NON-PROTEIN NITROGEN COMPOUNDS Flashcards
pair of grandular organs located at the retroperitoneal space
KIDNEYS
slightly lower than the other; adjacent to the liver
right kidney
FUNCTIONS OF THE KIDNEYS
- Excretory function
- Regulatory function
- Endocrine function
eliminates wastes and excess inorganic substances via urine formation
Excretory function
play a major role in homeostasis (balance)
Regulatory function
mechanism of differential reabsorption and secretion in the renal tubule
Regulatory function
Primary Endocrine function
:
production of hormones
Secondary Endocrine function:
degradation of insulin, glucagon and aldosterone
Urine formation
Glomerular filtration
Tubular reabsorption
Tubular secretion
substances are excreted out in the urine
Tubular secretion
substances are transferred from renal tubule to the circulation (ex. electrolytes: sodium - major extracellular cation)
Tubular reabsorption
- major extracellular cation
sodium
– absence of urine output; kidney failure
anuria
urine production diminishes – accumulation of [?]
metabolic waste
maintenance of which substances in the circulation
electrolytes
glucose
amino acids
water
maintenance of substances and pH in the circulation
homeostasis
the kidneys are capable of regulating these processes
mechanism of differential reabsorption and secretion in the renal tubule
– tuft of capillaries
glomerulus
– enclosing the glomerulus
bowman’s capsule
other parts:
renal tubules, ascending/descending loop of Henlee, PCT, DCT
– surrounding the tubules
peritubular capillaries
– hormone that regulates blood pressure
Renin
Renin-Angiotensin-Aldosterone System
Primary
– milk-curdling enzyme produced by neonates
Rennin
similar to pepsin in adults
Rennin
– hormone-like behavior; responsible for pain and muscle contraction (ex. tooth-ache)
Prostaglandin
– prevents production of prostaglandin, relieving pain
Analgesic
- hormone that regulates the production of rbc
Erythropoietin
– action of the hormone is targeted to a particular organ so that a specific process is stimulated and eventually degraded
Target organ
Not protein but has nitrogen in their structure
Most of them are used to evaluate renal function
Derived from the catabolism of proteins and nucleic acids
Clinically significant NPN cpds:
- urea – 45%
- amino acids – 20%
- uric acid – 20%
- creatinine – 5 %
- creatine – 1-2 %
- ammonia – 0.2%
important metabolytes; undergo reabsorption
- amino acids
- creatine
for protein production
amino acids
for energy metabolism
creatine
found in skeletal muscles
creatine
Nitrogen in a protein-free filtrate (a specimen) is converted to NH3 (ammonia) using hot H2SO4 (sulfuric acid)
KJELDAHL DIGESTION
Nessler’s reagent –
double iodide salt of potassium & mercury
– yellow to orange brown product
Dimercuric ammonium iodide
BERTHELOT METHOD
Reactant:
Reagent:
Catalyst:
Product:
NH3
phenol and alkaline hypochlorite
sodium nitroprusside (sodium ferricyanide)
indophenol blue
Modification by Searcy: using [?] (less toxic; used in the production of aspirin) instead of phenol
salicylic acid
MONITORING CONSUMPTION OF AMMONIA
Reaction:
Catalyst:
NH3
Glutamate dehydrogenase
Measure a decrease in the absorbance at 340 nm
MONITORING CONSUMPTION OF AMMONIA
Most abundant NPN compound
UREA
Major nitrogen-containing product of protein catabolism
UREA
Cycle
Krebs Henseleit Cycle
– removal of the amino group
Deamination
in retained in low conc in the circulation
Ammonia
~90% is excreted through the kidney
UREA
– only body fluid with very high conc of urea
Urine
Small amount is excreted through [?] and degraded by bacteria in the intestines
sweat
– body fluid with very low conc of urea
Sweat
– enzyme produced by bacteria to yield ammonia
Urease
– odor of urine due to bacteria
Ammoniacal
freely filtered through the
glomerulus
undergo tubular reabsorption
40 to 70%
– preferred than creatine for renal function tests
Creatinine
Amount of urea reabsorbed is dependent on
urine flow rate
: clearance of urea is proportional to the GFR
Rapid flow rate
- ↓tubular reabsorption
RAPID
- ↑reabsorption
SLOW
Dehydration/↓Water
SLOW
- ↑excretion in urine
RAPID
- ↓exretion
SLOW
- ↑ clearance of urea
- ↑ GFR
RAPID
- ↑blood urea nitrogen
SLOW
BUN is not reliable to monitor renal function because:
It is affected by the [?]
Largely affected by [?]
Large amount is [?]
body’s state of hydration
protein intake and catabolism
reabsorbed in renal tubules
is specific but not sensitive
BUN
- enzymatic
BUN
Measurement of ammonia from urea
BUN
- non-enzymatic
UREA
Measurement of urea
UREA
stability of urea in serum
up to 24 hrs at RT
several days at 2 to 6 C
2 to 3 mons. when frozen
inhibits urease enzyme
Fluoride and Citrate
contraindicated in the assay
Double oxalate (ammonium potassium oxalate)
Prolonged standing: [?] due to deamination
2 to 3x increase in NH3 conc
does not interfere
Lipemia and hemolysis
is not required
Fasting sample
Based on the preliminary hydrolysis of urea with urease
INDIRECT/ENZYMATIC
Quantitation of ammonium ion liberated
INDIRECT/ENZYMATIC
Measurement of BUN
INDIRECT/ENZYMATIC
NH4 reacts w/ phenol & hypochlorite
BERTHELOT REACTION
BERTHELOT REACTION
Product:
Indophenol (blue)
NESSLERIZATION
Product:
yellow to orange product
Beckman BUN Analyzer
CONDUCTIMETRIC METHOD
Based on the conductivity generated when NH4 ions & HCO3 are produced from the reaction of urease on urea
CONDUCTIMETRIC METHOD
Reaction is monitored by a conductivity electrode
CONDUCTIMETRIC METHOD
Based on chromatography
URASTRAT STRIP METHOD
Serum or plasma travels up the urastrat strip (by capillary action)
URASTRAT STRIP METHOD
URASTRAT STRIP METHOD
Reactants:
Urease, K2CO3 BCG (bromcresol green) - tartaric acid
URASTRAT STRIP METHOD
Product:
Blue color
BUN mg/dL (30 mins.)
URASTRAT STRIP METHOD
URASTRAT STRIP METHOD
Formula
Height of color change (mm) x 5 + 10
DIACETYL MONOXIME (DAM)
Reference:
Fearon
Diacetyl monoxime hydrolyzes in the presence of acid to produce
diacetyl (unstable)
Diacetyl reacts w/ Urea to produce a
diazine derivative (pink / yellow)
DIACETYL MONOXIME (DAM)
Product
diazine derivative (pink / yellow)
Adaptable to autoanalyzers
DIACETYL MONOXIME (DAM)
Reaction is highly specific
DIACETYL MONOXIME (DAM)
– a biochemical abnormality pertaining to increase NPN compounds (Creatinine & Urea) defining GFR defect
AZOTEMIA
– increased plasma urea concentration
UREMIA
: related to renal circulation defect
a. Pre-renal
Congenital Heart Failure, shock, hemorrhage, dehydration, hypovolemia
a. Pre-renal
Increase in urea w/o an increase in creatinine
a. Pre-renal
: defect GFR
Renal
lesions along renal parenchyma
Renal
Acute glomerulonephritis (AGN)
Chronic nephritis
Polycystic kidney disease
Tubular necrosis
Renal; Post-renal
Renal; Post-renal
Renal; Post-renal
obstruction of urine flow
Post-renal
– presence of renal calculi or kidney
Nephrolithiasis
males
Prostatitis
Nephrolithiasis
Prostatitis
Tumors of the genitourinary tract
c. Post-renal
BUN : CREATININE RATIO
NORMAL:
10-20:1 (8 to 20 mg/dL – conventional)
BUN : CREATININE RATIO
Conversion factor =
0.357
Acute tubular necrosis (↓reabsorption)
BUN:CREA ratio <10
Low protein intake; starvation
BUN:CREA ratio <10
Severe liver disease
BUN:CREA ratio <10
Repeated dialysis
BUN:CREA ratio <10
Severe vomitting or diarrhea
BUN:CREA ratio <10
Catabolic states w/ tissue breakdown
BUN:CREA ratio >10:1 with normal creatinine
Pre-renal azotemia
BUN:CREA ratio >10:1 with normal creatinine
High protein intake
BUN:CREA ratio >10:1 with normal creatinine
After GIT hemorrhage
BUN:CREA ratio >10:1 with normal creatinine
Post-renal obstruction
HIGH RATIO WITH ELEVATED CREATININE LEVELS
Pre-renal azotemia superimposed on renal disease
HIGH RATIO WITH ELEVATED CREATININE LEVELS
