaccines (eg for S. Typhi)