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Introduction To The Gi Tract Notes

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Lecture 2 Introduction to the GI tract

Functions of GI system o Ingestion (taking in food) o Digestion
 Food & large molecules chemically degraded to produce smaller molecules o Absorption
 Nutrient molecules absorbed by cells that line GI tract & enter blood o Egestion (removal of waste) Structure of GI tract o See lecture notes Epithelia of the gastrointestinal tract o Turnover of cell layer in a couple of days o Types of cell
 Absorptive cells
 Goblet cell (mucous cell)
 Microvacuolated columnar cell (will absorb salt and water)
 Stem/progenitor cell
 Enteric endocrine cell (secrete paracrine/hormonal factors to help digestion) o Absorptive cell (small intestine)
 Paracellular pathway (H2O)
 Transcellular pathway (Na+/glucose transporter; Na+/K+ ATPase)
 Absorption across basolateral membrane o Secretory cell (stomach)
 Lots of Golgi apparatus and mitochondria
 Secretion across apical membrane into lumen of intestine Movement of salt and water across intestinal epithelium

1. Sodium-potassium NKCC1 pump sets up gradient to allow Cl- pump to work

2. Cl- passively moves from high to low concentration passively

3. Na+/K+ ATPase 2

4. K+ channel to remove K+ to allow NKCC1 function

5. H2O and Na+ move into lumen paracellularly Gastrointestinal secretions o Five major secretory tissues
 Salivary glands; Gastric glands; Exocrine pancreas; Liver-biliary system; Intestine o Total secretion= 8-9 litres/day o Containing: enzymes, ions, water, mucus etc. o Function: Breakdown large compounds, regulate pH, dilute, protect etc. Blood circulation of GI tract o Exuberant blood supply in villi & GI o Central Lacteal where fats are absorbed and taken into blood stream o Splanchnic circulation
 Organised so important things absorbed are taken to liver first instance
 After meal, 8 fold increase in splanchnic circulation
 Most blood delivered where needed in tract

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