158. Principles of Acid-Base Homeostasis – Quiz

📌 Professor’s Notes: Quick Revision

High-yield revision notes for rapid review before university examinations.

• Normal arterial blood pH is 7.35–7.45. Acid–base balance depends on continuous acid production, buffering and elimination. Buffers act immediately, the lungs regulate carbon dioxide, and the kidneys regulate hydrogen ions and bicarbonate.
• pH is the negative logarithm of hydrogen ion concentration. A lower pH means greater acidity. A buffer contains a weak acid and its conjugate base and resists changes in pH. pK is the pH at which the concentrations of the weak acid and conjugate base are equal.
• Important acids produced in the body include carbonic, sulfuric, phosphoric, lactic and ketoacids. Carbon dioxide forms the major volatile acid and is eliminated by the lungs. Nonvolatile acids cannot be removed by the lungs and are mainly excreted by the kidneys.
• Major buffer systems are bicarbonate, plasma proteins, phosphate and hemoglobin. The bicarbonate–carbonic acid system is the principal extracellular buffer. Its normal bicarbonate-to-carbonic acid ratio is approximately 20:1, maintaining a blood pH near 7.40.
• Hemoglobin is the major nonbicarbonate buffer inside red blood cells. Deoxygenated hemoglobin binds hydrogen ions more readily than oxygenated hemoglobin, helping transport carbon dioxide without major changes in intracellular pH.
• Respiratory regulation acts within minutes. Increased hydrogen ions or carbon dioxide stimulate chemoreceptors, increasing the rate and depth of breathing. Hyperventilation lowers carbon dioxide and raises pH, whereas hypoventilation has the opposite effect.
• The kidneys provide the major long-term regulation. They secrete hydrogen ions, reabsorb filtered bicarbonate and generate new bicarbonate. Nearly all filtered bicarbonate is normally reabsorbed, with about 80–85% occurring in the proximal tubule.
• Renal hydrogen ion excretion occurs mainly through ammonium and titratable acids. Ammonium production from glutamine increases markedly during chronic metabolic acidosis and is an important mechanism for eliminating acid and generating new bicarbonate.
• The four major acid–base disorders are metabolic acidosis, respiratory acidosis, metabolic alkalosis and respiratory alkalosis. Compensation reduces the severity of the disorder but does not completely correct the primary abnormality.
• Metabolic acidosis is primarily a fall in plasma bicarbonate. Causes include diabetic ketoacidosis, lactic acidosis, renal failure and severe diarrhea. Respiratory compensation is hyperventilation with reduced carbon dioxide, while renal compensation increases hydrogen ion and ammonium excretion and bicarbonate regeneration.
• Respiratory acidosis results from inadequate alveolar ventilation and carbon dioxide retention. Renal compensation increases hydrogen ion secretion, ammonium and titratable acid excretion, and bicarbonate regeneration.
• Metabolic alkalosis is characterized by increased plasma bicarbonate. Vomiting, gastric suction, diuretic use and mineralocorticoid excess are important causes. Severe alkalemia can reduce ionized calcium and cause cramps, carpopedal spasm or tetany.
• Respiratory alkalosis results from excessive alveolar ventilation and reduced carbon dioxide. Its causes include high altitude, fever, sepsis, anxiety, pulmonary disorders and excessive mechanical ventilation. Renal compensation decreases bicarbonate reabsorption and increases bicarbonate excretion.