The small intestine and disorders

What is the function of the small intestine?

Fluid absorptionPeristalsis (motility)

What is peristalsis?

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.

Name 2 disorders of peristalsis

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

Name the 4 agents that increase motility

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

Name 3 agents that decrease motility

Muscarinic receptor antagonistsOpiates (loperamide)Adsorbents (charcoal)

What is secretory diarrhoea?

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.

Outline the normal control of fluid absorption in the gut.

Na+ is absorbed into the bloodCl- is pulled across into the bloodNaCl is formedWater moves across into the blood to maintain osmosis

During secretory diarrhoea, what happens?

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

How does cholera cause secretory diarrhoea?

Cholera enters the epithelial cellIt causes an increase in cAMPThis activates protein kinases which phosphorylate the Cystic Fibrosis Transmembrane ReceptorThe receptor opensCl- floods into the lumen.

How does E. coli cause secretory diarrhoea?

E. coli enters the epithelial cell.It causes an increase in cGMPThis activates protein kinases which phosphorylate the Cystic Fibrosis Transmembrane ReceptorThe receptor opensCl- floods into the lumen.

Name 4 therapies for secretory diarrhoea.

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)