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93 Cards in this Set

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Arterial blood pH
7.4
Venous blood pH
7.35
ISF pH
7.35
ICF pH
6 - 7.4
Urine pH
4.5 - 8
Gastric acid pH
0.8
3 Defenses against changes in body fluid H ion concentration:
1. Chemical buffer systems in body fluids
2. Respiratory system
3. Kidneys
3 chemical buffer systems in the body fluids:
1. Bicarbonate
2. Phosphate
3. Protein
How soon do chemical buffer systems respond?
Within seconds
What can't chemical buffer systems do?
Remove or add H+ from/to the body
How soon does the respiratory system respond?
Seconds - minutes
What does the respiratory function do?
Accelerates or slows down CO2 removal
How soon do the kidneys respond?
Few hours - days
What can the kidneys do?
Eliminate excess acid or base
What defense mechanism against body acid/base changes is most powerful?
The kidneys
Which body chemical buffer system is most important?
Bicarbonate
Why do we use the pH system to talk about body acid/base?
Because the actual amounts of acid/base in the body are SO tiny - nanomolar
What is the normal concentration of H+ in the body?
40 nM - 0.00004 mEq/L
How do you calculate the normal pH?
pH = -(log0.00000004) = 7.4


0.00004 mEq = 0.00000004
What is the lower limit of pH at which a person can live more than a few hours?
6.8
What is the upper limit of pH at which a person can live more than a few hours?
8.0
Why is intracellular pH lower than plasma?
B/c cell metabolism produces acid
What is really the purpose of body chemical buffer systems?
To tie up changes in acid/base until renal mechanisms can excrete excess or reabsorb more.
What is a buffer defined as?
A substance that can bind reversibly to H+ to minimize changes in concentrations of H+
Why is it essential for the body to have chemical buffers?
Because a huge amt of acid is produced by metabolism, and ingested, daily - w/out buffering, plasma pH would vary dramatically.
What does the bicarbonate buffer system consist of?
-Water
-H2CO3
-Na HCO3
-Carbonic anhydrase
What is the purpose of CA?
To speed up the reaction which is slow otherwise.
What are the 2 places where CA is present?
-Lung alveoli walls
-Renal tubule epithelial cells
-Renal brush border
What will excess acid react with? To form what?
HCO3 - to form H2CO3
What will excess base react with? To form what?
H2CO3 - to form more HCO3
How much H2CO3 is present in the blood for every mm of Hg of PCO2 measured?
0.03 mmol
What is 0.03 mmol called?
The solubility coefficient for CO2
What is the Henderson Hasselbach's equation?
pH = pK + log (base)/(acidx.03)
What system primarily controls ECF acid?
Respiratory
What system primarily controls ECF base?
Kidneys
What is a disturbance of acid/base balance caused by changes in ECF bicarb conc called?
Metabolic Acid-base disturbance
What is a disturbance caused by changes in respiration called?
Respiratory acid-base disturbance
What is pK?
The concentration of acid/base at which a buffer's handling capacity is maximal.
What happens when pH is AT the pK?
The ratio of buffer in the form of Bicarb and CO2 = 1
What happens when the pH is above the pK?
-Less will be in the form of H2CO3 and CO2
-More will be in form of HCO3-
Within what pH range is the buffering power for bicarbonate buffer system highest?
5.1 - 7.1
So what is the buffering capacity of the bicarb system at physiological pH?
Not very good
What is the ratio of bicarb:CO2 at physiological pH?
20:1
Where is Phosphate most important as a buffer?
-Renal tubular fluid
-Intracellular fluid
Where are proteins an important buffer?
Intracellular
One of the most important protein buffers inside cells:
hemoglobin
What makes proteins good buffers inside cells?
-High concentration
-pKs close to physiologic pH
What is the normal body pH range?
7.35 - 7.45
What is the limit of pH range?
6.8 - 7.8
How much acid does a normal individual produce per day?
15-20 moles/day
Where does the majority of acid come from?
Volatile CO2
Where is the majority of acid removed?
By the lungs
What are the nonvolatile acids, and how are they removed?
H2SO4 and HCL - removed by the kidneys
How are the nonvolatile acids buffered?
By sodium bicarb
What does buffering of novolatile acids do?
Depletes bicarb
What is produced from the buffering of nonvolatile acids?
Sodium salts (NaSO4)
CO2
Water
What has to be done to maintain acid/base balance after buffering of nonvolatile acids?
-Excretion of excess acid
-Excretion of Na salts
-Replenishment of HCO3
How do the kidneys control acid/base balance?
By excreting either an acidic or basic urine.
How does the kidney handle acid and bicarb?
-Filters alot of HCO3 and can either excrete or reabsorb it.
-Secretes alot of H+ from nonvolatile acids
What is the more imporant task of the kidneys in handling acid/base?
Preventing loss of bicarb in the urine by reabsorbing almost all that is filtered.
How much bicarb is filtered daily?
4320 mEq/day
What is the normal plasma bicarb concentration?
24 mEq/l
What must occur in order for 4320 mEq of HCO3 to be reabsorbed?
4320 mEq of H+ have to be secreted!
Why does acid have to be secreted in order for bicarb to be reabsorbed?
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
How much acid has to be secreted for the body to get rid of nonvolatile acids?
80 mEq
How much total acid does the body secrete daily?
4400 mEq/day
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
How do kidney functions change during alkalotic conditions?
They will fail to reabsorb all the bicarb, which is the same thing as adding acid to ECF.
So what are the 3 fundamental mechanisms by which the kidneys regulate fluid H+ concentration?
1. Secretion of H+
2. Reabsorption of filtered HCO3
3. Production of new HCO3
What transporter is used for H+ secretion in the Prox tubule, Thick ascending limb, and Early Distal tubule?
Na/H cotransporter
What type of transport is the Na/H cotransporter?
2ndary countertransport
What creates the gradient for sodium to move from tubule lumen into tubule cell?
Na/K ATPase on the basolateral membrane
What supplies the energy for H+ to move up its gradient into the tubule lumen?
Na moving down its gradient
Na/H countertransport
Where is there lumenal CA?
only in the proximal tubule brush border.
How does bicarb in the tubule cell get across the basolateral membrane?
It diffuses via Na/HCO3 cotransport and Cl/HCO3 exchange.
How is the little bit of excess acid from the body excreted?
Via phosphate and ammonia urinary buffers
How does acid secretion change at the LATE distal tubule?
It becomes achieved by PRIMARY ACTIVE TRANSPORT
What transporter achieves primary active transport of H+, and where is it?
H+ transporting ATPase in the luminal membrane of late distal tubule intercalated cells (and beyond).
What % of the total secreted H is done by this active transport mechanism?
Only 5%
Why do we care about this AT transport mechanism in the late distal tubule and collecting ducts?
B/c that is the primary way that a maximally acidic urine is formed.
How much can pee H+ concentrations be increased in:
-Proximal tubules?
-Distal tubules?
Proximal: 3-4X
Distal: 900X
What is the lower limit of pH that can be achieved in normal kidneys in the collecting ducts? In the proximal tubule?
only down to about 6.5 = PT

all th way down to 4.5 = CD
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?
By excreting them with buffers
What are the most important urinary buffers?
Ammonia and Sodium phosphate
If one HCO3 is reabsorbed for every H+ secreted, what results from excess H+ being excreted via other buffers?
New bicarb is generated!
How does a new bicarb get made everytime a filtered NaHPO4 buffers an excess H+?
Because everytime a secreted hydrogen gets transported to the lumen, it comes from the CA reaction, so a bicarb goes to the ISF/blood.
Where does the excess acid come from?
Eating meat which produces more CO2 from metabolism, which diffuses into tubule cells.
Is the phosphate buffer system very important in buffering excess acid? Why/why not?
No; because most filtered phosphate is reabsorbed and only a limited amt is available to buffer.
What system is more important in buffering excess acid?
Ammonia/Ammonium
What is the source of ammonium ion?
Glutamine from AA metabolism
What happens when glutamate gets transported into tubule cells?
It gets metabolized to produce
2 Bicarbs!!
2 Ammoniums
What is the fate of ammonium?
It gets delivered to the tubule lumen via countertransport exchange for sodium.
Where does Ammonium secretion occur?
Everywhere except the thin limbs of LOH