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Small Intestine. Prof. K. Sivapalan. Small Intestinal Motility. Segmental movement [mixing 7/min in ileum] Peristalsis [propagation average 1 cm/min]. Stimulated by stretch of the wall (dietary fibers). Obstruction causes over distention and violent peristalsis which causes colicky pain.

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Small Intestine


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small intestine

Small Intestine

Prof. K. Sivapalan.

small intestinal motility
Small Intestinal Motility
  • Segmental movement [mixing 7/min in ileum]
  • Peristalsis [propagation average 1 cm/min].
  • Stimulated by stretch of the wall (dietary fibers).
    • Obstruction causes over distention and violent peristalsis which causes colicky pain.
  • Facilitated by,
    • Parasympathetic stimuli
    • Gastro-enteric reflex.
  • Inhibited by,
    • Sympathetic stimuli.
  • Irritation to mucosa can cause peristaltic rush and diarrhoea.
  • Injury to peritoneum causes reflex inhibition and paralysis of the intestine- Paralitic ileus.
  • Migrating Motor Complex

Small Intestine

intestinal secretions
Intestinal Secretions
  • Brunner’s glands in duodenum secrets thick mucus in response to acid to protect from acid.
  • Crypts of Liebercühn
    • water and electrolytes similar to ECF, 2000 ml/day [?Much more]
    • Enzyme enterokinase.
    • Cell division and migration to top of villi- life span of the epithelial cell is 5 days
  • Control of crypts of Liebercühn -
    • autonomics- no effect
    • VIP- vasodilatation, may stimulate.

Small Intestine

intestinal villi
Intestinal Villi
  • Surface area:
    • Intestine [cylinder]- 0.33 M2
    • Valvulae c.- 1.00 M2
    • Villi- 10.0 M2
  • Microvilli- 200 M2
  • Surface enzymes:
    • Disaccharidases
    • Peptidases
    • Nucleic acidases
  • Cells at the top face constant aberration and hypoxia

Small Intestine

fat absorption
Fat Absorption
  • Fat is emulsified by bile salts and lipase digests it.
  • Micelles formed in the presence of bile salts.
  • Fatty substences diffuse into the mucosal cell.
  • Chylomicrons formed and released by exocytosis into ECF.
  • Chylomicrons are taken by the lymph vessels.

Small Intestine

absorption of cho and protein
Absorption of CHO and Protein.
  • Na+ pushed into ECF by active transport
  • Na+ enters cell from lumen.
  • The channel is a co-transporter of glucose, maltose and amino acids, peptides.
  • This is secondary active transport - Importance of salt and glucose in re-hydration.
  • Rate of absorption and dietary fibers

Small Intestine

circulation in villus
Circulation in Villus
  • Every villus has a central lacteal which transports chylomicrons.
  • Blood with oxygen goes towards the tip and nutrients away from the tip.
  • Arrangement of vessels sets up counter current flow preventing transport of oxygen to tip and nutrients out.
  • The muscle in the villus contracts from time to time and empties it into the circulation.

Small Intestine

illeo caecal valve
ILLEO-CAECAL Valve

Small Intestine