Clinical Pathology Of Urinary System Flashcards
Functions of kidney
• Urine production - elimination of metabolic wastes
• Acid-base regulation
• Conservation of water
• Maintenance of normal extracellular potassium concentration
• Endocrine functions
– Erythropoietin
– Renin
– Vitamin D
3 major processes control renal excretion of H2O and solutes
• Glomerular filtration
– Filtration of a substance depends on molecular size and electrical charge (e.g albumin)
• Tubular resorption
• Tubular secretion
Consequences of impaired renal function
• retention of metabolites that are normally removed by healthy kidneys
• indices of diminished renal function
– plasma or serum concentrations of urea and
creatinine to get idea of kidney function
• Elevated urea and/or creatinine described as AZOTEMIA
• Impaired urine concentrating ability
Azotemia
Elevated urea and/or creatinine
What is used to assess renal function
Urinalysis- a dipstick that measures protein, blood, glucose, ketones, pH of urine
Ways to collect urine
• Voided / free catch
• Catheter
• cystocentesis
Urine specific gravity (USG)
-what is it
-what is used to give an index of specific gravity
-large amounts of what will increase USG?
• ratio of a solutions weight to the weight of an equal volume of distilled water
• Refractive index is used to give an estimate of USG
-large amounts of glucose or albumin
Hyposthenuria
-meaning
• urine osmolality < isosthenuric values
• diluted urine
• S.G. 1.001 – 1.007
Isosthenuria
-meaning
-specific gravity
Specific gravity is 1.008 – 1.012
urine osmolality = plasma osmolality
Hypersthenuria
-meaning
• excretion of highly concentrated urine (rarely used term)
Regulation of body water
-in healthy animals
-maximal urine dilution S.G in domestic animals;
Healthy animals with normal or adequate renal function can excrete urine with a broad USG range depending on what the kidneys are challenged to do
Maximal urine dilution in domestic species near 1.001
Maximal urine conc of
Cat
Dog
Horses/cattle
Cat
>1.080
Dog
>1.060
Horses/cattle
>1.050
Best predictor of urine function;
GFR
Ideal solute for measuring GFR has what features
• Not be protein bound
• Pass freely through filtration barrier
• Neither be secreted nor resorbed by tubules • Various substances available
• But Expensive
Another protein used to measure kidney function and it’s features
CREATININE:
-Protein we can measure in blood
-product of creatine degradation in muscles
• Passes freely through glomerular filtration barrier
• Not resorbed by the tubules
• Rate of production depends on muscle bulk and turnover
Another measurement of kidney function; urea
Synthesis occurs in hepatocytes via urea cycle
• Method of excreting excess ammonium
• Kidney excretes most
• Not reliable in cattle
• Urea enters the rumen and Used for AA production
Increased creatinine is seen with…
– Decreased urinary excretion, which is seen with;
• Dehydration
• Renal dysfunction
• Outflow obstruction
– High muscle mass
• greyhounds
• bulls
Causes for increased urea
nonrenal causes for ^ urea
– Decreased urinary excretion
• Dehydration, hypovolaemia
• Renal dysfunction
• Urinary outflow obstruction
– Nonrenal causes
• High protein diet
• Increased muscle breakdown
• GI bleeding
Azotemia vs Uraemia
• Increased non-protein nitrogenous compounds in the blood (we measure elevated urea and creatinine)
• Clinical syndrome reflecting renal failure
– Vomiting, diarrhoea, breath that smells of ammonia
Classification of azotemia
-3 different types
• Prerenal- problems occuring before reaching kidney
• Renal- problems within kidney
• Post renal- problem further down urinary tract
True or false more than one type of azotemia may occur at once
True
Symptoms of prerenal azotemia
-accompanying USG in
Dog
Cat
Horses/cattle
• Dehydration
• Hypovolaemia
• Decreased cardiac output
– Dog >1.030
– Cat >1.035
– Horses/cattle >1.025
Renal azotemia
-what is it
-causes
-accompanying USG
Any renal disease with enough glomerular damage to cause a major decrease in GFR
• Loss of 65-75% of nephron functional capacity —> decreased GFR
• Inadequate renal excretion of urea and crt
• Accompanying USG 1.008-1.012 Isosthenuria
Post renal azotemia
Caused by…
• The initiating cause of abnormal urea and crt is distal to the nephron
• caused by Urinary tract obstruction
– Release of vasoactive substances
– Glomerular arteriole constriction
– decreased RPF and GFR
– Transient intracapsular hydrostatic pressure – Less ultrafiltrate formed
• Urine leakage into abdomen
– Passive absorption into plasma from peritoneum
• May be anuric
What do kidneys do when a patient is dehydrated
Kidneys want to conserve water so produce highly concentrated urine- USG will be highly concentrated
What does SDMA stand for
-what is it
-released during what
-useful for…
Symmetric Dimethylarginine
• Small molecule formed by methylation of arginine
• Released during protein degradation
• Useful for early identification and monitoring of chronic kidney disease (dogs/cats)
• Limited availability - Idexx
Inorganic phosphate
• Skeletal mineral
• Important intracellular ion
– Enzyme cofactor, phosphorylation reactions
• Calciumandphosphorushomeostasisare
interdependent (see renal secondary hyperparathyroidism)
• Markedly decreased GFR in renal failure does what to renal excretion of phosphate
• Markedly decreased GFR in renal failure decreases renal excretion of phosphate—> leads to hyperphosphataemia
Calcium
-type of mineral
-functions
-renal failure causes…
• Skeletal mineral
– Muscular contraction, blood clotting, enzyme
function
• Renal failure – may see normo-, hypo- or hypercalcaemia in cats and dogs
• Hypercalcaemia of paraneoplastic syndrome
Rubber jaw
-cause by
Minerals removed from bone so bone becomes soft
Potassium
-main route of excretion is through…
• Kidney is main route of excretion of excess Potassium from the body
• Hyperkalaemia
– Anuria or oliguria (e.g. ARF)
• Decreased flow of tubular fluid in nephron
– Reduced renal blood
flow
Hyperkalaemia and hypokalaemia
Higher than normal potassium levels in the blood.
Lower than normal
Albumin
Nephrotic syndrome
Proteinuria
-how to measure it
-possible causes
Using “stix”
– Sensitive to albumin
– Alkaline urine may give false positive (herbivores)
Haemorrhage, Leucocytes (inflammation), renal disease
Urine protein:creatinine ratio
• More accurate measurement of urine protein
Take a blood sample and look at ratio of the two
• <0.2 normal, 0.2-0.5 (dog) and 0.2-0.4 (cat) equivocal, >than this abnormal
• Consider sediment contents before interpretation
– Active sediment e.g. haemorrhage, inflammation make P:C ratio unreliable
Renal failure
Decreased GFR (but this may be caused by other things so bear in mind)
• Pre-renal, renal, post-renal
• Acute vs chronic
With renal failure you Must lose significant portion of the kidney before seeing clinical effects
