Physiology - GI - DIGESTION AND ABSORPTION - BASIC MECHANISMS

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  1. List three anatomical and histological levels at which digestion takes place. Distinguish between mechanical and chemical destruction and give examples of each.
    s
  2. Compare the anatomical, physiological and enzymatic features of the stomach, small intestine and colon that influence their ability to absorb nutrients and water.
    s
  3. Digestion takes place at three levels: __________.
    lumen, mucosa (brush border) and cytosol
  4. Lumenal digestion is both ______.
    mechanical and chemical
  5. Mechanical destruction
    - mouth: _____
    - stomach and intestine: ______
    - reduces foods to _____.
    Chemical destruction
    - primarily involves _____
    - mouth: digestion of _______
    - stomach: _____ digestion of _______.
    - small intestine:
        - most active
        - ______ are essential to digest ______.

    - ________: final degradation of carbohydrates and proteins
    - _______: final lipid digestion
    - _______: digestion of major nutrients completed

    - further digestion by cytosolic enzymes: ________
    • chewing
    • motility
    • smaller units

    • enzymes
    • starch and triglycerides
    • limited / proteins and lipids
    • pancreatic enzymes 
    • starches, proteins, and lipids

    • brush border enzymes
    • bile salts

    terminal ileum

    peptide chains of a few amino acids
  6. Absorption
    • - transport substances
    • - from gut lumen
    • - across mucosal surface or through tight junctions
    • - into blood
  7. primary site of nutrient and water absorption
    small intestine
  8. Factors influence absorption of nutrients
    • - Membrane Permeability
    •     - more permeable to ions and small molecules
    •     - decreased resistance of tight junctions
    •     - 2x larger pore diameters
    •     - decreasing permeability gradient from duodenum to ileum

    • - Enzymes
    •     - small intestine: reduce to simple molecules

    • - Surface Area
    •     - folds, villi, and microvilli
    •     - ~200 square meters surface area

    • - Specialized Transport Systems
    •     - most important to rapid absorption
    •     - transporters: crypt cells -> villus tips -> apoptosis every 4-6 days (rapid renewal)
  9. Balance between absorption by villus tip cells and secretion by crypt cells
    • - Nutrient transport facilitates water absorption
    •     - paracellular: cell junctions
    •     - transcellularly: specialized water channels
    • - major driving force: apical Cl chan,  CFTR
  10. crypt cells: _____
    villus cells: _____
    • secret water and ions
    • absorb water and ions
  11. Some simple substances (glucose) do not require further digestion: _______

    Oligomers (sucrose): digested into monosaccharides (glucose and fructose) by ________ prior to absorption

    Large polymers (proteins): digested into monomers (amino acids) by _______

    Some oligopeptides (small chains of 2-3 amino acid): ________

    Triglycerides: _______
    - absorbed by the intestinal cell as ingested

    - brush border enzymes

    - pancreatic enzymes and then absorbed

    - absorbed directly and further digested to monomers by cytosolic proteases

    - converted to smaller compounds, primarily, glycerol and fatty acids, absorbed and then reassembled inside the cell

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Author:
akhan
ID:
315901
Filename:
Physiology - GI - DIGESTION AND ABSORPTION - BASIC MECHANISMS
Updated:
2016-02-14 16:24:11
Tags:
physiology GI
Folders:
physiology
Description:
Physiology - GI - DIGESTION AND ABSORPTION - BASIC MECHANISMS
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