1. Gastro-intestinal tract
Sophie Young
27th June 2007

2. Objectives Anatomy Physiology Physiology of vomiting Motility
Secretory
Digestion
Absorption
Physiology of vomiting

3. Anatomy Taken from http://human. freescience
Anatomy Taken from htmx/parts/organ_systems/gastrointestinal_tract.php

4. GI Motility Basic contractile unit
Na/K/ATPase pump – transmembrane potential
Basic electrical rhythm – slow wave activity
Rhythmical depolarisation + repolarisation
Gap junctions (stomach vs colon)
Frequency + amplitude of slow wave activity affected by:
Autonomic nervous system
Hormones
Drugs

5. Control of GI Motility Intrinsic neuronal control
Myenteric plexus (Auerbach’s)
Cholinergic (+ve), adrenergic (+ve), NANC neurones (-ve)
Integrates all information
Extrinsic neuronal control
Somatic and autonomic control
Chemical control
Neurocrine, paracrine and endocrine

6. Localised GI Motility Swallowing
Motor reflex- voluntary, pharyngeal + oesophageal stages
Gastric motility
Fundus – prolonged tonic contractions
Antrum – slow wave activity, pylorus affected by fasted and fed states (?hormonal + neuronal control), composition of chyme in duodenum
Bowel
Small – slow wave activity, various types of activity
Large – slow propulsion + mass movements

7. Secretory function of GI tract
Salivary glands – under Autonomic control
Lubrication  Buffer
Digest starch (amylase pH dep)  Antibacterial/viral
Digest fat (lipase, pH indep)
Gastric
Oxyntic glands – chief cells (pepsinogen)
(all gastric mucosa – mucus cells
except lesser curve) – parietal cells (HCl + intrinsic factor)
Pyloric glands – G cells (gastrin)
(pylorus) – mucus cells

8. Control of gastric secretions
Cephalic stage - gastrin
Gastric stage - gastrin
Intestinal stage - gastrin

9. Secretory function of GI tract
Pancreatic
Stored as proenzymes
Fat/protein – stimulus for release
Secretin, cholecystokinin and vagus mediated
Biliary
Emulsification of fat globules in SB
Enterohepatic circulation of 94% bile salts

10. Digestion Carbohydrates Cellulose -  glucose linkage, indigestible
Salivary and Pancreatic Amylases
Oligo-/Disaccharides
Brush border enzymes eg lactase/sucrase
Monosaccharides
Glucose Fructose Galactose
Cellulose -  glucose linkage, indigestible

11. Digestion Protein Pepsin (stomach) Trypsin/chymotrypsin (SB)
Polypeptides
Carboxypeptidase (pancreas)
Aminopeptidase (brush border)
Amino acids Monopeptides Dipeptides
Hydrolysis in epithelial
cell after absorption
Amino acids

12. Digestion Fat Triglycerides (90% dietary fat)
Lingual + pancreatic lipases
Free fatty acid Monoglycerides
Combine with bile salts + cholesterol
Micelles

13. Absorption Carbohydrates
Taken from

14. Absorption Protein Secondary active transport across apical membrane
Di/tripeptides hydrolysed to
amino acids
Facilitated diffusion into
blood
Taken from

15. Absorption
Fat
Taken from

16. Absorption Vitamins Fat Soluble – micelles
Water Soluble: B1- active in jejunum, C - active + passive in SB, Folic acid – active in SB, B12 – combines with IF ?pinocytosis in terminal ileum
Sodium and Chloride
Na – cotransporter mechanism, Cl – colonic uptake
Water
SB + colon – ANS and hormone control
Iron and Calcium

18. Physiology of Vomiting Protective physiological function against ingested toxins

19. 3 distinct phases
Nausea: unpleasant sensation that immediately proceeds vomiting. 
Retching: follows nausea and comprises laboured spasmodic respiratory movements against a closed glottis with contractions of abdominal muscles, chest wall and diaphragm without any expulsion of gastric contents.
Vomiting: as for retching but with the opening of gastric cardia, resulting in rapid + forceful evacuation of stomach contents up to and out of the mouth

20. Vomiting
Reflex mechanism – sensory afferents, central integrative centre, motor efferents
Sensory afferents
GI – vagally mediated mechanoreceptors and chemoreceptors
CTZ – area postrema 4th ventricle, outside blood-brain barrier, many receptors present:
Muscarinic Serotonergic (5HT3) Opioid ()
Histamine (H1) Dopaminergic (D2) Adrenergic (1 + 2)
Vestibular system – labyrinthine stimulation
Cortex

21. Taken from www.frca.co.uk

22. Vomiting ‘Vomiting Centre’
Oversimplication, probable multiple discrete interconnecting areas within medulla
Motor efferents
Pre-ejection: nausea, sympathetic activity, vagal mediation proximal stomach relaxation + retrograde SB contraction
Ejection: retching – perioesophageal diaphragm contracted, vomiting – perioesophageal diaphragm relaxes to expel contents with halting of respiration

23. Taken from http://www. nauseaandvomiting. co

25. References Pinnock et al (2003) Fundamentals of Anaesthesia
Vander et al (1998) Human Physiology
Anaesthesia UK