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Digestion/Absorption: Fluids & Electrolytes - Basics (general…

- - - - ~48-96 hrs
      - sloughed into lumen
      - dec during starvation & vice versa
  - - - resistance increases away from mouth & down crypt
      - dependent on paracellular resistance (tight jxn permeability)
- - - - (+) secretion
      - agonists
      - categories:
        
        hormones & NTs (VIP, guanylin, Ach, bradykinin, serotonin)
        
        immune regulatory products (histamine, prostaglandins)
        
        laxatives (bile acids, ricinoleic acid)
        
        bacterial enterotoxins (cholera, E.coli, yersinia, C. diff)
      - inc. 2nd messengers (cAMP, cGMP, Ca)
      - cholera
        
        binds apical receptors on crypt cells
        
        inc. cAMP >> Cl secretion by CFTR
        
        Na & H2O follow Cl into lumen
        
        cAMP (-) Na absorption
        
        secretory diarrhea & rice water stool symptom
    - - (+) absorption
      - neural, endocrine & paracrine factors
      - few agonists
      - categories:
        
        somatostatin & NE: (+) electroneural salt abs >> inhibits electrogenic HCO3 secretion
        
        glucocorticoids
        
        mineralocorticoids
    - - dietary component not abs (lactose intolerance)
    - - secretion of F&E from intestine
      - induced by secretagogues (i.e. enterotoxins)
      - no affect on nutrient-coupled Na absorption
      - Oral Rehydration Solution
        
        inc [glucose] &/or [a.a.] in lumen >> inc. Na reuptake
        
        inc. intra[Na] >> Na,K-ATPase
        
        solution w/ varing conc. of glucose, Na, Cl & HCO3
        
        reverses dehydration & metabolic acidosis