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Acid-Base Balance for Allied Health Majors
Using the Henderson-Hasselbach Equation
H2O + CO2 H2CO3 H+ + HCO3 -
pH = pK + logHCO3 -
pCO2 (α)α =0.03
Acid• An acid is a substance that will disassociate a H+ and
become more negatively charged (electron acceptor).• When hydrogen ions accumulate in a solution, it
becomes more acidic ([H+] increases = more acidity).
72
pH
HCl
H + Cl-
H + Cl-
H + Cl-
H + Cl-
H + Cl-
Hydronium ions in solutionConcentration of hydrogen ions increases, pH drops
Base• A base is chemical that will remove hydrogen ions from
the solution• the base has a negative charge (or extra electrons) to
donate to hydrogen ions and thus create a bond with hydrogen
72
pH
H + Cl-
H + Cl-
H + Cl-
H + Cl-
H + Cl-NaOH Na+ OH-
Na+ OH-
Na+ OH-
Na+ OH-
Acids and basis neutralize eachother
72
pHNa+ Cl-
Na+ Cl-
Na+ Cl-Na+ Cl-
H+ OH- H2O
pH log[H] log1
H
A change of 1 pH unit corresponds to a 10-fold change in hydrogen ion concentration
Acids are being created constantly through metabolism
• Inorganic phosphates (mostly from ATP, etc.)
• Anaerobic respiration of glucose produces lactic acid
• Fat metabolism yields organic acids and ketone bodies
• Carbon dioxide!!!!!
Acids must be buffered, transported away from cells, and eliminated from the body
Phosphate: important renal tubular bufferHPO4
- + H+ H2PO 4
Ammonia: important renal tubular bufferNH3 + H+ NH4
+
Proteins: important intracellular and plasma buffersH+ + Hb HHb Histidine in proteins
is particularly good at neutralizing hydrogen ions
Bicarbonate: most important ECF buffer
H2O + CO2 H2CO3 H+ + HCO3 -CA
From metabolism Hydrogen is buffered by hemoglobin
Buffering is good, but it is a temporary solution. Excess acids and bases must be
eliminated from the body
H2O + CO2 H2CO3 H+ + HCO3 -CA
Lungs eliminate carbon dioxide
Kidneys can remove excess non-volatile acids and bases
gas aqueous
Excessive Acids and Bases can cause pH changes---denature proteins
• Normal pH of body fluids is 7.40• Alkalosis or alkalemia – arterial blood pH rises above
7.45• Acidosis or acidemia – arterial pH drops below 7.35
(physiological acidosis)• For our class, we will stick to 7.40 as normal!
• Acidosis: – too much acid– Too little base
• Alkalosis– Too much base– Too little acid
Compensation for deviation• Lungs (only if not a respiratory problem)
– If too much acid (low pH)—respiratory system will ventilate more (remove CO2) and this will raise pH back toward set point
– If too little acid (high pH)—respiratory will ventilate less (trap CO2 in body) and this will lower pH back toward set point
• Kidneys– If too much acid (low pH)—intercalated cells
will secrete more acid into tubular lumen and make NEW bicarbonate (more base) and raise pH back to set point.
– If too little acid/excessive base (high pH)- proximal convoluted cells will NOT reabsorb filtered bicarbonate (base) and will eliminate it from the body to lower pH back toward normal.
How would your ventilation change if you
had excessive acid?
[H+]AlveolarVentilation
pCO2
H2O + CO2 H2CO3 H+ + HCO3 -
This is too high and this means the buffer system swings this way!
CO2 vented out
How would your ventilation change if you
had too little acid?
[H+]AlveolarVentilation
pCO2
H2O + CO2 H2CO3 H+ + HCO3 -
This is too low and this means the buffer system swings this way!
CO2 trapped
How can the kidneys control acids and bases?
• Bicarbonate is filtered and enters nephron at Bowman’s capsule
• Proximal convoluted tubule– Can reabsorb all
bicarbonate (say, when you need it to neutralize excessive acids in body)
OR
– Can reabsorb some or NONE of the bicarbonate (maybe you have too much base in body and it needs to be eliminated)
How can the kidneys control acids and bases?
• Acidosis• Intercalated cells
– Secrete excessive hydrogen
– Secreted hydrogen binds to tubular buffers (ammonia and phosphate bases)
– Secretion of hydrogen leads to gain of bicarbonate (NEW!)
HPO4-
NH3
What would happen if the respiratory system had a problem with ventilation?
Respiratory Acidosis and Alkalosis
PCO2 levels-Normal PCO2 fluctuates between 35 and 45 mmHg
• Respiratory Acidosis (elevated CO2 greater than 45mmHg)
• Depression of respiratory centers via narcotic, drugs, anesthetics
• CNS disease and depression, trauma (brain damage)
• Interference with respiratory muscles by disease, drugs, toxins
• Restrictive, obstructive lung disease (pneumonia, emphysema)
• Respiratory Alkalosis (less than 35mmHg- lowered CO2)
• Hyperventilation syndrome/ psychological (fear, pain)
• Overventilation on mechanical respirator
• Ascent to high altitudes• Fever
What if your metabolism changed? • Metabolic acidosis • bicarbonate ion
levels below normal (22 mEq/L)
• Metabolic alkalosis• bicarbonate ion levels higher
(greater than 26mEq/L)
• Ingestion, infusion or production of more acids (alcohol)
• Carbonic anhydrase inhibitors (decreased H+ secretion)
• Salicylate overdose (aspirin)
• Diarrhea (loss of intestinal HCO3
-)• Accumulation of lactic
acid in severe Diabetic ketoacidosis
• starvation
• Excessive loss of fixed acids due to ingestion, infusion, or renal reabsorption of bases
• Loss of gastric juice during vomiting
• Intake of stomach antacids (Leisure world syndrome)
• Diuretic abuse (loss of H+ ions)
• Severe potassium depletion (increased aldosterone)
• Steroid therapy (mineralcorticoid excess)
H2O + CO2 H2CO3 H+ + HCO3 -
pH = pK + logHCO3 -
pCO2
(α)Acidosis: pH < 7.4
- metabolic: HCO3 -
- respiratory: pCO2
Alkalosis: pH > 7.4- metabolic: HCO3 -
- respiratory: pCO2
Mechanisms of Acidosis and Alkalosis
α =0.03
Compensation
Acidosis (pH<7.40)
Alkalosis
(pH >7.40)
Problem Compensation
Too much acid (High CO2)
Too little acid (low CO2)
Respiratory Kidneys
Too little base
(low HCO3-)
Too much base
(high HCO3-)
Metabolic Respiratory (quick!)
Kidneys
(long-term)
Analysis of Simple Acid-Base Disorders
Figure 30-10; Guyton and Hall
Step One:
Step 3
Step Two
<22 >26
>26 <22
<35
<35 >45
>45
Resp and renal compensation
Resp and renal compensation
Let’s practice
What is the problem?: pH pCO2 HCO3-
PCO2 complete HCO3- reabs.
+excess tubular H+
H+ secretion
pH Buffers (NH4+, NaHPO4
-)
H+ +new HCO3
-
Buffers -
H2O + CO2 H2CO3 H+ + HCO3 -
What is the correction and which organ system does this?
What is the problem?: pH pCO2 HCO3-
PCO2 H+ secretion
pH
HCO3- reabs.
+excess tubular HCO3
-
HCO3
-
+ H+ excretion
excretion
Let’s practice
What is the correction and which organ system does this?
H+
What is the problem?: pH pCO2 HCO3-
HCO3- complete HCO3
- reabs. +excess tubular H+
pH
HCO3-
filtration
+new HCO3
-
Buffers -
Buffers (NH4+, NaHPO4-)
What is the respiratory system doing at the same time?
Let’s practice
What is the correction and which organ system does this?
pH pCO2 HCO3-
HCO3-
pH
HCO3-
filtration
HCO3- reabs.
excess tubular HCO3-
excretion
H+ excretion
HCO3-
+
Let’s practice
What is the problem?:
What is the correction and which organ system does this?
What is the respiratory system doing at the same time?
Anion Gap-- protein , phosphate, citrate, sulfate
Na+Cl-
Aniongap
HCO3-
Meta. acidosis: too little baseMore Cl- and anion gap sameDiarrhea, renal acidosis
Meta. acidosis: too little baseMore Cl- and anion gap biggerKetoacidosis, salicylate, lactateChronic renal failure
Na+ Cl-
Aniongap
HCO3-
Na+Cl-
Aniongap
HCO3-
electroneutrality
Overuse of Diuretics
Metabolic Alkalosis
K+ depletionangiotensin II
aldosterone
extracell. volume
tubular H+ secretion
HCO3 reabsorption+ new HCO3 Production
Clinical Correlation: Abuse of Diuretics or Conn’s disease
Conn’s disease