Quantification of Renal Function

Question 1

what do macula densa cells do?

Answer 1

sense changes in the volume delivery to the DT (senses the contents of the glomerular fluid)

Question 2

when does erythropoietin get secreted?

Answer 2

in response to oxygen tension in the blood

Question 3

metabolic function of the kidney

Answer 3

1. activation of Vit D3
2. gluconeogenesis
3. metabolism of insulin, steroids, and xenobiotics (mostly in cortex)

Question 4

secretion ___ impacts what ends up being in final product of urine

Answer 4

positively (positively impacts excretion)

Move in the direction of peritubular capillary blood to the tubular fluid

Question 5

absorption ___ impacts what ends up being in final product of urine

Answer 5

negatively (negatively impact excretion)

tubular fluid → capillary blood

Question 6

glomerular filtration

Answer 6

passive diffusion of water and SMALL molecules across glomerular capillary and into Bowman’s capsule and PT

Question 7

What size proteins are too large to be filtered across glomerular capillary?

Answer 7

> 60 kDa

Large proteins get impeded and do not cross the glomerular capillary

Question 8

secretion

Answer 8

active transport
occurs mostly in proximal tubule (anionic and cationic transporter syst are present and involved in the elimination of many drugs

Question 9

anionic drugs that are secreted

Answer 9

probenicid, penicillin

Question 10

cationic drugs that are secreted

Answer 10

creatinine, cimetidine, procainamide

Question 11

which glycoproteins are involved in the elimination of cytotoxic drugs?

Answer 11

P-gp and multidrug resistance protein

Question 12

where does drug reabsorption occur in the kidney?

Answer 12

along the distal tubule and collecting tubules

Question 13

Intact Nephron Hypothesis

Answer 13

renal disease is the result of reduced number of appropriately functioning nephrons (remaining nephrons compensate for the diseased ones)

Question 14

single nephron GFR (SNGFR) in renal disease

Answer 14

increases in the remaining nephrons and whole kidney GFR represents the sum of SNGFR of the remaining functional nephrons

Question 15

s/sx of renal dysfunction

Answer 15

HTN, edema, electrolyte imbalance, anemia, increased urine output, metabolic acidosis (mild), bone demineralization, hyperkalemia, mental confusion, nausea, vomiting (from accumulated urea)

Question 16

what are the 2 most important lab values for renal dysfunction?

Answer 16

BUN and SCr

Question 17

how is urea made in the kidney?

Answer 17

AA → ammonia → urea

(prod of urea is dependent on protein availability (diet) and hepatic function

Question 18

renal handling of urea

Answer 18

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)

Question 19

normal BUN

Answer 19

5-20 mg/dL

Question 20

normal BUN:SCr ratio

Answer 20

10-15.1

As ratio gets higher (like more than 20:1), it is usually a early sign of renal failure

Question 21

normal SCr

Answer 21

0.5- 1.5 mg/dL

Question 22

how is creatinine mainly eliminated?

Answer 22

primarily by glomerular filtration (so as GFR declines, SCr conc will increase)

Question 23

method to determine creatinine concentration

Answer 23

Jaffe reaction= rxn of creatinine with alkaline picrate (but also reacts with noncreatinine chromogens in the serum so it might be falsely elevated)

Question 24

normal CrCl

Answer 24

Men= 90-139 mL/min
Women= 80-125 mL/min

Question 25

CrCl calculation

Answer 25

CrCl= (urine Cr conc x urine vol) / (serum Cr conc x duration of urine collection)

Question 26

what substances also react with the procedure for CrCl?

Answer 26

Age, weight, gender
Diet
Diurnal variation
Drugs (cimetidine, trimethoprim, probenicid)
Exercise

Question 27

what is SCr dependent on?

Answer 27

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)

Question 28

cystatin C

Answer 28

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

Question 29

urinalysis

Answer 29

Can give both quantitative and qualitative analysis of renal function

Question 30

pH range

Answer 30

4.5-7.8

Question 31

high pH may suggest what?

Answer 31

urea-splitting bacteria or renal tubular necrosis

Question 32

specific gravity range

Answer 32

1.003-1.030

Question 33

specific gravity

Answer 33

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)

Question 34

glucose in urine

Answer 34

once serum glucose exceeds 160-200 mg/dL, (max threshold for glucose reabsorption) glucose will be excreted in the urine

Question 35

what is excreted in the urine of pts with diabetic ketoacidosis?

Answer 35

acetoacetate and acetone

Question 36

what is suggestive of a UTI in the urine?

Answer 36

nitrite and leukocyte esterase along with heme or protein or albumin

Question 37

protein excretion range in heatlhy adults

Answer 37

30-150 mg/day (which approx 30 mg/day is albumin since albumin is not filtered due to size and negative charge)

Question 38

MDRD (modified diet in renal disease) study equation

Answer 38

(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

Question 39

CKD-EPI

Answer 39

more accurate than the MDRD study equation, esp at estimated GFR >60 mL/min!