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Introduction To The Gi Tract Notes

Medicine Notes > Gastrointestinal (GI) System Notes

This is an extract of our Introduction To The Gi Tract document, which we sell as part of our Gastrointestinal (GI) System Notes collection written by the top tier of Bristol University students.

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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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