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Flashcards in Renal CVT Deck (408)
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1

Define PU/PD

urine output > 50 ml/kg/day or water consumption > 100 ml/kg/day

2

Where is ADH synthesized and stored?

ADH synthesized in supraoptic and paraventircular nuclei of hypothalamus, stored in pituitary

3

What is another name for ADH?

Anti-diuretic hormone = Vasopressin

4

What stimulates ADH release?

ADH releases when decrease in plasma osmolality, arterial hypotension, fever, pain, nausea, hypoglycemia, exercise, certain drugs

5

How does ADH work?

○ In distal convoluted tubule and collecting duct ADH stimulates passive resorption of solute-free water (without ADH these areas are impermeable to water)
○ ADH binds to V2 receptors leading to insertion of aquaporin-2
○ Channels allow water to flow along osmotic gradient between distal convoluted tubule/collecting duct and the hypertonic renal medulla

6

What are 3 physiologic processes that allow for concentration of urine?

○ Concentration of urine in the presence of ADH
§ PROBLEM: Reduced production of ADH
○ Ability of renal tubules to respond to ADH
§ PROBLEM: Inability to respond to ADH
○ Presence of osmotic gradient btwn hypertonic renal medulla and fluid in distal convoluted tubule and collecting duct
§ PROBLEM: Osmotically active substances in urine filtrate or decreased medullary hypertonicity

7

Name 6 conditions that can result in primary polydipsia.

1. Behavioral Problem (pyshcogenic)
2. Hyperthyroidism (cats)
3. Primary GI disease (dogs)
4. Hepatic encphalopathy
5. Hyperadrenocorticism
6. Fever
7. Pain

8

How can serum [Na+] help in determingin primary PU vs primary PD?

○ Sometimes can tell from Na+ or measured osmolality
§ [Na+] at or below RR → Primary polydipsia
□ Can also be related to hypovolemia
§ [Na+] above RR → Primary polyuria
□ NOT helpful it normal Na+

9

What is the percentage of functional renal mass results in loss of concentrating ability?

66%

10

What is the percentage of functional renal mass results in azotemia?

75%

11

What is central diabetes insipidus?

§ Deficiency in ADH (may be partial or complete)
□ Trauma, neoplasia, congenital defects, idiopathic
§ Patient cannot produce concentrated urine in response to water deprivation but responds to exogenous ADH

12

What is primary nephrogenic diabetes insipidus?

§ Rare congenital → Renal tubules are unable to respond to ADH
§ Animals cannot concentrate urine in response to water deprivation or administration of exogenous ADH

13

What is secondary nephrogenic diabetes insipidus?

§ Main cause in dogs and cats, usually primary polyuria and secondary polydipsia
§ Acquired inability of renal tubules to respond to ADH (related to loss of medullary gradient or interference of action of ADH)
§ No use for water deprivation test

14

What are the 4 major mechanisms of secondary nephrogenic diabetes insipidus?

1. Osmotic diuresis
2. Loss of medullary hypertonicity (medullary washout)
3. Impaired tubular response to ADH
4. Downregulation of aquaporin-2

15

What is renal medulally solute washout?

§ Fluid therapy, diuretics, and chronic PU/PD can all lead to this → Lead to impair renal response to ADH

16

What are the most common causes of PU/PD in dogs?

CKD, Hyperadrenocorticism and diabetes mellitus

17

What are the most common causes of PU/PD in cats?

CKD, diabetes mellitus, hyperthyroidism

18

What are the ranges for minimally concentrated urine?

1.013-1.030 (dog) and 1.013-1.040 (cat)

19

Name 3 methods to assess GFR?

iohexol clearance, exogenous creatinine clearance, and nuclear scintigraphy

20

What is DDAVP?

§ Desmopressin (synthetic analog of ADH)
§ When to consider it: All other steps complete and ruled out all causes of secondary NDI, historical information and [Na+] more consistent with CDI, close monitoring and free access to water
□ Look for either drop in water intake or increased USG → CDI
® NOTE: Animals with HAC will also have a positive response!!!

21

What diseases can result in a positive response to a DDAVP?

CDI, and hyperadrenocorticism

22

What is the mechanism of PU/PD in diabetes mellitus?

Secondary NDI
Osmotic diuresis

23

What is the mechanism of PU/PD in primary renal glucosuria?

Secondary NDI
Osmotic diuresis

24

What is the mechanism of PU/PD in Fanconi syndrome and other tubulopathies?

Secondary NDI
Osmotic diuresis

25

What is the mechanism of PU/PD in Chronic renal failure?

Secondary NDI
Osmotic diuresis

26

What is the mechanism of PU/PD in polyuric acute renal failure?

Secondary NDI
Osmotic diuresis

27

What is the mechanism of PU/PD in postobstructive diuersis?

Secondary NDI
Osmotic diuresis
Downregulation of aquaporin-2

28

What is the mechanism of PU/PD in chronic partial ureteral obstruction?

Secondary NDI
Downregulation of aquaporin-2

29

What is the mechanism of PU/PD in renal medullary solute washout?

Secondary NDI
Decreased renal medullary tonicity with loss of osmotic gradient

30

What is the mechanism of PU/PD in pyelonephritis?

Secondary NDI
Bacterial endotoxin reduced tubular sensitivity to ADH
Damaged countercurrent mechanism