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List three anatomical and histological levels at which digestion takes place. Distinguish between mechanical and chemical destruction and give examples of each.
Compare the anatomical, physiological and enzymatic features of the stomach, small intestine and colon that influence their ability to absorb nutrients and water.
Digestion takes place at three levels: __________.
lumen, mucosa (brush border) and cytosol
Lumenal digestion is both ______.
mechanical and chemical
- mouth: _____
- stomach and intestine: ______
- reduces foods to _____.
- 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: ________
- smaller units
- starch and triglycerides
- limited / proteins and lipids
- pancreatic enzymes
- starches, proteins, and lipids
- brush border enzymes
- bile salts
peptide chains of a few amino acids
- - transport substances
- - from gut lumen
- - across mucosal surface or through tight junctions
- - into blood
primary site of nutrient and water absorption
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)
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
crypt cells: _____
villus cells: _____
- secret water and ions
- absorb water and ions
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): ________
- 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