Quantification of Renal Function Flashcards
what do macula densa cells do?
sense changes in the volume delivery to the DT (senses the contents of the glomerular fluid)
when does erythropoietin get secreted?
in response to oxygen tension in the blood
metabolic function of the kidney
- activation of Vit D3
- gluconeogenesis
- metabolism of insulin, steroids, and xenobiotics (mostly in cortex)
secretion ___ impacts what ends up being in final product of urine
positively (positively impacts excretion)
Move in the direction of peritubular capillary blood to the tubular fluid
absorption ___ impacts what ends up being in final product of urine
negatively (negatively impact excretion)
tubular fluid → capillary blood
glomerular filtration
passive diffusion of water and SMALL molecules across glomerular capillary and into Bowman’s capsule and PT
What size proteins are too large to be filtered across glomerular capillary?
> 60 kDa
Large proteins get impeded and do not cross the glomerular capillary
secretion
active transport
occurs mostly in proximal tubule (anionic and cationic transporter syst are present and involved in the elimination of many drugs
anionic drugs that are secreted
probenicid, penicillin
cationic drugs that are secreted
creatinine, cimetidine, procainamide
which glycoproteins are involved in the elimination of cytotoxic drugs?
P-gp and multidrug resistance protein
where does drug reabsorption occur in the kidney?
along the distal tubule and collecting tubules
Intact Nephron Hypothesis
renal disease is the result of reduced number of appropriately functioning nephrons (remaining nephrons compensate for the diseased ones)
single nephron GFR (SNGFR) in renal disease
increases in the remaining nephrons and whole kidney GFR represents the sum of SNGFR of the remaining functional nephrons
s/sx of renal dysfunction
HTN, edema, electrolyte imbalance, anemia, increased urine output, metabolic acidosis (mild), bone demineralization, hyperkalemia, mental confusion, nausea, vomiting (from accumulated urea)
what are the 2 most important lab values for renal dysfunction?
BUN and SCr
how is urea made in the kidney?
AA → ammonia → urea
(prod of urea is dependent on protein availability (diet) and hepatic function
renal handling of urea
GF then reabsorption of up to 50% for the filter load of urea in the proximal tubule
urea crosses memb by passive diffusion (along with water; dependent on reabsorption of water)
normal BUN
5-20 mg/dL
normal BUN:SCr ratio
10-15.1
As ratio gets higher (like more than 20:1), it is usually a early sign of renal failure
normal SCr
0.5- 1.5 mg/dL
how is creatinine mainly eliminated?
primarily by glomerular filtration (so as GFR declines, SCr conc will increase)
method to determine creatinine concentration
Jaffe reaction= rxn of creatinine with alkaline picrate (but also reacts with noncreatinine chromogens in the serum so it might be falsely elevated)
normal CrCl
Men= 90-139 mL/min Women= 80-125 mL/min
CrCl calculation
CrCl= (urine Cr conc x urine vol) / (serum Cr conc x duration of urine collection)
what substances also react with the procedure for CrCl?
Age, weight, gender Diet Diurnal variation Drugs (cimetidine, trimethoprim, probenicid) Exercise
what is SCr dependent on?
muscle mass (more mass- more SCr)
exercise (increases SCr)
elderly pts
diurnal variation (peak is in the morning)
dietary intake of creatinine (cooking meats converts creatine to creatinine)
cystatin C
synthesize in all nucleated cells at a constant rate
cleared from the body by glomerular filtration
*provide an ideal marker of GFR since the conc is independent of age and gender but it is costly to assay
urinalysis
Can give both quantitative and qualitative analysis of renal function
pH range
4.5-7.8
high pH may suggest what?
urea-splitting bacteria or renal tubular necrosis
specific gravity range
1.003-1.030
specific gravity
weight of an equal vol of urine and water (dependent on water intake and urine conc ability)
can be offset by large particles (so osmolality is more accurate)
glucose in urine
once serum glucose exceeds 160-200 mg/dL, (max threshold for glucose reabsorption) glucose will be excreted in the urine
what is excreted in the urine of pts with diabetic ketoacidosis?
acetoacetate and acetone
what is suggestive of a UTI in the urine?
nitrite and leukocyte esterase along with heme or protein or albumin
protein excretion range in heatlhy adults
30-150 mg/day (which approx 30 mg/day is albumin since albumin is not filtered due to size and negative charge)
MDRD (modified diet in renal disease) study equation
(use 4 variable equation to estimate GFR)
GFR= 175 x SCr^ -1.154 x age^ -0.203 x 1.212 (black) x 0.742 (female)
more popular in clinic but tends to underestimate measured GFR when >60 mL/min
CKD-EPI
more accurate than the MDRD study equation, esp at estimated GFR >60 mL/min!
