Term
| Effects of loss of K in cells |
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Definition
| Cell shrinks and acidosis occurs. Loss of enzymes and slower/halted protein synthesis and stunted growth may also occur. |
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Term
| Effects of gain of K in cells |
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Definition
| Cells swell and alkalosis occurs. |
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Term
| Difference in renal handling of Na and K |
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Definition
| Na is only filtered and reabsorbed while can also be secreted. |
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Term
| Promoters of cell uptake of K |
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Definition
1. Insulin
2. Aldosterone
3. Beta adrenergic agonists
4. Alkalosis |
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Term
| Promoters of cell release of K |
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Definition
1. Acidosis
2. Hyperosmolarity
3. Alpha adrenergic agonists
4. Cell lysis |
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Term
| Effect of acidosis on intracellular K content |
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Definition
Reduces levels of intracellular K through
1. Inhibiting Na, K ATPase
2. Inhibiting Na, K Cl Exchanger
3. Protons are bound to proteins that originally bound K. K then exits cell through K channels. |
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Term
| How body handles excess K |
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Definition
Large amounts of extracellular K is fatal.
K is first stored intracellular (sequestered), before excretion 12-24 hours later. |
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Term
| Overview of K handling in the nephron |
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Definition
1. 80% reabsorbed in proximal tubule
2. 10% reabsorbed in the loop of Henle
3. Distal nephron balances K levels in cell, can either reabsorb up to 8% in times of low K or secrete as much as 150% with high K levels. |
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Term
| K handling in the proximal tubule |
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Definition
Paracellular
In early part of proximal tubule, there is a negative charge in lumen because of net loss of Na. Solvent drag plays a role in paracellular transport in early part of proximal tubule.
In late stage of the proximal tubule, the lumen is positive, which provides driving force for K movement into interstitial fluid. |
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Term
| K Handling in the thick ascending limb |
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Definition
Transcellular
a. Lumen
Na, K, Cl Exchanger
b. Interstitial
K channel
Paracellular
Positive charged lumen creates driving force for K. |
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Term
| Purpose of medullary K reabsorption |
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Definition
| K reabsorption in the medulla is used to fuel the Na, K ATPase for optimal sodium reabsorption. |
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Term
| Purpose of apical K channels |
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Definition
| Replenishes tubular supply of K so that Na loop reabsorption is not impaired (Na, K, Cl exchanger) |
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Term
| K handling in alpha intercalated cell of cortical collecting tubule |
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Definition
Lumen:
K, H antiporter
Interstitial
K channel |
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Term
| K handling of principle cell of cortical collecting tubule |
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Definition
Used for secretion. During high K levels, K leaks back into lumen using K leak channels and K, Cl symporter.
Secretion is highly dependent on negative charge in lumen, which in turn is dependent on flow.
If fluid is stationary, negative luminal voltage will go away, K will dissipate charge and K secretion will stop. If flow occurs, you are taking out high K fluid and bringing in new fluid, electrical gradient maintained and negative voltage persists, allows K secretion to continue. |
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Term
| Modulators of K secretion |
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Definition
Can be luminal or peritubular factors.
For luminal factors, an increased negative charge in the lumen will increase secretion. Things that dissipitate this negative charge, like secretion of K or reabsorption of Cl will inhibit further K secretion. HCO3- is impermeable, so it creates a permanent negative charge in the lumen that increases K secretion. |
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Term
| Hyperkalemia affects on K transport |
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Definition
Increased cellular uptake via Na, K-ATPase
Increased aldosterone = increased secretion:
Upregulation of Na, K-ATPase activity/pump# (increases # of pumps available)
Stimulated Na reabsorption
Increased apical membrane K permeability
Hypokalemia has opposite effect. |
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Term
| Glucocorticoid effect on K transport |
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Definition
Stimulate K excretion
Activate mineralocorticoid receptors
Increase GFR (increase filtered load of K) |
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Term
| Acidemia effects on K secretion |
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Definition
| Decreases secretion, lowered [Ki], inhibits Na, K-ATPase, lowers permeability of apical K channels |
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Term
| Alkalemia effects on K secretion |
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Definition
| Increases K secretion, increased [Ki], stimulates Na, K-ATPase, increases permeability of apical K channels |
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Term
| Epinephrine effect on K secretion |
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Definition
Decreased K secretion
Hypokalemia
Stimulates reabsorption in IMCD |
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Term
| Arginine Vasopressin effect on K secretion |
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Definition
| Mixed effects, lowers urine flow (decreases negative charge in tube which decreases K secretion), but increases permeability of K and Na. |
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