BIOM1060 Lecture Notes - Fall 2018 Lecture 4 - Diuretic, Kidney failure, Lithotripsy
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BIOM1061 Lecture 4
RENAL ANATOMY AND PHYSIOLOGY
ABSORPTION
Reabsorption of sodium
- Majority occurs in proximal tubule (64%)
- In collecting duct: reabsorption regulated by hormone aldosterone
- Transcellular route: across apical membrane (1), diffused through cytosol (2), across
basolateral membrane (3), through interstitial fluid and into capillary
- Paracellular route: through leaky tight functions then interstitial fluid and into capillary
Sodium transport across basolateral membrane
- Na+ most abundant cation in filtrate
- Transport across basolateral membrane = primary active transport
- Active transport: Na+-K+ ATPase pumps Na+ into interstitial space
- Na+ swept by bulk flow into peritubular capillaries (moves down pressure gradient)
Tubular reabsorption of solutes in proximal tubule
- H+ moves out of cell to tubular lumen as Na+ moves into the cell
- In proximal tubule: Na+ reabsorption drives reabsorption of the co-transported
substances and secretion of H+
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BIOM1061 Lecture 4
Reabsorption by PCT cells
1. Na+ pumped into interstitial space by Na+-K+ ATPase (active transport) - creates
concentration gradients that drive:
2. ‘Downhill’ Na+ entry at apical membrane
3. Reabsorption of organic nutrients and ions by cotransport at apical membrane
4. Reabsorption of water by osmosis through aquaporins (increases
concentration of solutes left behind)
5. Lipid-soluble substances diffuse by transcellular route down conc. gradient
6. Ions and urea diffuse by paracellular route down concentration gradient
Transcellular transport system
- Transport maximum exists for almost every reabsorbed substance (reflects number of
carriers in renal tubules available)
- When carriers for solute saturated: excess excreted in urine
Document Summary
Transcellular route: across apical membrane (1), diffused through cytosol (2), across. In collecting duct: reabsorption regulated by hormone aldosterone basolateral membrane (3), through interstitial fluid and into capillary. Paracellular route: through leaky tight functions then interstitial fluid and into capillary. Transport across basolateral membrane = primary active transport. Active transport: na+-k+ atpase pumps na+ into interstitial space. Na+ swept by bulk flow into peritubular capillaries (moves down pressure gradient) H+ moves out of cell to tubular lumen as na+ moves into the cell. In proximal tubule: na+ reabsorption drives reabsorption of the co-transported substances and secretion of h+ Transport maximum exists for almost every reabsorbed substance (reflects number of carriers in renal tubules available) When carriers for solute saturated: excess excreted in urine. Reabsorptive capabilities of renal tubules and collecting ducts. Proximal convoluted tubule: site of most reabsorption (64%) Bulk flow: movement of fluids down pressure or gradient. Makes interstitial fluid hyperosmotic (allows water diffusion from tubule to interstitial fluid)