MRCEM PART 1|Physiology Part 3

Renal Physiology Part 3: Calcium, Diuretics, & GFR Basics
Welcome to Physiology Part 3 of our MRCEM revision series! Today, we finalize our look at electrolyte handling and start discussing glomerular function, covering high-yield topics essential for your exam.

1. Calcium Reabsorption

Freely Filtered: Calcium passes easily into the nephron.

Regulated in DCT: Fine-tuning occurs in the Distal Convoluted Tubule (DCT).

Hormonal Control: Parathormone (PTH) and Activated Vitamin D (D3) control the Calcium ATPase channel on the basolateral membrane (into the blood). The Sodium-Calcium Antiporter works independently.

2. Diuretics: Mechanism and Side Effects

Osmotic Diuretics (e.g., Mannitol): Not reabsorbed, stay in the tubule, draw water out, causing polyuria (e.g., in uncontrolled diabetes).

Loop Diuretics (Most Potent): Inhibit the Sodium-Potassium-2-Chloride Symporter in the Loop of Henle. Major side effect: Hypokalemia.

Thiazide Diuretics: Inhibit the Sodium-Chloride Co-transporter in the early DCT. Indirectly cause Hypokalemia via aldosterone activation.

Potassium-Sparing Diuretics (e.g., Spironolactone, Amiloride): Aldosterone inhibitors that prevent Potassium excretion, counteracting hypokalemia.

3. Glomerular Filtration Rate (GFR)

Filtration Fraction: The percentage of plasma filtered by the kidney. FF=GFR/RPF=120/600=20%.

Protein Concentration: Proteins are not filtered, becoming more concentrated in the Efferent Arteriole.

Starling Forces: Filtration is driven by Hydrostatic Pressure (35 mmHg) and opposed by Oncotic Pressure (25 mmHg).

Net Filtration Pressure (NFP): 10 mmHg (Hydrostatic is greater, so filtration occurs).

Join us in the next video as we complete the discussion on the Filtration Barrier! Hit like and subscribe!
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