Term
| Consequence of Na imbalance |
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Definition
Na affects the ECF volume. High sodium results in high ECF volume, leads to high BP, cardiac overload, and CHF.
Low Na leads to hypovolemic shock.
The body tightly regulates Na levels within +/- 10 mEq/d |
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Term
| Fractional reabsorption of Na along nephron |
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Definition
1. Proximal tubule: 67%
2. Loop of Henle: 25%
3. Distal convoluted tubule: 5%
4. Collecting Duct: 3% |
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Term
| Na handling in early proximal tubule |
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Definition
Na goes from lumen to interstitial space
Transcellular transport:
a. Lumen side
Has many cotransporters (Glucose, Na symporter, Na, H antiporter, etc.)
Some transport is electrically neutral while some is electrogenic, leaves lumen with a slight negative charge compared to the interstitial space.
b. Interstitial side
Na transported out to interstitial space using Na, K ATPase (main) and Na, HCO3- symporter (minor).
Paracellular movement:
1. Slightly negative lumen causes Na to backleak through tight junctions (waste).
2. Water forms a solvation shell around Na and follows osmotic gradient (solvent drag). |
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Term
| Na handling in thick ascending limb |
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Definition
Transcellular transport
a. Lumen side
Na is reabsorbed through the Na, K, Cl symporter and the Na, H antiporter.
b. Interstitial side
Na goes through Na, K ATPase to reach the interstitial fluid.
b. Paracellular
K channels let K leak back into lumen. Buildup of positive charge is driving force for Na to diffuse into the interstitial fluid. |
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Term
| Na handling in the distal convoluted tubule |
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Definition
Transcellular
a. Lumen side
Na, Cl symporters (target for Thiazide diuretics) reabsorb Na. This creates a negative charge in the lumen.
b. Interstitial side
Na, K ATPase transports Na to interstitial fluid.
Paracellular
No paracellular transport. |
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Term
| Na handling in in cortical collecting tubule |
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Definition
Transcellular
a. Lumen side
Na enters through Na channels, creates negative charged lumen. Creates driving force for K into lumen.
b. Interstitial side
Na, K ATPase
No paracellular transport |
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Term
| Cl handling in proximal convoluted tubule |
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Definition
Negatively charged lumen due to Na, Glucose electrogenic symport.
This provides a driving force for paracellular diffusion of Cl into interstitial fluid.
Solvation drag of Cl is a minor component of paracellular transport.
No transcellular transport. |
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Term
| Cl handling in late proximal straight tubule |
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Definition
Transcellular
a. Lumen side
Cl enters through Cl, base antiporters.
b. Interstitial side
Cl goes to interstitial fluid through Cl channels and Cl, K symporters.
Paracellular
Cl diffuses with Na. |
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Term
| Cl handling in thick ascending limb |
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Definition
Transcellular
a. Lumen side
Cl enters through Na, K, Cl symporter.
b. Interstitial side
Cl channels offset Cl reentry through HCO3-, Cl antiporters. |
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Term
| Cl handling in distal convoluted tubule |
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Definition
Transcellular
a. Lumen side
Na, Cl symporter
b. Interstitial side
Cl channel |
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Term
| Cl handling in the principle cell of cortical collecting tubule |
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Definition
| Lumen voltage of (-20)-(-30)mV drives Cl paracellularly to interstitial fluid. |
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Term
| Cl handling in beta cell of the cortical collecting tubule |
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Definition
Transcellular
a. Lumen side
Cl, HCO3- antiporter (mostly found in herbivores)
b. Interstitial side
Cl channel |
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Term
| Water transport in nephron |
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Definition
Always passive transport, driven by osmotic pressure.
Proximal tubule=high permeability with leaky tight junctions. However, transcellular transport is greater than paracellular due to aquaporin channels.
Thin descending limb=moderate permeability.
Ascending limb and beyond=impermeable
Arginine vasopressin increases water permeability in later portions of nephron. |
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Term
| Regulators of Na transport |
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Definition
1. Glomerulotubular balance
2. Antinatriuretic neurohormonal factors (predispose reabsorption of Na)
3. Natriuretic neurohormonal factors (predispose excretion of Na) |
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Term
| Glomerulotublar balance and Na regulation |
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Definition
Maintains the same fraction of Na secretion and reabsorption over a wide range of GFRs.
Depends on solute balance, solute delivery, and Ang II (questionable). |
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Term
| Antinatriuretic neurohormonal factors |
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Definition
1. Aldosterone: increases NaCl reabsorption in the cortical collecting tubule principle cells.
2. Sympathetics: Increases vascular resistance which decreases flow, increases reabsorption. Also directly stimulates Na reabsorption.
3. Arginine Vasopressin: stimulates Na reabsorption in thick limb and cortical collecting tubule principle cells. |
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Term
| Natriuretic neurohormonal factors |
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Definition
1. ANP: increases Na excretion by increasing GFR.
2. ATPase inhibitors inhibit Na, K ATPase
3. Dopamine: Increases RPF and GFR, inhibit Na, H antiporter and Na, K ATPase.
4. Bradykinin/Prostaglandins: Reduces Na reabsorption. |
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