acid-base balance for allied health majors
DESCRIPTION
H 2 O + CO 2 H 2 CO 3 H + + HCO 3 -. HCO 3 -. α =0.03. pH = pK + log. pCO 2 ( α ). Acid-Base Balance for Allied Health Majors. Using the Henderson-Hasselbach Equation. Acid. An acid is a substance that will disassociate a H+ and become more negatively charged (electron acceptor). - PowerPoint PPT PresentationTRANSCRIPT
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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
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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
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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
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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
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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!!!!!
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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
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Bicarbonate: most important ECF buffer
H2O + CO2 H2CO3 H+ + HCO3 -CA
From metabolism Hydrogen is buffered by hemoglobin
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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
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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
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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.
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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
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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
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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)
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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
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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
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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)
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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
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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)
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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
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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?
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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?
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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?
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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?
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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
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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