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Buffer systems
RESPONSES TO:
ACIDOSIS AND ALKALOSIS
Mechanisms which protect the body against
life-threatening changes in hydrogen ion
concentration:
1) Buffering Systems in Body Fluids
2) Respiratory Responses
3) Renal Responses
4) Intracellular Shifts of Ions
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1) Buffering systems in body fluids provide an
immediate response to fluctuations in pH
1) Phosphate
2) Protein
3) Bicarbonate Buffer System
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Chemical buffers are able to react
immediately (within milliseconds).
Chemical buffers are the first line
of defense for the body for
fluctuations in pH.
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1) Phosphate buffer system
Na2HPO4 + H+
NaH2PO4 + Na+
Most important in the intracellular system
Phosphate concentrations are higher
intracellularly and within the kidney tubules.
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2) Protein Buffer System
Behaves as a buffer in both plasma and cells.
Most important intracellular buffer (ICF).
The most plentiful buffer of the body.
Hemoglobin is by far the most important
protein buffer.
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3) Bicarbonate Buffer System
Predominates in extracellular fluid (ECF)
HCO3- + added H+
H2CO3
This system is most important because the
concentration of both components can be regulated:
Carbonic acid by the respiratory system
Bicarbonate by the renal system
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2) Respiratory Responses
Overall compensatory response is:
Hyperventilation in response to increased
CO2 or H+ (low pH).
Hypoventilation in response to decreased
CO2 or H+ (high pH).
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RESPIRATORY CONTROL OF pH
cell production of CO2 increases
CO2 + H2O
H2CO3
H2CO3
H+ + HCO3H+
acidosis; pH drops
H+ stimulates respiratory center in medulla oblongata
rate and depth of breathing increase
CO2 eliminated in lungs
pH rises toward normal
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3) RENAL RESPONSE
The kidney compensates for Acid - Base imbalance
within 24 hours and is responsible for long term
control.
The kidney in response:
To Acidosis
Retains bicarbonate ions and eliminates
hydrogen ions.
To Alkalosis
Eliminates bicarbonate ions and retains
hydrogen ions.
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Mechanism of HCO3- Reabsorption and
Na+ - H+ Exchange
H+ secretion in Distal & Collecting Tubule
H+ secretion and excretion couples with addition of
HCO3 to plasma
Control of rate of tubular secretion & H+
reabsorption
Other Urinary Buffers
 The minimal urine pH is about 4.5
 In order to excrete more H+, the acid must be
buffered in tubular lumen.
 H+ secreted into the tubule combines with HPO4-2
or NH3.
 HPO4-2 + H+
 NH3 + H+
H2PO4-2
NH4+
Buffering of Secreted H+ by Filtered phosphate
(NaHPO4-) and Generation of “New” HCO3-
“New” HCO3-
Glutamine is the most abundant free amino
acid that:
1- Help in protein synthesis.
2- regulate acid –base balance in the kidney
by producing ammonium.
During metabolic acidosis, the kidney
becomes the major site for glutamine
extraction and catabolism.
Production and Secretion of NH4+ and HCO3- by Proximal,
Thick Loop of Henle, and Distal Tubules
H++NH3
“New” HCO3-
4) Intracellular Shifts of Ions
Hyperkalemia
Is generally associated with acidosis.
Accompanied by a shift of H+ ions into cells and K+
ions out of the cell to maintain electrical neutrality.
Hypokalemia
Is generally associated with reciprocal exchanges
of H+ and K+ in the opposite direction.
Associated with alkalosis.
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ELECTROLYTE SHIFTS
Acidosis
Compensatory Response
H+
K+
Result
- H+ buffered intracellularly
- Hyperkalemia
cell
Alkalosis
Compensatory Response
H+
K+
cell
Result
- Tendency to correct alkalosis
- Hypokalemia
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Summary of acid base abnormalities