Renal Physio/Diuretics Flashcards
What are the constituents of the body fluid compartments?
- TBW = 60% of weight
- ICF = 40%
- ECF = 20% (Plasma 25%, Insterstitial fluid 75%)
What is the major determinant of ECF osmolarity?
- sodium!
- this in turn determines ECF volume and is under tight neurohormonal control
How is edema maintained physiologically?
- decreased circulating volume due to a shift in fluid distribution from the intravascular to extravascular space
- leads to decreased renal perfusion pressure, which activates the renin-angiotensin-aldosterone system
- this increases sodium retention and maintains edema
Describe the reabsorption of solutes and water in the proximal tubule
- leaky epithelium which is unable to maintain an osmotic gradient, so reabsorption of solutes and water occurs isosmotically
- 67% Na reabsorbed
- 67% K reabsorbed
Describe the movement of solutes and water in the loop of Henle
- thin descending limb is in the medulla and is permeable to water, but not solutes
- thick ascending limb is in medulla and cortex and maintains counter current multiplication (permeable to solutes but not water)
- 25% Na reabsorbed in thick ascending limb
- 20% K reabsorbed in thick ascending limb
Describe the movement of solutes and water in the distal tubule
- early distal tubule is impermeable to water, which dilutes the tubular fluid
- late distal tubule is permeable to water when induced by ADH
- sodium reabsorption in late distal tubule is determined by aldosterone
- 5% Na reabsorbed
- variable absorption and secretion of K
Describe the movement of solutes and water in the collecting duct
- water reabsorption is induced by ADH
Give me the clearance equation, and throw in the fraction excretion equation while you’re at it
Cl = (V x [U])/[P]
FE = clearance of solute / GFR
What is the FE of water and sodium when A) in balance, B) in negative water balance, and C) in positive water balance?
A) 1%
B) FEwater <1% (dehydration), FE(Na) = 1
C) FEwater = 1-5+%, minimal effect on FE(Na)
What is the maximum FE(Na) for each segment of the nephron?
1) proximal tubule = 5% (CAIs)
2) thick ascending limb = 25% (Loops)
3) early distal tubule = 8% (thiazides)
4) late distal tubule/collecting duct = 2% (potassium sparing)
How do carbonic anhydrase inhibitors work? Name 3; what are these used for and what are the side effects?
- MOA; inhibit CA in the lumen of the proximal tubule, which blocks the dehydration of H2CO3 and decreases Na reabsorption
- acetazolamide, methazolamide, dichlorphenamide
- used for glaucoma, mountain sickness
- SE: hypokalemia, metabolic acidosis, possible ammonia toxicity and hepatic encephalopathy
A patient presents with elevated ICP. What do you administer to reduce this, how does it work, and what side effects should you be watching for?
- mannitol, an osmotic diuretic
- MOA: non reabsorbable solute which has an osmotic pressure that opposes the isotonic absorption of water
- SE: increase in ECF volume, pulmonary edema
What are the therapeutic uses of mannitol?
- treatment of drug OD to hasten the clearance
- in shock to mimimize risk of acute renal failure
- reduce intraocular or intracranial pressure
- diagnose oliguria
You’re looking at a urinary sample analysis and see increased Na, increased K, increased Ca, increased Mg, and increased Ca. When checking blood work, you notice the same patient is alkalotic. What kind of diuretic are they on?
- loop diuretic (furosemide, torsemide, ethacrynic acid, bumetanide)
How do the loop diuretics work, and what are they used for?
- inhibits Na/K/2Cl pump in the thick ascending limb
- used when you need quick diuresis (crisis edema)
- increases venous compliance (prostaglandins)
- treatment of hypercalcemia
- can work with low GFR (<30-40)
- SE: hypokalemia, ototoxity
