non protein nitrogen Flashcards
what is the purpose of determining non-protein nitrogen in the blood
monitor renal funciton
what causes the formation of most NPN compounds
protein catabolism releasing nitrogen which is converted to ammonia
blood urea nitrogen (BUN)
highest concentration of NPN
product of protein catabolism
reabsorbed in nephron tubules
where in the liver is BUN at highest concentration
collecting duct and ascending arm
what does BUN reabsorption depend on
flow rate and hydration in ascending arm
azotemia
elevated concentration of urea in blood (high BUN)
- very high associated with uremia or uremic syndrome (renal failure)
three causes of urea plasma elevation
- prerenal: issues with heart (systolic or diastolic) causing less blood flow to kidney
- renal: issue with kidney itself
- postrenal: generally urine back up into the kidney
prerenal azotemia
less blood to kidney causes less urea filtration
renal azotemia
defintion and disease states related
decreased renal function causes increased blood urea due to poor excretion
- acute/chronic failure
- glomerular nephritis (bowmans burst from pressure)
- tubular necrosis (lack if O2)
what can cause decreased urea nitrogen
low protein, liver disease, severe vomiting, increased protein synthesis
how is BUN measured
urea reported in terms of nitrogen byt measuring NADH-NAD conversion
how are BUN and NADH conversion related
inversely proportional
where is creatine synthesized
in liver
how are creatine, creatine phosphate and creatinine related
- creatine can be converted to creatine phosphate via creatine kinase
- creatine can be converted to creatinine by loss of water
- creatine phosphate can be converted to creatinine by loss of phosphoric acid
what is creatine/creatinine used to measure
kidney biomarker
creatinine life cycle
- released in proportion to muscle mass (stable)
- filtered by glomerulus
- excreted in urine
disease correlations of creatinine
elevated creatinine is found with abnormal renal function -> lowered glomerular filtration rate
how is glomerular filtration rate (GFR) measured
GFR = V/t
V= plasma filtered
t= time
what is creatinine clearance
measurement of amt creatinine eliminated from blood by kidneys per unit of time
- plasma concentration of creatinine is inversely proportional to clearance
- increased plasma lvls of creatinine decrease GFR
creatinine clearence equation
(urine creatinine/plasma creatinine)(urine mL/minutes)(1.73/BSA)
what is the purpose of BUN:creatinine ratio
to determine where azotineal issue is coming from -> both filtered but BUN reabsorbed wherease creatinine is not
pre renal BUN:creatinine ratio
> 20:1
- BUM reabsorption increased
intrarenal BUN:creatinine ratio
<10:1
- reduced BUN reabsorption
postrenal/normal BUN:creatinine
10-20:1
- BUN reabsorption normal
uric acid
- a breakdown product of purine metabolism in the liver
- in plasma as monosodium urate
where is uric acid transported to
the kidney to be filtered
at what concentraiton of plasma monosodium urate do crystals precipitate
> 6.8mg/dL
urea is formed to neutralize the toxic effect of what waste product
ammonia
ammonia
comes from deamination of amino acids (protein catabolism), digestive biproduct and released from muscles during excerise
disease correlations with ammonia
- severe liver disease (not enough urea to convert to BUN to remove)
- encephalopathy: elevated ammonia
- reye’s syndrome: ammonia deposition from infants taking aspirin
