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45 Cards in this Set
- Front
- Back
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What is the most abundant intracellular ion?
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Potassium
98% intracellular fluid 2% extracellular fluid |
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What is the [K+] in the extracellular fluid important for?
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Function of excitable tissues (nerve and muscle)
-> cuz the resting mb potentials of these tissues are directly related to the relativeintra and extracell concentrations of K+ |
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What is hyperkalemia?
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High [K+] in extracellular flui (>5mEq/L)
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What is hypokalemia?
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low [K+] in extracellular fluid (<3.5mEq/L)
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What can both of these cause?
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Abnormal rhythms of the heart
Abnormalities oof skeletal muscle contraction |
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What effect does hyperkalemia have on the electrocardiogram?
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Pre-cardiac arrest
At K=8.0 harder to contract, get elongation of the wave |
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Which organ maintains potassium balance?
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Kidney
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Where does K+ come from?
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Dietary intake
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How is K+ excreted?
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90%: in urine
10% in feces/sweat |
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Is K+ freely filtered at the glomerulus?
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yes
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What happens to most of the filtered K+?
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Reabsorbed by the tubules
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What makes K+ dif from Na and wate?
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K+ can be secreted at the CCD
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What are changes in K+ secretion due to?
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Changes in K+ secretion in the CCD (and also in the DCT)
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What is the normal reabsorption of K+?
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~86%
(can range from 15-99%) |
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What is secretion of K+ in the CCD coupled with?
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Na+ reabsorption
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What regulates K+ secretion?
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1) Dietary intake
2) Aldosterone |
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What does aldosterone do?
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Simulates K+ secretion
Retain/absorb Na+ |
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Describe the regulation of K+ by dietary intake and aldosterone.
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Inc K+ intake
-Inc plasma K+ (direct impact on adrenal cortex and CCD) -Adrenal cortex: inc aldosterone secretion -Inc plasma aldosterone -CCD: inc K+ secretion -Inc K+ secretion |
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Can K+ excretion occur when the renin-aldosterone system is activated by other causes?
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Yes (has ore nor less the same end result)
dec plasma vol -inc in plasma AG II -Inc aldosterone secretion in the adrenal cortex -Inc plasma aldosterone -CCD: inc Na reabsorption and Inc K+ excretion (can lead to hypokalemia) |
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What is hyperaldosteronism?
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Conditions under which aldosterone (adrenal cortex H) is in excess
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What is the most common cause of hyperaldosteronim?
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Adenoma of the adrenal gland that produces aldosterone autonomously (get a bening tumour in cells that produce aldosterone)
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What is the effect of hyperaldosteronism?
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Increased fluid volume ( Na retention)
Hypertension Hypokalemia (because inc aldosterone leads to inc K+ SECRETION) Renin suppressed Can get metabolic alkalosis |
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Why is the H+ ion concentration highly regulated?
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Metabolic reactions are highly sensitive to the H+ ion concentration of the environment
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What is the pH of the body?
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7.4
[H+]= ~40nmol/L Range of pH to live: [6.8 - 8.0) |
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What is the important reaction involving H+?
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CO2 + H2O <--> H2CO3 <--> HCO3- + H+
-when a molec of bicarbonate is lost, it's like gaining an H+ -when a bicarbonate ion is gaines,it's like losing an H+ ion |
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What are the sources of H+ gain?
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1) Generation of H+ ions from CO2 (volatile acid)
2) Production of nonvolatile acids from the metabolism of protein and other organic molecules (not H2CO3) 3) Gain of H+ ions due to the loss of HCO3- in diarrhea and other nongastric GI fluids 4) Gain of H+ ions due to the loss of bicarbonate in the urine #3 and 4 only occur in pathological diseases |
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What are the sources of H+ loss?
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1) Hyperventialtion (Loss of CO2)
2) Utilization of H+ ions in the metabolism of various organic anions 3) Loss of H+ ions in vomitus 4) Loss of H+ ions in the urine |
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What are examples of nonvolatile acids?
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Phosphoric acids
Sulfuric Acid Lactic acid ->Avg net production of 40-80mmol of H+/day (the H+ concentration, however, is kept at 40nmol/day (nanoM)) .: need to neutralize this production of acid |
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What is a buffer?
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Any substance that can reversibly bind H+ ions
Buffer- + H+ <-->Hbuffer ->without buffering, H+ ion concentations would change a lot, would alter the pH so much that we would die |
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What is a major extracellular buffer?
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CO2/HCO3- system
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What are major intracellular buffers?
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Phosphates
Proteins |
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Does buffereing eliminate H+ ions?
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No, jsut keeps them temporarily occupied/locked up
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What is the ultimate balance of hydrogen ion controled by?
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Respiratory system (controls CO2)
Kidneys (controls HCO3-) ->both these systems work together to minimize the change of [H+] (pH) |
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What happens to HCO3 when the cells have low [H+]?
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low H+: high pH (alkalosis)
Kidneys excrete HCO3- |
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What happens to HCO3- if there is a high [H+]?
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high H+ = low pH (acidosis)
Kidneys produce new HCO3- and add to the plasma (+ retain the HCO3- that is already present) |
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What ration determines the body pH?
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HCO3/CO2
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What does HCO3- excretion equal?
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HCO3- excretion = HCO3- filtered (+HCO3- secreted) - HCO3- reabsorbed
(HCO3- secreted is generally very small) |
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What happens to the filtered HCO3- under normal conditions? What is the exception?
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Its all reabsorbed by the kidneys
Exception: When there is already too much HCO3- (alkalosis), the kidneys don't reabsorb all the bicarbonate |
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What mediates H+ transport?
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H+/K+ ATPase
Na+/H+ antiporter |
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Where does HCO3- reabsorption take place?
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Mostly in the proximal tubule
Some in the TAL A bit in the CCD |
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How can new HCO3- be added to the plasma?
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1) H+ secretion and excretion on non-bicarbonate buffers (i.e phospate) into the unire
2) Glutamine metabolism with NH4+ excretion ->both processes like H+ excretion by the kidney because H+ goes onto the urine side and HCO3- goes onto the blood site |
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When does buffering by H-PO4 happen?
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After all the HCO3- has been reabsorbed and is no longer available in the urine
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What happens in the H-PO4 buffereing system?
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Same initial rxn:
HCO3 oes back into circulation via ISF H+ secreted to tubular lumen ->Dif: accepor of H+ is HPO4 End result: Addition of 1 new HCO3 to the blood (elimination of 1 H+) |
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Where does the glutamine metabolism take place?
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Mostly in proximal tubule
Glutamin goes from tubular lumen to tubular epithelial cells (active transport of aa, using Na+) -In epithelial cells, glutamine releases NH4+ and HCO3- -HCO3- diffuses out of cell into ISF and back onto circulation NH4+ actively taken into lumen ->Excretion of H+ cuz the H+ leave with NH3+ as NH4+ and is excreted in the urine |
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How much new HCO3- can the kidneys contribute?
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Enough to compensate fot the H+ ions from nonvolatile acids generated innthe body (40-80mmol/day)
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