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93 Cards in this Set
- Front
- Back
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Arterial blood pH
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7.4
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Venous blood pH
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7.35
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ISF pH
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7.35
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ICF pH
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6 - 7.4
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Urine pH
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4.5 - 8
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Gastric acid pH
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0.8
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3 Defenses against changes in body fluid H ion concentration:
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1. Chemical buffer systems in body fluids
2. Respiratory system 3. Kidneys |
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3 chemical buffer systems in the body fluids:
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1. Bicarbonate
2. Phosphate 3. Protein |
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How soon do chemical buffer systems respond?
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Within seconds
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What can't chemical buffer systems do?
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Remove or add H+ from/to the body
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How soon does the respiratory system respond?
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Seconds - minutes
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What does the respiratory function do?
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Accelerates or slows down CO2 removal
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How soon do the kidneys respond?
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Few hours - days
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What can the kidneys do?
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Eliminate excess acid or base
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What defense mechanism against body acid/base changes is most powerful?
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The kidneys
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Which body chemical buffer system is most important?
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Bicarbonate
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Why do we use the pH system to talk about body acid/base?
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Because the actual amounts of acid/base in the body are SO tiny - nanomolar
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What is the normal concentration of H+ in the body?
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40 nM - 0.00004 mEq/L
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How do you calculate the normal pH?
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pH = -(log0.00000004) = 7.4
0.00004 mEq = 0.00000004 |
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What is the lower limit of pH at which a person can live more than a few hours?
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6.8
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What is the upper limit of pH at which a person can live more than a few hours?
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8.0
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Why is intracellular pH lower than plasma?
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B/c cell metabolism produces acid
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What is really the purpose of body chemical buffer systems?
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To tie up changes in acid/base until renal mechanisms can excrete excess or reabsorb more.
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What is a buffer defined as?
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A substance that can bind reversibly to H+ to minimize changes in concentrations of H+
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Why is it essential for the body to have chemical buffers?
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Because a huge amt of acid is produced by metabolism, and ingested, daily - w/out buffering, plasma pH would vary dramatically.
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What does the bicarbonate buffer system consist of?
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-Water
-H2CO3 -Na HCO3 -Carbonic anhydrase |
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What is the purpose of CA?
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To speed up the reaction which is slow otherwise.
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What are the 2 places where CA is present?
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-Lung alveoli walls
-Renal tubule epithelial cells -Renal brush border |
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What will excess acid react with? To form what?
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HCO3 - to form H2CO3
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What will excess base react with? To form what?
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H2CO3 - to form more HCO3
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How much H2CO3 is present in the blood for every mm of Hg of PCO2 measured?
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0.03 mmol
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What is 0.03 mmol called?
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The solubility coefficient for CO2
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What is the Henderson Hasselbach's equation?
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pH = pK + log (base)/(acidx.03)
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What system primarily controls ECF acid?
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Respiratory
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What system primarily controls ECF base?
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Kidneys
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What is a disturbance of acid/base balance caused by changes in ECF bicarb conc called?
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Metabolic Acid-base disturbance
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What is a disturbance caused by changes in respiration called?
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Respiratory acid-base disturbance
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What is pK?
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The concentration of acid/base at which a buffer's handling capacity is maximal.
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What happens when pH is AT the pK?
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The ratio of buffer in the form of Bicarb and CO2 = 1
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What happens when the pH is above the pK?
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-Less will be in the form of H2CO3 and CO2
-More will be in form of HCO3- |
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Within what pH range is the buffering power for bicarbonate buffer system highest?
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5.1 - 7.1
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So what is the buffering capacity of the bicarb system at physiological pH?
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Not very good
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What is the ratio of bicarb:CO2 at physiological pH?
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20:1
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Where is Phosphate most important as a buffer?
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-Renal tubular fluid
-Intracellular fluid |
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Where are proteins an important buffer?
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Intracellular
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One of the most important protein buffers inside cells:
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hemoglobin
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What makes proteins good buffers inside cells?
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-High concentration
-pKs close to physiologic pH |
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What is the normal body pH range?
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7.35 - 7.45
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What is the limit of pH range?
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6.8 - 7.8
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How much acid does a normal individual produce per day?
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15-20 moles/day
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Where does the majority of acid come from?
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Volatile CO2
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Where is the majority of acid removed?
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By the lungs
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What are the nonvolatile acids, and how are they removed?
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H2SO4 and HCL - removed by the kidneys
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How are the nonvolatile acids buffered?
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By sodium bicarb
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What does buffering of novolatile acids do?
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Depletes bicarb
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What is produced from the buffering of nonvolatile acids?
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Sodium salts (NaSO4)
CO2 Water |
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What has to be done to maintain acid/base balance after buffering of nonvolatile acids?
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-Excretion of excess acid
-Excretion of Na salts -Replenishment of HCO3 |
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How do the kidneys control acid/base balance?
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By excreting either an acidic or basic urine.
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How does the kidney handle acid and bicarb?
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-Filters alot of HCO3 and can either excrete or reabsorb it.
-Secretes alot of H+ from nonvolatile acids |
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What is the more imporant task of the kidneys in handling acid/base?
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Preventing loss of bicarb in the urine by reabsorbing almost all that is filtered.
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How much bicarb is filtered daily?
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4320 mEq/day
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What is the normal plasma bicarb concentration?
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24 mEq/l
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What must occur in order for 4320 mEq of HCO3 to be reabsorbed?
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4320 mEq of H+ have to be secreted!
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Why does acid have to be secreted in order for bicarb to be reabsorbed?
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Because bicarb doesn't readily permeate the apical membrane of renal tubules, so it has to be converted into H2O + CO2 via lumenal brush border CA
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How much acid has to be secreted for the body to get rid of nonvolatile acids?
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80 mEq
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How much total acid does the body secrete daily?
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4400 mEq/day
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So for Bicarb:
-How much is filtered daily -What % is reabsorbed in the Prox tubule, thick asc limb, and distal tubule? -How much excreted? |
Filtered: 4320 mEq/day
Reabs 85% in prox tubule Reabs 10% in thick asc limb Reabs <5% in distal tubule Excrete 1 mEq/day |
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How do kidney functions change during alkalotic conditions?
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They will fail to reabsorb all the bicarb, which is the same thing as adding acid to ECF.
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So what are the 3 fundamental mechanisms by which the kidneys regulate fluid H+ concentration?
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1. Secretion of H+
2. Reabsorption of filtered HCO3 3. Production of new HCO3 |
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What transporter is used for H+ secretion in the Prox tubule, Thick ascending limb, and Early Distal tubule?
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Na/H cotransporter
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What type of transport is the Na/H cotransporter?
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2ndary countertransport
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What creates the gradient for sodium to move from tubule lumen into tubule cell?
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Na/K ATPase on the basolateral membrane
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What supplies the energy for H+ to move up its gradient into the tubule lumen?
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Na moving down its gradient
Na/H countertransport |
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Where is there lumenal CA?
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only in the proximal tubule brush border.
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How does bicarb in the tubule cell get across the basolateral membrane?
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It diffuses via Na/HCO3 cotransport and Cl/HCO3 exchange.
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How is the little bit of excess acid from the body excreted?
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Via phosphate and ammonia urinary buffers
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How does acid secretion change at the LATE distal tubule?
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It becomes achieved by PRIMARY ACTIVE TRANSPORT
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What transporter achieves primary active transport of H+, and where is it?
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H+ transporting ATPase in the luminal membrane of late distal tubule intercalated cells (and beyond).
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What % of the total secreted H is done by this active transport mechanism?
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Only 5%
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Why do we care about this AT transport mechanism in the late distal tubule and collecting ducts?
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B/c that is the primary way that a maximally acidic urine is formed.
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How much can pee H+ concentrations be increased in:
-Proximal tubules? -Distal tubules? |
Proximal: 3-4X
Distal: 900X |
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What is the lower limit of pH that can be achieved in normal kidneys in the collecting ducts? In the proximal tubule?
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only down to about 6.5 = PT
all th way down to 4.5 = CD |
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How does the kidney excrete the 80 mEq excess of nonvolatile acid if it can only excrete a urine w/ pH as low as 4.5?
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By excreting them with buffers
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What are the most important urinary buffers?
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Ammonia and Sodium phosphate
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If one HCO3 is reabsorbed for every H+ secreted, what results from excess H+ being excreted via other buffers?
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New bicarb is generated!
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How does a new bicarb get made everytime a filtered NaHPO4 buffers an excess H+?
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Because everytime a secreted hydrogen gets transported to the lumen, it comes from the CA reaction, so a bicarb goes to the ISF/blood.
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Where does the excess acid come from?
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Eating meat which produces more CO2 from metabolism, which diffuses into tubule cells.
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Is the phosphate buffer system very important in buffering excess acid? Why/why not?
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No; because most filtered phosphate is reabsorbed and only a limited amt is available to buffer.
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What system is more important in buffering excess acid?
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Ammonia/Ammonium
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What is the source of ammonium ion?
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Glutamine from AA metabolism
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What happens when glutamate gets transported into tubule cells?
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It gets metabolized to produce
2 Bicarbs!! 2 Ammoniums |
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What is the fate of ammonium?
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It gets delivered to the tubule lumen via countertransport exchange for sodium.
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Where does Ammonium secretion occur?
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Everywhere except the thin limbs of LOH
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