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What affects GFR?

Renal perfusion and plasma flow


Define azotaemia

- increase in non-protein nitrongenous compounds (usually urea nitrogen (UN) and or creatinine or uric acid (birds)) in the blood


Define uraemia?

Uraemia = sick from azotaemia (every urea mic animal is azotaemic but NOT vice versa)


Clinical signs of uraemia

- anorexia
- VD+
- GI haemorrhage
- ulcerative stomatitis
- bruxism in ruminants


What causes loss of kidney function?

Loss of number of functioning nephrons (not a decrease function of each individual)


Which biochem parameters are related to renal function?

- UN
- creatinine
- phosphorus
- calcium
- sodium
- chloride
- potassium
- acid base
- protein


Which 2 diagnostics are more important for evaluating renal function?

Serum/plasma chemistry and urinalysis CONCURRENTLY


Most important biochem results

> UN (urea nitrogen)
> creatinine
- indicate GFR (^conc in blood if GFR v)


Where is urea produced and where does it travels?

- urea produced in liver from ammonia (ammonia very toxic, urea bit less toxic)
- excreted by kidney
- levels affected by liver function and protein levels


What affects creatinine levels

Derived from creatine in muscles, influenced by muscle mass


What causes ^ urea

Protein meal or decrased filtration (GFR)


Is urea excreted in feaces?



How does excretion of urea and creatinine differ?

Creatinine not reabsorption
- urea can reabsorb in collecting duct


Does urea equilibrate in body?

Once in vascular diffuses through body water in 90mins


How is UN excreted?

- Renal excretion most important route
- passively filtered by glomerulus (conc filtrate same as blood)
- passively diffuses with water from tubular luman back into blood
- amount absorbed inversely proportional to urine flow (v urine flow ^ absoroption and ^ blood levels)


Is Urea measurement reliable in ruminants ?

- NO (Use creatinine)
- cattle severe renal dz can compensate urea levels as excreted into rumen and used to produce protein
- if anorectiv all urea will be excreted via GIT not kidneys


Creatinine sources - what influences levels? How easily does this equilibrate?

- non-enzymatic conversion of creatine stores ini muscle
- constant rate of conversion (influenced by muscle mass and disease)
- will distribute in body water but very slowly cf. urea


How do creatinine and urea levels change with a ruptured bladder?

- abdo fluid concentrations creatinine > serum levels
- difference with serunm lasts longer cf. differneces in urea levels


Is creatinine a sensitive indicator of kidney function?

NO 3/4 nephrons lost before parameters change
- more sensitive cows and horse
- not at all sensitive birds


whY IS Creatinine such a poor indicator in birds ?

- uric acid produced instead
- hyperuriceamia does occour but not very sensitive
- may also occour during ovulation and after meal


3 types of azotaemia

> prerenal azotaemia
- v GFR d/t v renal perfusion (poor BP -> vasoconstriction and ULTIMATELY ischaemia)
- or ^ protein catabolism
> renal
- v GFR d/t non functioning nephrons
> postrenal
- interference with excretion of urine (obstruction/postrenal leakage)


How can prerenal azotaemia be Dx?

Urine SG low shows no functioning nephrons and poor concentration
- if urine SG normal then must be pre renal


Causes of prerenal azotaemia

- ^protein catabolism
- gastric or SI haemorrhage / necrosis / starvation / corticosteroids / high protein diet
- reduced renal perfusion == haemoconcentration MOST COMMON CAUSE
- dz causing pre/post renal azotaemia 2* affect the kidneys -> renal azotaemia
- USG high d/t ADH response occouring -> concentration of urine


Why dos USG increase with pre-renal azotaemia?

- ADH response -> kidney concentrates urine


Causes of Post renal azotaemia. CLinical signs?

- obstruction/post rental leakage
- oliguria/anuria clinically
- USG may vary
- UN and creatinine return to normal once obstruction releved


What is USG compared with?

Creatinine and urine on serum /plasma


What is USG and what is it a measure of?

- ratio of refractive index urine cf. ater
- depends on particle size, weight and number
- refractomter
- reflects osmolality (very expensive machine needed to measure this!)
- falsely increased by glucose and protein


What is a normal USG?

No reference interval
- based on expectation
- range 1.001 - 1.065 in healthy animals (1.080 in cats)
- concentrating ability neonates is poor


What may falsely increase USG?

- glucose (some effect on osmolality but not much)
- protein (no effect on osmolality but 3+ increase ~= 0.004 change)


With azotaemia, what should USG be?

- 1.03 dog
- 1.035 cat
- 1.025 horse or ruminant
> if less than these = decreased concentrating ability and renal failure