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Questions and Answers
How do the respiratory and renal mechanisms help compensate for alkalosis and acidosis?
How do the respiratory and renal mechanisms help compensate for alkalosis and acidosis?
What is the role of buffer systems in the human body?
What is the role of buffer systems in the human body?
In uncompensated respiratory acidosis, what is the main change in arterial blood gases?
In uncompensated respiratory acidosis, what is the main change in arterial blood gases?
Of the following, what is the likely cause of a patient with pH 7.25, PaCO2 25, PaO2 62, HCO3- 15?
Of the following, what is the likely cause of a patient with pH 7.25, PaCO2 25, PaO2 62, HCO3- 15?
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What is the most important acid-base buffer system in the blood?
What is the most important acid-base buffer system in the blood?
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Which of the following is NOT a major acid in fixed acids removed by the kidneys?
Which of the following is NOT a major acid in fixed acids removed by the kidneys?
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How does the respiratory system control CO2 levels in the body?
How does the respiratory system control CO2 levels in the body?
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Which buffer system is the major buffer of interstitial fluid?
Which buffer system is the major buffer of interstitial fluid?
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What type of rapid response occurs when there is an increase in arterial [H+] due to ketoacidosis?
What type of rapid response occurs when there is an increase in arterial [H+] due to ketoacidosis?
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How does the bone salts of hydroxyapatite contribute to acid-base balance?
How does the bone salts of hydroxyapatite contribute to acid-base balance?
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What is the role of the respiratory system in acid-base regulation?
What is the role of the respiratory system in acid-base regulation?
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How is pH related to the concentration of hydrogen ions in a solution?
How is pH related to the concentration of hydrogen ions in a solution?
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Which system resists pH changes by removing volatile acids?
Which system resists pH changes by removing volatile acids?
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What is the pH of gastric acid in the body?
What is the pH of gastric acid in the body?
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Which buffer system is weaker than the bicarbonate system?
Which buffer system is weaker than the bicarbonate system?
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Which of the following DOES NOT cause respiratory alkalosis?
Which of the following DOES NOT cause respiratory alkalosis?
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Which condition results in metabolic acidosis?
Which condition results in metabolic acidosis?
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What happens to blood pH during respiratory alkalosis?
What happens to blood pH during respiratory alkalosis?
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How does the respiratory system assist in regulating pH?
How does the respiratory system assist in regulating pH?
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What causes metabolic acidosis?
What causes metabolic acidosis?
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What is one cause of respiratory alkalosis?
What is one cause of respiratory alkalosis?
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Metabolic alkalosis can be caused by excessive renal reabsorption of bases.
Metabolic alkalosis can be caused by excessive renal reabsorption of bases.
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Anion gap acidosis can result from an increased plasma concentration of anions other than chloride and bicarbonate.
Anion gap acidosis can result from an increased plasma concentration of anions other than chloride and bicarbonate.
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Metabolic alkalosis can result from the loss of hydrogen ions.
Metabolic alkalosis can result from the loss of hydrogen ions.
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Non-gap acidosis is commonly treated with sodium chloride (NaCl).
Non-gap acidosis is commonly treated with sodium chloride (NaCl).
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Respiratory compensation in acidosis involves a decrease in minute ventilation.
Respiratory compensation in acidosis involves a decrease in minute ventilation.
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In the context of hypoxemia, what is the main cause of anemic hypoxia?
In the context of hypoxemia, what is the main cause of anemic hypoxia?
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Which condition involves toxic agents preventing cellular utilization of oxygen, as described in the text?
Which condition involves toxic agents preventing cellular utilization of oxygen, as described in the text?
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What is the consequence of a left shift in P50 as mentioned in the text?
What is the consequence of a left shift in P50 as mentioned in the text?
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How does acetazolamide contribute to acid-base balance, as outlined in the text?
How does acetazolamide contribute to acid-base balance, as outlined in the text?
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Study Notes
Acid-Base Balance
- Acid-Base Balance is crucial for homeostasis
- pH regulation is important since most biochemical reactions are pH dependent
Chemistry of Acids, Bases, and Buffers
- Acid: a molecule that releases a hydrogen ion (proton) in solution
- Base: a molecule that can accept a hydrogen ion in solution; a strong base
- Strong acid: completely dissociates
- Weak acid: has a strong conjugate base
- Sources of acids in the body: cellular metabolism
- CO2 formed by metabolism is hydrated to H2CO3, resulting in a large total H+ load
- Most CO2 excreted by lungs
- Small remaining quantities of H+ excreted by kidneys
pH Regulation
- pH is a measure of the [H+] in a solution
- pH = - log [H+]
- Increase [H+] decreases pH
- Decrease [H+] increases pH
- Body attempts to regulate blood pH to 7.40
- Normal pH = 7.35-7.45
- pH limits under pathologic conditions = 6.9- 7.8
- Acidosis/acidemia occurs at a pH < 7.35
- Alkalosis/alkalemia occurs at a pH > 7.45
Buffer Systems of the Body
- Three mechanisms that resist pH changes are:
- Lungs remove volatile acids (~20,000 mmol CO2/day)
- Kidneys remove fixed acids (~ 100 mEq/day)
- Buffers reversibly bind hydrogen ions to minimize changes in H+ concentration/ pH
- Three major acid-base buffer systems in the blood:
- Carbonic acid- Bicarbonate System (most important)
- Proteins (mainly hemoglobin) (second most important)
- Phosphate (glucose-1-phosphate and ATP)
- Additional buffers:
- Bicarbonate buffer system is the major buffer of interstitial fluid
- Bone salts of hydroxyapatite can buffer H+ ions in chronic acidosis
Respiratory Control of Acid-Base Balance
- Respiratory system controls:
- CO2 directly by altering ventilation to change PaCO2 (volatile acid)
- [H+1] indirectly by controlling CO2/H2CO3 via the carbonic acid reaction
- Respiratory correction of imbalance occurs within minutes
- Incomplete correction since the original source of H+ hasn't been eliminated
Renal Regulation of Acid-Base Balance
- Renal regulation occurs by altering the excretion of fixed acids and HCO3 retention
- Renal compensation for acidosis occurs by:
- Increased H+ secretion into the tubular fluid
- Decreased HCO3- reabsorption
- Compensation for acid-base imbalances takes hours to days
- Powerful - can completely compensate for acid-base imbalances
- Returns ECF pH to normal
Acid-Base Abnormalities
- Acid-base abnormalities produce changes in pH, PCO2, and plasma bicarbonate
- Primary problems:
- Respiratory acidosis
- Respiratory alkalosis
- Metabolic acidosis
- Metabolic alkalosis
- Compensation:
- Respiratory acidosis: metabolic compensation (kidneys excrete H+ ions/conserve HCO3)
- Respiratory alkalosis: metabolic compensation (kidneys excrete HCO3-)
- Metabolic acidosis: respiratory compensation (increased alveolar ventilation)
- Metabolic alkalosis: respiratory compensation (decreased alveolar ventilation)
Anion Gap
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Acidosis with a large anion gap indicates an increased plasma concentration of anions other than chloride and bicarbonate or a decreased plasma concentration of K+, Ca++, and Mg++
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Anion gap = Major cations - Major anions = 8-12 mEq/L
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Anion gap >14 mEq/L = Anion gap acidosis
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Anion gap < 14 mEq/L = Non-anion gap acidosis
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Treat underlying cause### Acid-Base Balance
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Some CO2 is not buffered in the plasma, producing small amounts of H+ ions in venous blood, making it slightly more acidic (pH 7.35) compared to arterial blood (pH 7.4)
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The phosphate buffer system has two components: dihydrogen phosphate (H2PO4-) and monophosphate (HPO4-2), but it is weaker than the bicarbonate system and has smaller amounts of components
Respiratory Regulation of Acid-Base Balance
- The respiratory system assists in regulating pH by controlling PaCO2, as tissues constantly produce CO2, equivalent to an acid
- Hyperventilation causes respiratory alkalosis, resulting in an increase in blood pH due to a loss of CO2
- Hypoventilation causes respiratory acidosis, resulting in a decrease in blood pH due to an increase in [H+1]
Acid-Base Abnormalities
- Acid-base abnormalities produce changes in pH, PCO2, and plasma bicarbonate
- Normal values:
- pH: 7.35-7.45
- PaCO2: 35-45 mmHg
- HCO3-: 22-26 mEq/L
- Compensation:
- Full compensation restores pH to normal value
- Partial compensation moves pH towards normal, but pH remains abnormal
- Mixed disorders are possible (e.g., type 1 diabetes with respiratory failure)
Respiratory Acidosis
- Caused by impaired alveolar ventilation, resulting in increased CO2 production or decreased CO2 elimination
- Consequences:
- Increased respiratory rate and effort
- Cardiac output increases to compensate for acidosis
- Kidney excretes H+ ions and conserves HCO3-
- Metabolic compensation takes hours to days
Respiratory Alkalosis
- Caused by alveolar ventilation exceeding CO2 production, resulting in decreased PaCO2
- Consequences:
- Decreased respiratory rate and effort
- Cardiac output decreases to compensate for alkalosis
- Kidney excretes HCO3-
- Metabolic compensation occurs quickly, but may take longer to reverse
Metabolic Acidosis
- Caused by ingestion, infusion, overproduction, or decreased renal excretion of H+ ions, or loss of bicarbonate ions
- Causes:
- Increased HCO3 loss
- Gain of nonvolatile acid
- Increased mineralocorticoid
- Respiratory compensation: decreased alveolar ventilation, increasing PaCO2
- Treatment: treat underlying cause, acetazolamide increases renal excretion of HCO3, spironolactone is a mineralocorticoid antagonist, and dialysis
Metabolic Alkalosis
- Caused by ingestion, infusion, overproduction, or increased renal retention of HCO3-, or loss of H+ ions
- Causes:
- Increased HCO3 gain
- Loss of nonvolatile acid
- Decreased mineralocorticoid
- Respiratory compensation: increased alveolar ventilation, decreasing PaCO2
Hypoxia
- 4 main causes:
- Hypoxemic hypoxia: reduced PO2 of arterial blood
- Anemic hypoxia: reduced functioning hemoglobin available for oxygen transport
- Ischemic or hypoperfusion hypoxia: low blood flow prevents adequate O2 delivery
- Histotoxic hypoxia: toxic agents prevent cellular utilization of O2
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