Renal Flashcards
4 major processes in the nephron
- Glomerular filtration
- Tubular resorption
- Tubular secretion
- Water regulation
What does GFR depend on?
- renal blood flow
- Number of functional nephrons
- Hydrostatic pressure
Rate substances are cleared from plasma via glomerular
Osmolality
Concentration of solutes per kg of water
Osmometer
Measures number of particles in a volume of water
Not convenient but more accurate
Urine specific gravity
Refractometer is convenient but less accurate, Depends on particle weight and how each particle bends light
Prone to interference
Getting osmolality from USG
Multiply the last two digits by 30
Rough estimate
ADH
Made in hypothalamus and secreted by posterior pituitary. Opens water channels via aquaporin proteins
Stimulation of ADH secretion
-Plasma hyperosmolality
-Decreased cardiovascular pressure
Result of ADH
Conserve body water to decrease plasma osmolality and increase blood volume
Major events in the proximal CT
Removes volume but no change in concentration
Major events in the Descending LOH
Removes H2O and increase concentration
Major of events of the ascending LOH
Removes solute
Dilution due to decreased concentration
Major events of the distal nephron
Removes H2O and increases concentration
What is needed to produce concentrated urine
- Adequate # of nephrons
- Adequate ADH
- Distal nephron is responsive to ADH
- Hypertonic interstitium in the renal medulla (Urea, Na, Cl)
What happens to the expected values of USG in dehydrated animals
Dog> 1.030
Cat> 1.35
Horses and cattle> 1.025
Isosthenuria
Urine osmolality and plasma osmolality are equal. In dehydrated pt means kidneys have not concentrated nor diluted the tubular fluid (1.007-1.013)
Hyposthenuria
Urine osmolality < plasma osmolality.
in dehydrated pt, Kidneys have not actively diluted the tubular fluid. Not renal failure (1.006)
Pollakiuria
Increased frequency of urine but doesn’t indicate urine volume
Ways to assess GFR
-Urea nitrogen
-Serum creatinine
-SDMA ( not as common)
Ways to asses integrity of glomerular structure
-Urine protein
-Urine protein: urine creatinine ration
Ability of renal concentration and dilute urine
-USG (compare urine and plasma osmolality)
-Water deprivation test
Urinalysis assessment
-USG
-Chemistry
-Sediment examination
Assesses more than urinary tract
Azotemia
Increased concentration of Urea unitrogen (BUN or UN) and or creatinine
Increased urea formation
-High protein diet
-GI hemorrhage
-Disorders that increase endogenous protein catabolism
Decreased urea formation
-Hepatic failure/shunt
-Malnutrition
-Diuresis
Alternate routes of UN for rumenants and horses
Saliva, sweat, GI tract
UN is not a sensitive indicator of GFR in those species
Important contribution by urea
Easily diffuses across most cell membranes and contributes the renal medullary concentration gradient and drives recovery of water/ concentration of urine in the collecting ducts
Measuring urea nitrogen
Serum (red top) or plasma (green top)
What is creatinine
Waste product from normal breakdown. Excreted in urine and not resorbed by tubules. The amount formed daily is constant for a given animal. May be proportional to muscle mass
Increased Creatinine
Does not mean increased muscle catabolism
-Decreased GFR
Decreased creatinine
May not be clinically significant(needs to be really really low)
-Decreased muscle mass
-Hypoproteinemia
UN and creatinine in dogs and cats
UN and creatinine increase in parallel when GFR is decreased from renal failure
UN and creatinine mismatch in dogs and cats
-Prerenal azotemia-> greater increase in UN
-GI hemorrhage-> increased UN
-Anorectic or low protein diet-> decreased UN
-Extremely cachectic-> decreased creatinine
Horses and ruminants UN and creatinine
Creatinine more specific for renal compromise due to alternate urea metabolism by bacteria
