immune functions nonspecific specific activation of 'humoral' immunity specialised immunoglobulin 'oral tolerance' study mechanism

Activation of immune response

motility origin in gut wall muscularis mucosae muscularis externa smooth muscle coordination 'gap' junctions interstitial cells rhythmogenesis pacemaker potentials need for enteric nervous system example of deficit motility patterns peristalsis - the 'enteric reflex' segmentation the 'migrating motor complex' colonic mass movements defecation disturbed motility pattern (example)

Smooth Muscle Cells, relaxed and contracted Interstitial Cells of Cajal

break

secretion



many digestive secretions, mainly catabolic enzymes

do not confuse

'endocrine' hormone secretion with 'exocrine' digestive enzyme secretion

matching to food types

deficiency uncommonly symptomatic

malabsorption

e.g. cystic fibrosis




few main sites of secretion

pancreatic

hepatic

biliary system and problems

gastric, duodenal, salivary




control of secretion

energy cost to body economy

acid, alkali secretion

enzyme synthesis

inactive precursors

hormonal

enteric reflexes

extrinsic nervous input

References and Advanced Reading. For an overview of motility this is recommended-but only if you have a weekend-a long weekend-without anything else pressing to do: The Motility of the Gastrointestinal Tract. Its beautifully written though-by James Christensen-and covers most of what you might ever want to know about gut motility. Starts off with "Life originated in the watery medium of the primordial seas..." [link valid April '05]. There is a lack of gastrointestinal immunology in Berne & Levy (in fact, no immune system physiology at all!). This link was down when last checked on 6th April 2005; http://www.uicomp.uic.edu/Pathology/infec11.htm but had an interesting description of lymph follicles, which form 'Peyer's patches' in the gut wall (and lymph nodes elsewhere). Suggestions for a replacement link would be appreciated. Material on GI immunity and (many other gut topics) is available at http://www.GastroAtlas.com (need to login first-this is free) but its detailed-may be more useful for looking up particular points [link valid April '05]. Slide credit; AstraZeneca for GastroAtlas "the online version of Mark Feldman's Atlas of Gastroenterology and Hepatology".

Sample multiple-choice question for discussion. Peristalsis (choose the best answer)... a) is symmetrical in direction b) has a basal electrical rate of about 4 cycles per second c) is involuntary (proceeds without forebrain input) d) only occurs when a food bolus stretches the gut wall e) none of the above

The Big Picture: function of the gastrointestinal tract Intestinal Function 2. Crossing the Border: fluid and nutrients at the epithelium Intestinal Function 3. When things don't work out right: pathophysiology of diarrhea