PU/Pd and conc disorders Flashcards
What is pollakiuria?
frequent passing of urine (not the same as polyuria)
What is nocturia?
urinating at night
What factors affect water intake?
Ambient temp
Respiratory evaporative loss
Exercise level
Water content of food
Faecal water content
Age
Physiological state e.g., pregnancy
What is the exception to PD coming after PU?
psychogenic polydipsia (PP) - excess drinking is behavioural issue => secondary polyuria
What are the most common causes of PU/PD in dogs and cats
Renal insufficiency, chronic renal disease
Diabetes mellitus
HAC (dog)
Hyperadrenocorticism (cats)
Describe the causes of primary polyuria
Central diabetes insipidus
Primary nephrogenic diabetes insipidus
Secondary nephrogenic diabetes insipidus
describe central diabetes insipidus
the pit gland does not release enough ADH due to hypothalamus or pituitary problem
How do you test for central diabetes insipidus?
Synthetic ADH => urine concentration increases
What is the treatment of central diabetes insipidus
Desmopressin = ADH agonist
maximises low levels of ADH
What is nephrogenic diabetes insipidus?
Kidney does not respond normally to ADH
Primary/congenital diabetes insipidus - aquaporin insertion defect
Secondary/acquired nephrogenic diabetes insipidus:
- variety or renal/metabolic conditions which interfere with normal ADH action
- affects renal tubular function
- or decreases hypertonicity of medullary interstitium => loss of conc gradient
What are the mechanisms for renal insufficiency causing PUPD?
Osmotic diuresis in remnant nephrons
Disruption of medullary architecture
Loss of medullary hypertonicity
Decreased functional nephrons
Describe how HAC causes diabetes insipidus
Causes PU/PD by defective ADH release - central diabetes insipidus
Impaired tubule response to ADH action - nephrogenic diabetes insipidus
How does hypoadrenocorticism cause PU/PD?
loss of osmotic gradient in renal medulla due to chronic Na wasting => loss of renal medullary hypertonicity => inadequate urine conc
How does hyperthyroidism cause primary polyuria?
thyrotoxicosis => increased CO and GFR and increased renal medullary blood flow, has potential to decrease renal medullary hypertonicity and urine concentrating ability
Same cats with hyperthyroidism may have primary polydipsia secondary to the effects of high thyroid hormone concs on the thirst centre
How does liver disease cause PU/PD?
due to loss of medullary hypertonicity
Liver disease => decreased production of urea => decreased renal medullary hypertonicity
Increased levels of corticosteroids inhibit the release of ADH => central diabetes insipidus
