Questions
3 questions per exam
Difficulty
Medium-Hard
Importance
Core curriculum for medical and paramedical bioscience papers
Overview
Acid-Base and Electrolyte balance is a critical physiological regulatory system essential for maintaining homeostasis in the human body. Mastery of this topic is vital for understanding clinical biochemical pathways and interpreting diagnostic data, making it a high-yield area in both written examinations and oral vivas.
Arterial Blood Gas (ABG) Interpretation
ABG analysis provides a snapshot of the body's acid-base status and gas exchange efficiency. Students must focus on the relationship between pH, partial pressure of CO2 (pCO2), and bicarbonate (HCO3-) to identify respiratory or metabolic disturbances.
- Normal pH: 7.35–7.45
- Normal pCO2: 35–45 mmHg
- Normal HCO3-: 22–26 mEq/L
- Henderson-Hasselbalch equation: pH = pKa + log([HCO3-]/[H2CO3])
- Respiratory Acidosis: low pH, high pCO2
- Metabolic Alkalosis: high pH, high HCO3-
Water and Electrolyte Balance
Electrolyte balance involves the precise regulation of ions like sodium, potassium, and chloride across fluid compartments. Disruptions in this balance can lead to severe clinical manifestations like cardiac arrhythmias or neurological impairment.
- Intracellular major cation: Potassium (K+)
- Extracellular major cation: Sodium (Na+)
- Osmolality calculation: 2(Na+) + Glucose/18 + BUN/2.8
- Role of Aldosterone in sodium retention
- Role of ADH in water reabsorption
Mineral Metabolism
This subtopic explores the regulation of calcium, phosphate, and magnesium levels through hormonal feedback loops. Understanding the antagonistic actions of PTH and Calcitonin is crucial for exam success.
- PTH increases serum calcium levels
- Calcitonin decreases serum calcium levels
- Vitamin D facilitates intestinal calcium absorption
- Hypocalcemia leads to tetany
- Inverse relationship between serum Calcium and Phosphate
Formula Sheet
pH = pKa + log([HCO3-]/0.03 * pCO2)
Anion Gap = [Na+] - ([Cl-] + [HCO3-])
Osmolality = 2[Na+] + [Glucose]/18 + [BUN]/2.8
Exam Tip
Always identify the primary pH abnormality first, then determine if the pCO2 or HCO3- matches the pH to distinguish between respiratory or metabolic origins before checking for compensation.
Common Mistakes
- Confusing compensatory mechanisms for primary disturbances in ABG analysis.
- Misinterpreting the inverse relationship between serum calcium and phosphorus in metabolic conditions.
- Neglecting the significance of the anion gap in determining the cause of metabolic acidosis.
More Revision Notes
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