Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
93 Cards in this Set
- Front
- Back
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
|