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Solute Reabsorption - Coggle Diagram

- - - - increases Na transport upon activation
  - - - enhance salt reabsorption from both TAL and CD via increased NKCC2 (Na-K-Cl cotransporter)
      - increased activity of ENaC in CD
  - - - inhibits Na-K pump amongst other Na channels
- - - - Transcellular pathway
        
        lumen to cell to interstial fluid
        
        passing cell from apical plasma membrane to cytoplasm to basolateral plasma membrane
      - Paracellular pathway
        
        lumen to intercellular space via tight junction to interstitium
        
        either via passive diffusion or solvent drag
    - - using starling law (net movement created from opposing hydrostatic prssure and oncotic pressure) where peritubular capillaries that originate from efferent arteriole has low hydrostatic pressure and high oncotic pressure
        
        favours fluid and solute uptake from interstitium into blood stream
    - - Na
        
        Intracellularly
        
        Down gradient, Na moves through apical p.m. via cotransporter
        
        chemical gradient created by Na-K-ATPase (or Na-K pump) on basolateral membrane
        
        Paracellularly
        
        follows Cl that moves paracellularly due to electrostatic attraction
      - Cl
        
        Intracellularly
        
        electrical gradient created from Na-K pump favours Cl movement into cell via cotransporter
        
        absorption of other solutes left Cl in the tubule lumen and creates gradient for Cl to enter cells
        
        Paracellularly
        
        via passive diffusion as tight junction is highly permeable to Cl
      - HCO3-
        
        enters as H20 and CO2 via apical carbonic anhydrase
        
        H provided by Na-H antiporter where Na enters cells, H exits
        
        cytoplasmic carbonic anhydrase hydrolyzes the components back to HCO3-
        
        HCO3 exits basolateral p.m via
        
        Na-HCO3 cotransporter
        
        Na-dependent HCO3-/Cl antiporter
      - Ca
        
        via solvent drag through paracellular pathway
        
        65% are reabsorbed here
      - K
        
        passive diffusion via paracellular pathway
      - Low molecular weight proteins such as insulin, glucagon, PTH
        
        via endocytosis
      - other solutes such as glucose, phosphate, sulfate, citrate and amino acids
        
        move via secondary active transport
      - Peptides
        
        broken down by peptidase on apical p.m.
        
        reabsorbed via Na cotransporter
        
        short chain peptides via H cotransporter
  - - - Endogenous organic ions or exogenous drugs or toxins
        
        poorly filtered by glomerular filtration due to being protein bound, must be secreted for elimination
        
        provides basis for urine testing
        
        p-aminohippurate is used to estimate renal plasma flow
        
        tubular antiobiotics secretion to determine effective antibiotics to treat UTI
- - - - Solutes
        
        Na
        
        Basolateral Na-K pump creates electrochemical gradient
        
        Na enters apical via NA-K-Cl co transporter in TAL
        
        inhibited by loop diuretics such furosemide and bemetanide
        
        Na exits basolateral to interstitial fluid via this pump
        
        moves down chemical gradient via apical NaCl cotransporter in DCT
        
        Cl
        
        exits via ClC-K channel aka barttin Cl channel driven by electrical gradient in DCT
        
        Barttin is inhibited by thiazide diuretics
        
        exits basolateral p.m. via Cl channels in TAL
      - both have tall epithelium, and abundance mitochondria to support active transport
  - - - secreted into lumen via apical K channel
- - - - thin ascending for Na reabsorption
      - thin descending for water reabsorption
- - - - Collecting Duct is composed of two main types of cells
        
        Intercalated cells
        
        Have apical ENaC or epithelial Na Channel
        
        thus primarily for NaCl reabsorption driven by gradient created by Na-K pump
        
        account for 2/3 of the cells in superficial part of duct (initial CD, cortical CD, outer medullary CD)
        
        Principal cells
        
        have Cl/HCO3- exchanger aka pendrin
        
        mediates luminal Cl uptakes
        
        also enhances ENaC activity of intercalated cells, thus NaCl reabsorption
    - - K has high intracellular concentration thanks to Na-K pump
      - K is secreted via apical ROMK and BK
      - occurs due to 2 reasons
        
        apical ROMK more permeable than basolateral ROMK
        
        negatively charge lumen electrical potential that favors K secretion
    - - reabsorbed via active transport of H-K pump found abundant in intercalated cells
      - when body needs K
        
        Increased activity of H-K pump
        
        Increased expression of H-K pump in the collecting duct
        
        ROMK and BK activity is inhibited