Polyuria & Polydipsia Flashcards
What are the 4 steps to urine formation?
- filtration of plasma through glomerulus
- reabsorption
- secretion
- excretion
What is the greatest contributor to the urine concentration gradient?
urea
How does the pituitary gland control water absorption and urine concentration?
- releases ADH in response to an increased plasma osmolarity (sodium, glucose) or low ECF volume
- ADH enhances water permeability, causing it to be passively absorbed along the osmotic gradient
- this results in more concentrated urine
At what USG is urine considered normally concentrated by the renal tubules?
- DOGS = > 1.030
- CATS = > 1.035
(always analyze with Hx of the patient!)
What amount of water intake is necessary for maintenance? What is considered polydipsia?
50-60 mL/kg/day, based on insensible loss caused by breathing or urine excretion
drinking 2x the maintenance —> 100 mL/kg/day
What is the normal amount urine expected to be produced in a day? What is polyuria?
~ 40 mL/kg/day
excessive increase in urination with increased volumes
What is the difference between polyuria and pollakiuria?
POLYURIA - excessive and increased volume
POLLAKIURIA - excessive urination in small amounts (sign of LUT disease)
ASK CLIENTS about size of puddles, frequency, duration, urine stream, or litter box clumps
What are 3 causes of primary polyuria with compensatory polydipsia?
- lack of ADH
- lack of response to ADH
- lack of medullary concentration gradient
What are 3 causes of primary polydipsia with compensatory polyuria?
- physiologic
- behavioral
- pathologic
(psychogenic due to brain tumors or head trauma)
What is central diabetes insipidus?
lack of ADH release due to pituitary disease
What is nephrogenic diabetes insipidus?
lack of response to ADH most commonly caused by substances that interfere with ADH binding to receptors in kidneys
- bacterial endotoxins: E. coli from pyelonephritis, pyometra, or prostatitis
- calcium
- cortisol
What are 3 causes of of loss of medullary concentration gradient?
- hyponatremia, hypokalemia, or decreased BUN, which decreases the osmolality of plasma
- osmotic diuresis - diabetes mellitus or renal glucosuria, where glucose in filtrated urine pulls water
- reduced nephron function - chronic renal failure
What are some disease pathways that lead to primary polyuria?
- central and nephrogenic diabetes insipidus
- endotoxins from pyometra, pyelonephritis, and prostatitis
- hyperadrenocorticism, hypercalcemia: cortisol and calcium block renal receptors for ADH
- DM, renal glucosuria: osmotic
- hypoadrenocorticism: decreased aldosterone causes hyponatremia
- hyperthyroidism: increased renal blood flow
- chronic renal disease: damage to kidneys
- leptospirosis: tubular damage
What are the most common causes of PU/PD in dogs and cats?
DOGS: CKD, hyperadrenocorticism (Cushings), DM
CATS: CKD, hyperthyroidism, DM
How can we ask clients to quantify water intake?
- fill water bowl as normal, measuring total water volume
- refill bowl as needed through the next 24 hours while measuring each refill
- quantify the amonut of water left and subtract it from the total volume