Exam 3 Flashcards
What solutes are used to monitor renal function
urea and creatinine
What measurements are used to asses quantity of solutes in urine
SG and osmo
What are the 3 most abundant solutes in urine
urea
chloride
sodium
What are the 3 least abundant solutes in urine
Uric acid
glucose
albumin
What is osmolality
the number of particles in a solution
Urea ____ dissociate in solution
NaCl ___ dissociates in solution
Which one has the highest osmolality
urea does not
NaCl does
NaCl has twice the osmo than urea
IF the osmo of the initial filtrate = the osmo of the plasma
isosmotic
Ultrafiltrate in Bowman;s space has ___ solute composition as plasma, but lacks ___
the same
lacks albumin
What is the osmolality of the ultrafiltrate in Bowman’s space and plasma
300 mOsm
What determines the final osmo of urine
the distal tubules and collecting ducts
If ADH is present, does osmo increase or decrease as water absorbed in the collecting ducts
increases
What is the max osmo possible
What is the normal osmo
max- 1400
normal-275-900
Where can urine be hypertonic
medullary interstitium
What produces hypertonic urine
posterior pituitary releases ADH
what is the normal urine to serum osmo ratio
1-3
Urine osmo should be ___x the serum osmo
1 to 3 times
What is polydipsia
intense thirst, brought on by diabetes
ADH makes you pee ___ water, making urine ___ concentrated
less water
more concentrated
What is specific gravity
ratio of mass of solutes to pure water
What is the normal SG range
1.002 to 1.035
How do large molecules affect the SG value
dramatically increases SG compared to small solutes
What are some large molecules that can be present in urine
Glucose
What can cause an extremely high SG
> 1.050
X ray dye or mannitol
DOES NOT AFFECT OSMO
What is the difference between osmo and SG
osmo-# of solutes
SG- mass of solutes
both measurements of concentration of urine
What is the normal daily urine excretion
500-1800
How much urine do the kidneys secrete when a person is dehydrated? and excessively hydrated?
dehydrated- small volume
excessively hydrated-large volume
What are the 2 main causes of polyuria
water diuresis- low osmo >200, inadequate ADH secretion or inactive action of ADH
solute diuresis- > 300 , usually imbalance of glucose, urea, sodium
what is oliguria? and anuria
oliguria- decreased urine- <400
anuria- no urine excretion
Which is preferred? Osmo or Sg and why
Osmo- because its more accurate
except for HMW solutes
How is tubular concentration affected in chronic renal disease? What happens to SG and osmo?
causes inability to rebsorb and secrete solutes from ultrafiltrate
SG and osmo- same as initial ultrafiltrate in Bowman’s space
causes polyuria and nocturia
What is a fluid deprivation test and what is its purpose
Deprive patient of fluids from 6pm to 8am
ADH administered at the end
To find causes of water diuresis, could be defective ADH or lack of a response to ADH
Match neurogenic or nephrogenic
-lack of ADH response
-defective ADH
neurogenic- defective ADH
nephrogenic- lack of ADH response
What does a positive response and a negative response to fluid deprivation test
positive- urine osmo high- this means the kidneys responded to the ADH, therefore the patient must not be producing enough ADH-neurogenic problem
negative- urine osmo low- this means the renal receptors for ADH must not be working, because there is no response when ADH is present- nephrogenic problem
What is osmolar clearance
What is free clearance
osmolar clearance- ratio of urine osmo to serum x urine volume
Free water clearance- additional water that exceeds bodily needs and is eliminated in the urine
When the total urine equal the osmolar clearance volume
urine is _____ with plasma
Ch20 is ___
urine osmo = serum osmo
isosmotic
CH2O is zero
When urine is dilute because of water diuresis
urine is _____
The CH2O is ____
urine is hypo-osmotic or hypotonic
Uosmo
When urine is concentrated due to dehydration
urine is ___
CH2O ___
urine is hyperosmotic
CH2O is negative
How does dehydration affect
Uosm
Sosm
V
Cosm
CH2O
Uosm- increases
Sosm- increases
V-decreases
Cosm- decreases
CH2O- decreases
Practice the formula for Osmolar clearance
Cosm = (Uosm/Sosm) x V
What units should creatinine clearance be in what other formulas have the same unit
mL per minute not hr
RBF
Practice the formula for renal clearance
C= U x V/ P
U=urine
P=plasma
What is GFR in general?
What is the measured GFR? and estimated?
glomerular filtration rate- the rate of plasma cleared by the glomeruli
measured- using clearance test
estimated- using equation or biomarkers
What is the normal reference range for GFR
What do the abnormal results mean
> 60 normal
<60 kidney disease
< 15 kidney failure
What is inulin
not absorbed by GI tract, administered before and throughout the inulin clearance test
passes through glomerular filtration and is NOT reabsorbed
ideal substance for determining GFR, not practical for routine/ periodic GFR
What is the most frequently used test for routine assessment of GFR
creatinine clearance
How can more accurate creatinine testing be obtained
using 24 hr urine collection
What is creatinine
a biproduct of muscle metabolism
Is creatinine varied or constant in its production
should be steady, constant plasma and urine excretion rate
What influences creatinine production
muscle mass, can vary depending on age, gender and physical activity
What is the average persons body surface area, why is it used in calculations for creatinine clearance
1.73m^2
accounts for the differences in muscle mass in individuals
Practice the creatinine clearance calculation
C= ((U x V)/ P ) x (1.73/SA)
P= plasma
U=urine
SA= patient surface area
What can normal creatinine clearance be?
between 30 and 130
What special consideration must be kept in mind for creatinine clearance testing
-24 hr urine- to account for diurnal variation in GFR
-must be stored correctly to avoid bacteria proliferation which can breakdown creatinine
-must have the correct urine volume
When do we use estimated GFR
when serum creatinine test is done on patients older than 18
What is the reference range for creatinine clearance
88-137
What other markers can we use to determine GFR other than creatinine, name the advantages and disadvantages, are the absorbed?
Cystatin C- the same in every age group, muscle mass and gender, does not return to blood circulation, expensive
Beta 2 microglobulin- is reabsorbed completely, concentration is constant
As blood cystatin C levels increase, GFR ____
decreases
As tubular capacity to reabsorbe decreases, B2 microglobulin ____
increases in concentration in the urine
what is the purpose of screening for microalbuminuria
to monitor patients with diabetes, can detect early nephropathy