Flashcards in Renal CVT Deck (408)
urine output > 50 ml/kg/day or water consumption > 100 ml/kg/day
Where is ADH synthesized and stored?
ADH synthesized in supraoptic and paraventircular nuclei of hypothalamus, stored in pituitary
What is another name for ADH?
Anti-diuretic hormone = Vasopressin
What stimulates ADH release?
ADH releases when decrease in plasma osmolality, arterial hypotension, fever, pain, nausea, hypoglycemia, exercise, certain drugs
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
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
Name 6 conditions that can result in primary polydipsia.
1. Behavioral Problem (pyshcogenic)
2. Hyperthyroidism (cats)
3. Primary GI disease (dogs)
4. Hepatic encphalopathy
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+
What is the percentage of functional renal mass results in loss of concentrating ability?
What is the percentage of functional renal mass results in azotemia?
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
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
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
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
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
What are the most common causes of PU/PD in dogs?
CKD, Hyperadrenocorticism and diabetes mellitus
What are the most common causes of PU/PD in cats?
CKD, diabetes mellitus, hyperthyroidism
What are the ranges for minimally concentrated urine?
1.013-1.030 (dog) and 1.013-1.040 (cat)
Name 3 methods to assess GFR?
iohexol clearance, exogenous creatinine clearance, and nuclear scintigraphy
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!!!
What diseases can result in a positive response to a DDAVP?
CDI, and hyperadrenocorticism
What is the mechanism of PU/PD in diabetes mellitus?
What is the mechanism of PU/PD in primary renal glucosuria?
What is the mechanism of PU/PD in Fanconi syndrome and other tubulopathies?
What is the mechanism of PU/PD in Chronic renal failure?
What is the mechanism of PU/PD in polyuric acute renal failure?
What is the mechanism of PU/PD in postobstructive diuersis?
Downregulation of aquaporin-2
What is the mechanism of PU/PD in chronic partial ureteral obstruction?
Downregulation of aquaporin-2
What is the mechanism of PU/PD in renal medullary solute washout?
Decreased renal medullary tonicity with loss of osmotic gradient