Diuretics, Hemodialysis, and Erythropoietin Flashcards
A ___ is a drug that increases urine output due to their actions on the kidney. They are often called “water pills” (all inhibit water reabsorption), but they can increase excretion of things as well.
diuretic
What reasons would one prescribe a diuretic in a patient with CHF or HTN?
CHF: heart weakens → ↓ cardiac output → ↓ GFR → ↑ aldosterone → ↑ Na+ and H2O reabsorption → ↑ ECV and edema
HTN: ↑ ECV → ↑ plasma volume → ↑ blood pressure
Match:
- osmotic diuretics
- CA inhibitors
- Loop diuretics
- Thiazides
- K+ sparing
- Aquaretics
A. reduce Na+ reabsorption at the proximal tubule (major site)
B. block Na+/Cl- symporter in early distal tubule
C. retain water by increasing osmotic pressure; act in water-permeable segments of the nephron (PT and descending loop of Henle)
D. ADH receptor antagonists
E. act in late distal tubule and cortical collecting duct to inhibit sodium reabsorption AND potassium secretion
F. act in thick ascending limb to inhibit Na+ reabsorption via the Na+/K+/2Cl- symporter
1 - C 2 - A 3 - F 4 - B 5 - E 6 - D
What are the two classes of K+ sparing diuretics?
- aldosterone
2. ENaC blockers
___ diuretics increase the osmotic pressure in the tubular fluid and thus impair Na+ reabsorption. What are some examples.
Osmotic
mannitol and pathologically elevated glucose
How do osmotic diurectics work?
- gain access to tubule by glomerular filtration due to small size
- are poorly reabsorbed (mannitol - no transporter; glucose - saturates transporter so not all reabsorbed)
- will have an effect where tubule is freely permeable to water
- some of what’s not reabsorbed in PT and DL can be reabsorbed downstream, but typically results in excretion of 10% of filtered Na+
note: ↓ water reabsorption → ↓ Ca2+ reabsorption by solvent drag (there is no osmotic gradient established by Na+ so Ca2+ not reabsorbed
___ ___ inhibitors reduce Na+ reabsorption by inhibiting CA, thus reducing the H+ available for the Na+/H+ antiporter. Give an example.
Carbonic anhydrase
Acetazolamide
CA inhibitors gain access to the proximal tubule via ___.
secretion
most of the effect is in the PT where ~1/3 of Na+ reabsoprtion relies on the Na+/H+ antiporter
Why is the effect of CA inhibitors not large?
- the downstream segments will increase Na+ reabsorption when tubular Na+ increases
- typically increases Na+ excretion to 5-10% of filtered load
___ diuretics are the most powerful of all diuretic. How do thy work? Give an example.
Loop
they inhibit Na+ reabsorption in the ascending limb of the loop of Henle
Furosemide (lasix)
T/F. Loop diuretics are filtered not secreted into the proximal tubule.
False, they are secreted NOT filtered
Loops inhibit the ___ symporter in the ___ ___ limb which inhibits Na+ reabsorption. What happens as a result?
Na+/K+/2Cl-; thick ascending
- urine leaving the loop is not dilute
- no osmotic gradient established in the medulla interstitium so water not reabsorbed along collecting duct → urine is dilute (500 mOsm instead of 1400 mOsm)
- can increase Na+ excretion to as much as 25% of filtered load, because Na+ reabsorption capacities downstreams of their site of action are limited
Thiazide diuretics, like ___, are ___ into the PT, but where do they act?
chlorothiazide; secreted
they act in the distal tubule to block the Na+/Cl- transporter
T/F. With thiazides, the kidney’s ability to dilute urine is diminished.
True.
With thiazides, reabsorption of water still occurs in the collecting duct, but ___-___% of the filtered Na+ is excreted.
5-20
K+-sparing diuretics act where K+ is normally ___ into the tubular fluid by the ___ cells.
secreted; principal
How does spironolactone work?
Aldosterone antagonists block aldosterone’s ability to increase Na+ transporters in principal cells
How does amiloride work?
ENaC blockers block Na+ reabsorption across the apical membrane. These act on a membrane protein so can gain access by secretion into the PT.
T/F. Continued use of diuretics become more effective.
False, continued use of diuretics become LESS effective because volume contraction counteracts the effects of the diuretic.
Diuretics decrease ECV so compensatory mechanisms are activated in response to the nervous and endocrine system. Explain this process.
- ↑ sympathetic activity in response to reduced BP → ↓ GFR → ↑ PT reabsorption and ↑ renin
- ↓ natriuretic peptides
- secrete renin from JGA → ↑ angiotensin II and aldosterone ↓ Na+ excretion
- stimulate ADH release → ↓ water excretion
___ removes waste products from the blood when kidney function has been impaired.
Hemodialysis
In a kidney-failure patient undergoing dialysis, the blood is briefly removed from the body to be circulated through a ___, which is a cylindrical bundle of hollow fibers. The walls of the fibers are made of a semipermeable membrane with ___ of defined size that allow small molecules to diffuse into the dialysis fluid. The fluid and blood move in ___ directions to remove nitrogenous and other wastes, and adjust osmolarity before the blood is returned to the body.
dialyzer; pores; countercurrent
The concentration of ___ in the dialysis fluid is similar to that in plasma. ___, ___, and ___ diffuse from blood into dialysis fluid. ___ is high in the dialysis fluid so it diffuses into blood to correct blood ___.
Na+; Urea; potassium; phosphate; Bicarbonate; acidity
Match the following:
- catheter
- AV fistula
- AV graft
A. preferred for long term treatment; creates an anastomosis between artery and vein. Arterial blood is withdrawn, and blood is returned to the vein after dialysis.
B. used to access venous blood for short-term treatment; scarring, vessel narrowing or occlusion can occur
C. uses an artificial/synthetic vessel to join an artery and vein when vascular problems do not permit using a fistula; can become narrowed which can lead to clotting and/or infections.
1 - B
2- A
3 - C
