Renal Physiology Module 13.5 Questions Spring 2010

Front 1

How do most diuretics work?

Back 1

They decrease the rate of reabsorption of fluid from the tubules.

Front 2

What is a diuretic?

Back 2

A substance that increases the rate of urine output, and this reduces the total amount of fluid in the body.

Front 3

All useful diuretics cause ____ (sodium loss) as well as diuresis.

Back 3

Natriuresis.

Front 4

How does water act as a diuretic?

Back 4

Inhibits vasopressin secretion.

Front 5

How does ethanol act as a diuretic?

Back 5

Inhibits vasopressin secretion

Front 6

How do V2-vasopressin receptor agonists act as diuretics?

Back 6

Inhibit the action of vasopressin on the collecting ducts.

Front 7

How do large quantities of osmotically active substances such as mannitol and glucose act as diuretics?

Back 7

Produce osmotic diuresis.

Front 8

How do Xanthines such as caffeine and theophyline act as diuretics?

Back 8

Decrease tubular reabsorption of sodium and increase GFR.

Front 9

How do Carbonic Anhydrase inhibitors such as acetazolamide/Diamox work as diuretics?

Back 9

Decrease H+ secretion and increase Na+ and K+ excretion (Water follows solute)

Front 10

How does Metolazone (Zaroxolyn) and thiazides such as chlorothiazise/Diuril act as diuretics?

Back 10

Inhibit Na+Cl- cotransporter in the early portion of the distal tubule.

Front 11

How do loop diuretics such as furosemide/Lasix and ethacrynic acid (Edecrin) and bumetanide work as diuretics?

Back 11

Inhibit Na+K+2Cl- cotransporter in the medullary thick ascending limb of the loop of Henle.

Front 12

How do K+ retaining natriuretics such as spironolactone(Aldactone), triamterene(Dyrenium) and amiloride(Colectril) work as diurietics?

Back 12

Inhibit Na+K+ exchange in the collecting ducts by inhibiting the action of aldosterone or by inhibiting ENaC

Front 13

What are some common sites of actions of diuretics on the neprhon?

Back 13

Proximal Tubule.
Thick Ascending limb.
Distal tubule.
Cortical Collecting Ducts.
Inner Medullary collecting duct.

Front 14

What are some things that the overall effect of a particular diuretic depends on?

Back 14

The nephron segment where the diuretic acts.

The response of the nephron segments distal to the site of action of the diuretic.

The delivery of sufficient quantities of the diuretic to its site of action.

The volume of the ECF compartment.

Front 15

How are diuretics "self-limiting"?

Back 15

Diuretic causes natriuresis and decreases ECF which then decreases GFR and increases PT reabsoprtion in response, limiting the natriuretic response.

Front 16

How do osmotic diuretics work?

Back 16

(Urea, Mannitol, Glucose).

Water is lost in the urine instead of being reabsorbed because of the osmotically active substances in the tubules.

However, Sodium that is not reabsorbed by the PT is reabsorbed downstream by the TALH which can significantly increase its reabsorption when a large load is delivered, thus limiting how useful osmotic diuretics are.

Front 17

What is one drawback to using a carbonic anhydrase inhibitor as a diuretic?

Back 17

The TALH can just increase Na+ reabsorption when its load is increased.

And I'm also assuming there would be some acid-base disruptions happening too.

Front 18

What is a common complication of using a Loop diuretic such as Furosemide?

Back 18

K+ is also excreted and depleted!

However, this is one of the most powerful diuretics due to its action on a distal part of the nephron where Na+ reabsorption beyond it is limited.

Front 19

True or False:

All diuretics increase K+ excretion.

Back 19

False..

But true in a sense too (Sorry guys).

All of them DO increase K+ excretion, except for K+ "sparing" diuretics. (No examples given?)

Front 20

How do diuretics cause K+ excretion?

Back 20

Increases tubular flow rate resulting from inhibition of Na+ reabsorption upstream from the distal tubules and CD results in additional amounts of Na+ to the region of K+ secretion, thus stimulating an increase in K+ secretion.

Also an increase in ADS secretion will lead to an increase in K+ secretion due to the changes in Na+ balance.

Front 21

Carbonic anhydrase inhibitors can cause metabolic ____ whereas loop diuretics can cause metabolic ____.

Back 21

CAI: Metabolic acidosis.

Loop diuretics: Metabolic alkalosis.

Front 22

While Potassium sparing diuretics may prevent excess excretion of potassium, what problem can it have?

Back 22

Causing metabolic acidosis. (Due to inhibiting H+ secretion)

Front 23

What are some other substances that can have their reabsorption/secretion affected by diuretics?

Back 23

Calcium. (Excretion is increased)

PO4: (Excretion is increased, however will be reduced with long-term diuretic usage.)

Front 24

What are two commonly used screening tests for evaluating glomerular function?

Back 24

BUN (Blood Urea Nitrogen) and Cr (Serum creatinine)

Front 25

True or False:

BUN will rise in proportion to the reduction in GFR.

Back 25

False.

Unfortunately it does not, and isn't the best indicator of GFR.

Front 26

Which is more affected by renal factors and which is better for determining GFR? Creatinine or BUN?

Back 26

BUN is more affected by renal factors.

Creatinine is less affected, and therefore a better indicator of GFR.

Front 27

Does the kidney tubule secrete creatinine ever?

Back 27

Yes, in some species.

(I think in the dog it does NOT ever secrete creatinine).

Front 28

What does an increase in BUN or Cr indicate?

Back 28

That 75% or more of the nephrons are not functioning.

Front 29

What are some possible interpretations of the finding of a reduced GFR?

Back 29

Pre-renal disease (IE dehydration)

Renal disease with a reduced glomerular filtration.

Post-renal disease with obstruction of urine flow in the lower urinary tract.

Front 30

What is USG? What is the normal range?

Back 30

USG= Urine Specific Gravity.

Normal range: 1.001-1.080

Front 31

What are three names for USG in relation to glomerular filtrate? (Urine Specific Gravity)

Back 31

Isosthernuria (1.007-1.015). Same concentration as unaltered glomerular filtrate.

Hyposthenuria (less than 1.007). Urine has a lower solute concentration than glomerular filtrate.

Hypersthenuria (greater than 1.015) Urine has a higher total solute concentration than glomerular filtrate.

Front 32

True or False:

Repeated findings of HIGH specific gravity is normal.

Back 32

True!

(It's when you constantly find LOW specific gravity that you should be thinking loss of kidney function (and ability of the urine to concentrate)).

Front 33

How much of nephron function can be lost before clincal tests reveal loss of renal function?

Back 33

Up to 2/3.

Front 34

Repeated specific gravities that are isosthernuric indicate what?

Back 34

Renal disease.

Front 35

What is a water deprivation test? What does it do?

Back 35

Tests tubular function (IE if the urine can be concentrated)

Indicated with PU/PD of undetermined cause in which there is a normal BUN and Cr.

The test is over when the patient either adequately concentrates urine or is dehydrated greater than 5% of body weight.

Front 36

in a normal animal, what is the fractional clearance of electrolytes usually?

Back 36

Less than 1.0 (Meaning there is conservation of electrolytes.)

Sodium has a value of 0-0.7%

Front 37

In animals with azotemia due to primary renal disease, what will happen to the fractional clearance of sodium?

Back 37

It will be higher than normal. (IE more in the urine)

Front 38

As more nephrons are lost, how does the kidney handle increases in Na+ intake?

Back 38

It's ability to respond is impaired, so the patient then experiences a positive Na+ balance with an increase in ECV (IE you see generalized and pulmonary edema)

Front 39

While an increased Na+ intake in animals with kidney failure can have serious problems, can a sudden decrease in Na+ intake also cause problems?

Back 39

Yes, the kidneys are impaired and so cannot adapt to sudden changes in Na+ intake.

Front 40

When renal failure is progressing, can functional nephrons take over for non-functional ones?

Back 40

Yes, that is why most of the kidney is usually lost before a clinical sign is seen, due to compensation by the healthy nephrons.

Front 41

What happens in glomerulonephritis?

Back 41

The glomeruli have become more permeable than normal so large amounts of protein are lost in the urine.

This is usually a result of immune-mediated damage to the kidneys.

Front 42

Case: You have a 3Yr SF springer spaniel (Uh-oh CD3 deficiency? Wait, that's in Brittneys...) that hasn't been eating well and tires easily. You notice edema in the limbs, and increased protein and RBC in the urine, as well as a low serum albumin. What's wrong with the dog?

Back 42

The dog has acute glomerulonephritis!

Proteinuria is indicative of glomerular disease. (Healthy glomeruli will prevent the filtration of proteins into the urine).

GFR can be assessed to determine if there is any renal failure. Biopsy can verify the type and severity of the problem.

Front 43

In diabetes insipidus a deficiency of ______ results in the excretion of excessive volumes of water for which the dog compensates by drinking more.

Back 43

ADH (Anti-diuretic Hormone)

Front 44

How is diabetes insipidus usually diagnosed?

Back 44

PU/PD.

Water deprivation test followed by giving ADH.

Front 45

You suspect a dog has diabetes insipidus and so do a water deprivation test, then give ADH. How can you determine if it is central or renal?

Back 45

Central: Urine will concentrate after administration of ADH.

Renal: Urine will NOT concentrate after administration of ADH.

Front 46

Case: 6 month old boston terrir female. PUPD. Urine is not concentrated. After a urine deprivation test, urine does not concentrate. After giving ADH, urine concentration increases. What is wrong with the dog?

Back 46

The dog has CENTRAL diabetes insipidus.