11) Nonprotein nitrogen and renal function Flashcards
urinary filtrate flow
Bowman’s capsule
Proximal convoluted tubule (PCT)
Descending loop of Henle
Ascending loop of Henle
Distal convoluted tubule (DCT)
Collecting duct
Renal calyces
Ureter
Bladder
Urethra
renal blood flow
Renal artery
Afferent arteriole
Glomerulus
Efferent arteriole
Peritubular capillaries
Vasa recta
Renal vein
large, ——- charged molecules are repelled by the —– charge of the basement membrane
negatively
negative
renal threshold
Concentration above which the substance cannot be totally reabsorbed and is excreted in the urine
always reabsorbed through passive transport
water
urea
2 major functions of tubular secretion
- Elimination of waste products not filtered by the glomerulus
- Regulation of acid-base balance in the body through secretion of H+
nonprotein nitrogen
Comprises the products of catabolism of proteins and nucleic acids, which contain nitrogen but are not part of a protein molecule
most clinically significant NPN in plasma
BUN
amino acids
uric acid
creatinine
creatine
ammonia
3 NPN sources in highest amount
Blood urea nitrogen (BUN)
Amino acids
Uric acid
Major nitrogen-containing metabolic product of protein catabolism in humans
urea/BUN
Approximately —% of NPN is eventually excreted
75
In a patient with a normal to increased GFR, approximately –% of the BUN is reabsorbed and –% is excreted.
40
60
In a dehydrated patient, –% of the BUN is reabsorbed and –% is excreted.
70
30
3 variables BUN depends on
Urea concentration
Glomerular filtration rate
Level of hydration
azotemia
- An increased blood urea and other NPN compounds
- No external symptoms
uremia
- An increased BUN
- More severe, now showing sx (n/v, fatigue, HTN, anorexia, uremic frost)
uremic frost
3 categories of azotemia
prerenal
renal
postrenal
normal BUN:creatinine ratio
10:1 to 20:1
normal BUN:Cr ratio
renal disease
elevated proportionally
prerenal azotemia BUN:Cr
> 20:1 to 30:1
postrenal azotemia or prerenal + renal azotemia BUN:Cr
high ratios with elevated Cr
Berthelot’s reaction
BUN method
sodium nitroprusside
BUN method
Nessler’s rxn
BUN method
glutamate dehydrogenase (GLDH) procedure
BUN method
Diacetyl or Fearon Reaction
BUN method
BUN RR
7-18 mg/dL
BUN is stable at room temp for —- hours, ——– refrigerated, and —– months frozen
24 hours
several days
2-3 months
B U N <8-10 mg/dL
overhydration
BUN 50-150 mg/dL
impaired GFR
BUN 150-250 mg/dL
severe renal impairment
convert from urea to urea nitrogen
BUN = 28 g/mol
urea = 60 g/mol
creatinine synthesized in liver from…
Arginine
Glycine
Methionine
creatinine
Waste product derived from creatine and creatine phosphate which is contained in the muscle