Lecture 21: Renal Interventions Flashcards
Flashcard: Q: How do the cardiovascular and renal systems interact to regulate fluid balance?
A:
The kidneys receive about 20% of cardiac output, which they filter to maintain fluid and electrolyte balance.
When cardiac output decreases (e.g., in heart failure), renal perfusion drops, triggering RAAS activation.
- Renin converts angiotensinogen to ANG I, which is converted to ANG II.
- ANG II causes vasoconstriction and stimulates aldosterone release, increasing Na⁺ and water retention.
This compensation helps maintain blood pressure but can lead to fluid overload and oedema in conditions like heart failure.
Flashcard: Q: What are the main classes of diuretics, and give an example of each?
A:
1. Loop Diuretics (e.g., Furosemide): Inhibit Na⁺-K⁺-2Cl⁻ cotransporter in the ascending loop of Henle.
2. Thiazide Diuretics (e.g., Hydrochlorothiazide): Inhibit Na⁺/Cl⁻ cotransporter in the distal convoluted tubule.
3. Potassium-Sparing Diuretics:
- ENaC Inhibitors (e.g., Amiloride)
- Aldosterone Receptor Antagonists (ARAs) (e.g., Spironolactone).
3. Carbonic Anhydrase Inhibitors (e.g., Acetazolamide): Reduce bicarbonate reabsorption in the proximal tubule.
4. Osmotic Diuretics (e.g., Mannitol): Increase tubular osmolarity, pulling water into the urine.
5. Miscellaneous (e.g., SGLT2 Inhibitors): Inhibit sodium-glucose transport.
Flashcard: Q: What are the mechanisms of action of the different diuretics? loop
A:
1. Loop Diuretics: Inhibit the Na⁺-K⁺-2Cl⁻ transporter in the ascending loop of Henle, reducing Na⁺ reabsorption and increasing urine output.
Flashcard: Q: What are the mechanisms of action of the different diuretics? thiazide
A:
2. Thiazide Diuretics: Block the Na⁺/Cl⁻ cotransporter in the distal convoluted tubule, reducing Na⁺ reabsorption.
Flashcard: Q: What are the mechanisms of action of the different diuretics? potassium sparing
- Potassium-Sparing Diuretics:
- ENaC Inhibitors: Block Na⁺ channels in the collecting duct, preventing Na⁺ reabsorption.
- ARAs: Inhibit aldosterone from promoting Na⁺ reabsorption and K⁺ excretion.
Flashcard: Q: What are the mechanisms of action of the different diuretics? carbonic anhydrase
- Carbonic Anhydrase Inhibitors: Inhibit carbonic anhydrase, reducing HCO₃⁻ reabsorption and promoting diuresis.
Flashcard: Q: What are the mechanisms of action of the different diuretics? osmotic
- Osmotic Diuretics: Increase osmolarity of tubular fluid, pulling water into the urine by osmosis.
Flashcard: Q: How do diuretics affect fluid balance in the body?
A:
Diuretics increase urine output by inhibiting sodium and water reabsorption at different sites in the nephron.
Loop diuretics are the most potent, leading to significant fluid loss and reduction of blood volume.
Thiazides are used primarily for hypertension, as they cause moderate fluid loss.
Potassium-sparing diuretics preserve potassium while promoting modest sodium excretion.
Prolonged use of diuretics can lead to electrolyte imbalances like hypokalaemia (except in potassium-sparing diuretics) and dehydration, which affects overall fluid homeostasis.
Flashcard: Q: Why are diuretics sometimes used as a form of doping in sports?
A:
Diuretics cause rapid fluid loss, which can be used for rapid weight reduction (e.g., in weight-class sports like boxing).
They are also used to mask other banned substances in urine by diluting urine samples, making it harder to detect certain drugs.
Diuretics were first banned by the World Anti-Doping Agency (WADA) in 1988 due to their abuse for these purposes.
Q: How do most diuretics exert their effect in the nephron?
A: Most diuretics act by targeting ion transport receptors on the luminal surface of the nephron tubules, inhibiting ion reabsorption. ARAs act on cytosolic receptors.
Q: How are diuretics transported into the nephron if they are bound to albumin in the blood?
A: Diuretics bound to albumin must be actively secreted into the nephron via OATs (Organic Anion Transporters) or OCTs (Organic Cation Transporters) in the proximal tubule.
Q: How do loop diuretics work?
A: Loop diuretics inhibit the NKCC2 cotransporter in the thick ascending limb of the loop of Henle, blocking reabsorption of Na⁺, K⁺, and Cl⁻, which increases sodium delivery to the distal tubule and causes significant diuresis.
Q: What are the side effects of loop diuretics?
A: Increased sodium delivery to the distal tubule triggers potassium (K⁺) and hydrogen ion (H⁺) excretion, leading to hypokalaemia and metabolic alkalosis.
