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Medicine Notes Gastrointestinal (GI) System Notes

Digestion In The Mouth And Swallowing Notes

Updated Digestion In The Mouth And Swallowing Notes

Gastrointestinal (GI) System Notes

Gastrointestinal (GI) System

Approximately 57 pages

These notes helped me achieve a mark of 73% in my GI exam, which is the equivalent of a 1st. The notes are based on a series of lectures on the subject. They are very clearly laid out and easy to follow. They cut out unnecessary information on the topic, making the notes very concise, and fast to get through. Anyone studying medicine, or any other subject requiring knowledge of the GI tract (e.g. physiology or anatomy), would benefit greatly from these notes. There are lecture in the series on th...

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The following is a more accessible plain text extract of the PDF sample above, taken from our Gastrointestinal (GI) System Notes. Due to the challenges of extracting text from PDFs, it will have odd formatting:

Lecture 4

Digestion in the Mouth and Swallowing

  • Salivary secretion and digestion in mouth

    • Digestion in the mouth

      • No digestion of proteins in the mouth

      • Digestion

        • Starch-----Amylase: pH7-----> Oligosaccharides

      • Motility

        • Chewing= Chop food into small pieces, mix with saliva

        • Swallowing= Move food to lower parts of GI tract

    • Glands

      • Parotid gland

        • Serous (i.e. watery) secretion rich in a-amylase

      • Submandibular and sublingual glands

        • Seromucous secretion

      • Minor salivary glands

        • Scattered throughout oral cavity

        • Mucous secretion rich in mucin glycoproteins

    • Salivary secretion

      • 1.5 litres per day; Hyperosmotic (osmolarity less than that of blood); pH ~7

      • Composition includes

        • Mucin glycoproteins

        • Lysozyme (anti-microbial, protecting from infection)

        • a-amylase

        • Proline-rich proteins (protect enamel/epithelial cells by neutralising tannings, lubrication)

      • Functions

        • Lubricate food, make swallowing easier (mucin glycoproteins, H2O)

        • Clean & protect cavity of mouth (lysozyme, proline-rich proteins)

        • Reduce starch to oligosaccharide molecules (a-amylase)

    • General structure of salivary glands

      • Main collecting duct

      • Interlobular duct (lobule= secretory unit)

      • Intercalated ducts

      • Acinar cell (zymogen granules)

      • Duct epithelial cells

  • Saliva

    • Composition determined by both Acinar and Duct-lining Epithelial cells

      • Acinar cells

        • Generate primary secretion

        • Needed to wash out secretions into mouth (NaCl & H2O)

        • Cl- & a-amylase moves through cells, Na & H20 moves between cells

        • Leaky epithelia

      • Duct-lining epithelial cells

        • Tight epithelium means no movement between Paracellular pathway, unlike in Acinar cells

        • Na+ and Cl- absorbed, HCO3- and K+ secreted

    • Movement of newly synthesized protein through secretory pathway

      • Rough ER (protein production)

      • Golgi (protein modification)

      • Condensing vacuoles (protein packaging)

      • Zymogen granules (final packaging- cells stimulated & material released)

    • Isotonic NaCl secretion by salivary Acinar cells

      1. Na-K pump creates inwardly directly Na+ gradient across basolateral membrane

      2. Na+, K+, 2Cl-: co-transporter (NKCC1) accumulates Cl- ions intracellularly driven by Na+ gradient

      3. Ca2+ activated K+ channels

        • Recycle K+ ions across basolateral membrane

        • Maintain driving force for Cl- exit across apical membrane

      4. Ca2+ activated Cl- channels in apical membrane provide pathway for Cl- to exit cell into duct

      5. Movement of Cl- ions into duct lumen draws Na+ ions & water through Paracellular pathway to complete process of isotonic NaCl secretion

      6. Cholinergic neurotransmitter acetylcholine potently stimulates NaCl secretion by Acinar cells

    • Average composition of parotid saliva as function of flow rate

      • At low flow rate, epithelial cells lining ducts can modify primary secretions

      • Largest increase of Na+ as flow increases, HCO3- is slightly less

      • Cl- steadily rises meaning duct lining epithelial cells have not managed to absorb Cl- (to below level of HCO3- and Na+)

      • Cl- is plateaus at low level

    • Ion channels and transports of salivary duct cells

      1. Na-K pump creates inwardly directed Na+ gradient across BL membrane

      2. Ca2+ activated K+ channels (i) recycle K+ ions across BL membrane

      3. Epithelial Na+ channel (ENaC) mediates absorption of Na+ ions across apical membrane, which are then extruded across BL membrane by Na-K pump

      4. CFTR & anion (Cl-/HCO3-) exchangers mediate apical HCO3- secretion with CFTR recycling Cl- ions, drive HCO3- export from cells

      5. Could be K+/H+ exchanger, but also evidence to suggest it is Ca2+ activated K+ channel

      6. Tight junctions have limited water permeability contributing to hypotonic nature of saliva

      7. Cholinergic neurotransmitter ACh modulates Ca2+ activated K+ channels, CFTR regulated by...

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