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Acid-Base Balance – 2nd Lab
1. Chemical Buffer Systems
a) Protein
b) Bicarbonate
c) Phosphate
2. Respiratory Adjustments
3. Renal Adjustments
Acid-Base Balance – 2nd Lab
pH of Arterial Blood
0
1
2
3
4
5
7
Normal
range
Acidosis
6.8
6
7.35
8
9
10
11
Alkalosis
7.45
7.8
12
13
14
1. Chemical Buffer Systems
Overall objective is to _____________________________________
They do not prevent pH changes.
A) The protein buffer system
e.g. Hb + H+  HHB
•
Intracellular proteins (esp. Hb) and plasma proteins can bind or
release H+ as necessary.
•
If more H+ are added... Many H+ will bind to proteins. Only a
portion remain free to affect pH.
•
If some H+ are removed... proteins will release some of their H+ to
replace some of them
•
Is the #1 buffer system you have. (accomplishes 75% of your
buffering)
•
Most influential in the ICF (inside cells) & (somewhat in plasma)
B) The Bicarbonate Buffer System
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Equilibrium exists: H2CO3 HCO3- + H+
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If add H+ ...?
Reaction would proceed _____________
# of free H+ would ____________
So pH would ___________
•
If add HCO3- ...?
Reaction would proceed ____________
# of free H+ would ___________
So pH would ____________
H2CO3  HCO3- + H+
•
•
If H+ are removed... ?
Reaction would proceed ___________________
# of free H+ _______________
pH would _____
If add H2CO3 ...?
Reaction would proceed ___________________
# of free H+ would ___________
pH would ______
•
The salt NaHCO3 found in body fluids and the HCO3- produced by the pancreas are the
sources of the HCO3-
•
Most influential in ECF outside cells. (somewhat in urine)
C) The Phosphate Buffer System
•
equilibrium
H2PO4-  HPO42- + H+
•
•
•
HPO42- = hydrogen phosphate anion
H2PO4- = dihydrogen phosphate anion
originally started as H3PO4 = phosphoric acid
•
•
•
If add more HPO42- …
If add more H2PO4- …
If add more H+ …
•
most influential in ICF inside cells & urine
2. RESPIRATORY ADJUSTMENTS
•
Based on your understanding of this equilibrium reaction occurring in
the blood:
H2CO3  H+ + HCO3CO2 + H2O  H2CO3  H+ + HCO3-
If muscles contraction ↑ then CO2 accumulates so [H+] would _______
•
And pH ________
•
And RR should _______
•
As ventilation increases, [CO2 ] should ________
•
… so reaction proceeds to the ________
•
And pH should ____.
At the tissues blood picks up _____
– So pH of venous blood is _______.
If decrease ventilation CO2 will ______ & reaction will proceed__________
Renal Adjustments
???
Reabsorption
???
Secretion
3. RENAL ADJUSTMENTS
•
•
•
•
•
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Recall Reabsorption… vs. Secretion…
Due to constant influx of H+ into our blood we usually trend toward _______
So what do the kidneys typically do with H+? ___________
Phosphates (HPO42-) already in the filtrate bind up many incoming free H+
Bicarb (HCO3-) also
“
“
“
but not as much
When secrete H+ we also reabsorb HCO3- (a coupled reaction. Fig 26.12)
– HCO3- reabsorbed to blood binds up H+ in blood
•
When reabsorb HCO3- also reabsorb Na+ (a coupled reaction)
•
Also tend to have a surplus of K+ in our blood so the kidneys should
___________ and Na+ is reabsorbed.
– could look at it as “trading” H+ or K+ for the Na+ (and HCO3-) you need
to reabsorb.
– Which one is secreted is determined by both H+ and K+ concentrations
of the blood.
Effect of aldosterone? …may not be what you think
Cont’d
•
•
NH3 is secreted to filtrate to buffer incoming H+
NH4+ (ammonium ion) may also be secreted from blood to get rid of H+
– This generates the formation of new HCO3- to be reabsorbed to
the blood.
Urine pH Values:
•
Normal Urine pH is ___________with extremes of ______ and _____
•
if <6 … your patient is (or recently was) in _________
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If >7… your patient is (or recently was) in _________
•
•
Buffers systems in the urine?
Phosphate is #1
Bicarb #2
Also NH3 binds with H+ in urine.
Priority goal of the kidneys is to control the pH of the blood rather than
the urine.
Summary
1. Chemical Buffer Systems
a) Protein
b) Bicarbonate
c) Phosphate
2. Respiratory Adjustments
↑↓CO2 and therefore ↑↓ H+
3. Renal Adjustments
↑↓ H+, HCO3-, NH3, K+