3.3 Acid-Base Balance
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Questions and Answers

How do the respiratory and renal mechanisms help compensate for alkalosis and acidosis?

  • By restoring the body's acid-base balance (correct)
  • By increasing the intake of acidic foods
  • By reducing lung function
  • By affecting blood sugar levels

    • What is the role of buffer systems in the human body?

  • To increase respiratory rate
  • To maintain stable pH levels (correct)
  • To regulate blood sugar levels
  • To cause acidosis

    • In uncompensated respiratory acidosis, what is the main change in arterial blood gases?

  • PCO2 is constant
  • Plasma [HCO3-] changes (correct)
  • No compensation mechanisms exist
  • Plasma pH change is always greater

    • Of the following, what is the likely cause of a patient with pH 7.25, PaCO2 25, PaO2 62, HCO3- 15?

    <p>Diabetic ketoacidosis</p> Signup and view all the answers

    What is the most important acid-base buffer system in the blood?

    <p>Bicarbonate-Carbonic Acid System</p> Signup and view all the answers

    Which of the following is NOT a major acid in fixed acids removed by the kidneys?

    <p>Acetic acid</p> Signup and view all the answers

    How does the respiratory system control CO2 levels in the body?

    <p>By altering ventilation to change PaCO2</p> Signup and view all the answers

    Which buffer system is the major buffer of interstitial fluid?

    <p>Bicarbonate buffer system</p> Signup and view all the answers

    What type of rapid response occurs when there is an increase in arterial [H+] due to ketoacidosis?

    <p>Increase in ventilation rate</p> Signup and view all the answers

    How does the bone salts of hydroxyapatite contribute to acid-base balance?

    <p>By buffering H+ ions in chronic acidosis</p> Signup and view all the answers

    What is the role of the respiratory system in acid-base regulation?

    <p>Excreting most of the CO2 formed by metabolism</p> Signup and view all the answers

    How is pH related to the concentration of hydrogen ions in a solution?

    <p>pH increases as the concentration of hydrogen ions decreases</p> Signup and view all the answers

    Which system resists pH changes by removing volatile acids?

    <p>Respiratory system</p> Signup and view all the answers

    What is the pH of gastric acid in the body?

    <p>~ 1</p> Signup and view all the answers

    Which buffer system is weaker than the bicarbonate system?

    <p>Phosphate buffer system</p> Signup and view all the answers

    Which of the following DOES NOT cause respiratory alkalosis?

    <p>Decreased CO2 elimination</p> Signup and view all the answers

    Which condition results in metabolic acidosis?

    <p>Loss of bicarbonate ions</p> Signup and view all the answers

    What happens to blood pH during respiratory alkalosis?

    <p>It increases</p> Signup and view all the answers

    How does the respiratory system assist in regulating pH?

    <p>By regulating the concentration of H+ ions through PaCO2</p> Signup and view all the answers

    What causes metabolic acidosis?

    <p>Overproduction of H+ ions</p> Signup and view all the answers

    What is one cause of respiratory alkalosis?

    <p>Pulmonary embolism</p> Signup and view all the answers

    Metabolic alkalosis can be caused by excessive renal reabsorption of bases.

    <p>True</p> Signup and view all the answers

    Anion gap acidosis can result from an increased plasma concentration of anions other than chloride and bicarbonate.

    <p>True</p> Signup and view all the answers

    Metabolic alkalosis can result from the loss of hydrogen ions.

    <p>True</p> Signup and view all the answers

    Non-gap acidosis is commonly treated with sodium chloride (NaCl).

    <p>False</p> Signup and view all the answers

    Respiratory compensation in acidosis involves a decrease in minute ventilation.

    <p>False</p> Signup and view all the answers

    In the context of hypoxemia, what is the main cause of anemic hypoxia?

    <p>Inadequate number of erythrocytes</p> Signup and view all the answers

    Which condition involves toxic agents preventing cellular utilization of oxygen, as described in the text?

    <p>Histotoxic hypoxia</p> Signup and view all the answers

    What is the consequence of a left shift in P50 as mentioned in the text?

    <p>Increased risk of dysrhythmias</p> Signup and view all the answers

    How does acetazolamide contribute to acid-base balance, as outlined in the text?

    <p>Increases renal excretion of HCO3</p> Signup and view all the answers

    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:
      1. Lungs remove volatile acids (~20,000 mmol CO2/day)
      2. Kidneys remove fixed acids (~ 100 mEq/day)
      3. 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:
      1. Increased H+ secretion into the tubular fluid
      2. 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

    • 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++

    • Anion gap = Major cations - Major anions = 8-12 mEq/L

    • Anion gap >14 mEq/L = Anion gap acidosis

    • Anion gap < 14 mEq/L = Non-anion gap acidosis

    • Treat underlying cause### Acid-Base Balance

    • 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)

    • 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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