Renal Physiology, Body Fluid Compartments, Electrolytes and Acid-Base Homeostasis — WACS Viva & Clinical Scenarios (Physiology and Applied Physiology)

Exam-style renal physiology, body fluid compartments, electrolytes and acid-base homeostasis viva scenarios with examiner probes and model answers for…

Scenarios covered

• SCENARIO 1: Describe the Countercurrent Multiplier mechanism in the loop of Henle and the Countercurrent Exchange system in the vasa recta. Explain how a hyperosmolar medullary interstitial gradient is established and maintained, and describe the cellular mechanisms of action of antidiuretic hormone (vasopressin) on the collecting duct.
• SCENARIO 2: A 55-year-old male with long-standing bowel obstruction presents with severe dehydration and metabolic alkalosis. Outline the body fluid compartments in a 70 kg adult male, giving volumes and normal ionic compositions of the intracellular and extracellular compartments. Detail the indicator dilution principle and the specific tracers used to measure each compartment.
• SCENARIO 3: Define Glomerular Filtration Rate (GFR) and Filtration Fraction. State the Starling equation for glomerular ultrafiltration, explaining each variable. Describe the myogenic and tubuloglomerular feedback mechanisms responsible for renal blood flow and GFR autoregulation between mean arterial pressures of 75 and 160 mmHg.
• SCENARIO 4: Write comprehensive physiological notes on potassium homeostasis. Differentiate between internal potassium balance (transcellular shifts) and external potassium balance (renal excretion), detailing the hormonal, acid-base, and pharmacological factors that modulate each system.
• SCENARIO 5: Explain the physiology of acid-base balance using both the classical Henderson-Hasselbalch approach and the Stewart physicochemical approach. Define Strong Ion Difference (SID), Total Weak Non-Volatile Acids (Atot), and the Anion Gap, explaining the biochemical basis of normal anion gap hyperchloraemic metabolic acidosis resulting from large-volume 0.9% saline infusion.