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Questions and Answers
What is the primary function of buffers in acid-base physiology?
Which buffer system provides the largest proportion of buffer capacity in the body?
Which of the following is NOT a type of acid produced in the body?
How does renal compensation primarily affect the extracellular fluid?
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What role do ammonia (NH3) and ammonium (NH4+) ions play in the body?
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What component of a buffer system is present in greater concentration at low pH levels?
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Which buffer system is primarily responsible for maintaining pH in the extracellular fluid?
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Under what condition can the weak acid (HA) contribute H+ ions in a buffer system?
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What is the primary role of hemoglobin in blood buffering?
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Why is the phosphate buffer system considered unimportant in blood?
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What occurs to [H+] when pH increases from 7.4 to 7.6?
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What is the effect on [H+] when pH decreases from 7.4 to 7.2?
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Which statement about changes in pH is correct?
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Which of the following pH values corresponds to extreme acidosis?
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What is a characteristic of volatile acids in the body?
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Which acid is considered a non-volatile acid produced from protein catabolism?
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What pH level indicates maximum urine acidity?
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Which of the following is associated with diabetic ketosis?
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What is the primary role of the kidneys in acid-base balance?
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How do buffers respond to acid-base disturbances?
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Which factor is the primary regulator of ventilation and acid-base balance?
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What happens to bicarbonate when plasma levels exceed 26 mEq/L?
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What does decreased bicarbonate or increased PCO2 indicate?
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How do both PCO2 and bicarbonate levels contribute to pH maintenance?
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What is the effect of hyperventilation on acid-base balance?
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What occurs to filtered bicarbonate when plasma bicarbonate is low?
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What is a common cause of metabolic alkalosis?
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What happens to pH during respiratory alkalosis?
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Which statement about renal compensation in respiratory alkalosis is accurate?
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What primary condition leads to respiratory acidosis?
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Which of the following is involved in metabolic alkalosis correction?
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What physiological change mainly characterizes respiratory compensation for metabolic alkalosis?
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In respiratory alkalosis caused by hyperventilation, what happens to HCO3- levels?
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What is a common feature of metabolic alkalosis?
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Study Notes
Acid-Base Balance
- Acid-base physiology is the study of H+ concentration ([H+]) regulation in the extracellular fluid (ECF).
- [H+] is tightly regulated through powerful homeostatic mechanisms: buffers, respiratory compensation, and renal compensation.
- The bicarbonate buffer system is considered the most important buffer due to its high concentration and the tight regulation of both CO2 and HCO3- by the lungs and kidneys.
- Buffer effectiveness depends on its concentration and pK (dissociation constant).
- Buffers are weak acids and their conjugate bases. At low pH, weak acid [HA] dominates, and at high pH, conjugate base [A-] dominates.
- Buffers prevent drastic pH changes by absorbing or releasing H+ ions as needed.
Buffer Systems in the Body
- The major buffers in the body include:
- Bicarbonate: Primary buffer in the ECF, comprising 53% of total buffering. It has a low pK (6.1) but its high concentration and the regulation of both H2CO3/CO2 and HCO3- make it very effective.
- Hemoglobin: Second most important buffer, accounting for 35% of total ECF buffering. Imidazole groups on histidine and α-amino groups act as primary buffer sites on proteins.
- Proteins: Contribute 7% of total ECF buffering. They have good pK values (6.4-7.9) but their concentrations are too low.
- Phosphate: Less significant in blood due to low concentration, it's more important in urine where its concentration is higher.
Measuring Acid-Base Status: pH & H+ concentration
- pH is a logarithmic measure of H+ concentration. A change of 0.2 pH units represents a significant change in [H+].
- Normal pH in plasma is 7.4, corresponding to an [H+] of 0.00004 mEq/L.
- Acidosis: pH below 7.35, reflecting increased [H+].
- Alkalosis: pH above 7.45, reflecting decreased [H+].
- Different body fluids have varying pH and H+ concentrations.
Sources of H+ in the Body
- Volatile acid: Primarily CO2, produced by aerobic metabolism of cells and eliminated by the lungs.
- Non-volatile or fixed acids: Examples include sulfuric acid from protein catabolism, phosphoric acid from phospholipid catabolism, and lactic acid from exercise.
- Other acid loads: Result from diabetic ketoacidosis, poisoning ingestion, etc.
Acid-Base Disorders
- Metabolic acidosis: Decreased [HCO3-] or increased non-volatile acid load, resulting in decreased pH (less than 7.35).
- Metabolic alkalosis: Increased [HCO3-] or loss of H+, leading to increased pH (greater than 7.45).
- Respiratory acidosis Increased PCO2 (CO2 retention), resulting in decreased pH (less than 7.35).
- Respiratory alkalosis: Decreased PCO2 (CO2 loss), leading to increased pH (greater than 7.45).
Compensation Mechanisms
- Buffers: Rapidly minimize pH changes but cannot restore pH to normal.
- Respiratory compensation: Lungs regulate CO2 levels by altering ventilation rate.
- Renal compensation: Kidneys regulate HCO3- levels through reabsorption, secretion, and new synthesis.
Respiratory Control of CO2
- Lungs primarily regulate ventilation rate based on PCO2 levels.
- Hyperventilation lowers PaCO2, resulting in alkalosis.
- Hypoventilation raises PaCO2, resulting in acidosis.
Renal Control of Bicarbonate
- Kidneys maintain plasma [HCO3-] within a narrow range (22-26 mEq/L).
- HCO3- recovery: Kidneys recover filtered HCO3- when plasma [HCO3-] is below 26 mEq/L.
- HCO3- synthesis: Kidneys synthesize “new” HCO3- when plasma [HCO3-] is above 26 mEq/L.
- HCO3- excretion: Kidneys excrete excess HCO3- in urine.
Mechanisms of Renal Bicarbonate Recovery
- The process is driven by H+ secretion.
- H+ is formed in the intracellular fluid by the reaction of CO2 and water catalyzed by carbonic anhydrase.
- H+ is exchanged for Na+ (primarily in the proximal tubule) or actively secreted (in the distal tubule).
- HCO3- enters the peritubular capillary blood.
Titratable Acidity & Ammonia (NH3) & Ammonium (NH4+) Ions
- Titratable acidity: Refers to the acid excreted in the urine that can be titrated with a base.
- Ammonia (NH3) and ammonium (NH4+) ions: NH3 is produced by renal cells and combines with H+ to form NH4+, which is excreted in the urine. This process is critical for generating new HCO3- and removing excess acid from the body.
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Description
Test your understanding of acid-base physiology and the mechanisms that regulate hydrogen ion concentration in the body. This quiz covers buffer systems, especially the bicarbonate buffer system, and their importance in maintaining pH balance. Challenge yourself with questions on homeostatic mechanisms, buffer effectiveness, and the major buffers in the body.
