5. Renal Function Flashcards
nephrons in kidney
1-1.5 million
—- minor calyces join to form —- major calyces, which drain into the…
12
2-3
renal pelvis
medullary rays
striations in renal pyramids which connect the cortex with the medulla
urethra length
males 24 cm
females 4 cm
capillary lobes in glomerulus
8
3 layers of glomerular filtration barrier
capillary endothelials, basement membrane, visceral epithelium of Bowman’s capsule
shield of negativity function
prevents passage of + molecules
including albumin
——% of filtrate is reabsorbed in the PCT
60-80%
—% Na+ is reabsorbed in the PCT
67%
pars recta
thick descending limb of loop of Henle
vasa recta
capillaries adjacent to loops of Henle
major exchange of salt and water
maintain osmotic gradient
renal artery receives –% of blood from heart
25%
glomerular filtration rate
volume of plasma that is filtered by the glomerulus in a specified time
juxtaglomerular apparatus
autoregulatory mechanism that maintains glomerular BP at a relatively constant rate regardless of fluctuation of systemic BP
RAAS responds to…
↓ BP
↓ Na+ concentration
renin
secreted by juxtaglomerular cells in response to ↓ BP and ↓ Na+
forms angiotensin
5 effects of angiotensin II
afferent vasodilation
efferent constriction
stimulates reabsorption of Na+ and water in PCT
↑ K+ excretion
triggers aldosterone release
Na+ retaining hormone
aldosterone
3 functions of ADH
decreased urine production
decreased sweating
increased BP
defect in NH3 production
renal tubular acidosis
inability to produce acid urine
tests used to detect an acid-base imbalance
- pH
- titratable acidity
- urinary ammonia
important characteristics of substance for clearance test (5)
neither be reabsorbed nor secreted; stability over time; plasma consistency; availability to the body; ability to analyze substance
substances used in clearance tests
creatinine
cystatin C
B2-microglobulin
radioisotopes
inulin (gold standard but invasive)
eGFR used with —— clearance test
creatinine
clearance test reported in…
mL/min
creatinine clearance AKA ——
GFR
clearance calculation and variable definitions
C = UV/P = mL/min
C = GFR
U = urine concentration in mg/dL
V = volume urine in mL/min
P = plasma concentration in mg/dL
24 hr = —- min
1440
concentration =
(units?)
Conc = UV = g/24 hours
normal creatinine reference range
0.5-1.5 mg/dL
corrected creatinine clearance calculation
Corrected CrCl = (UV/P)(1.73/A)
A = BSA score from nomogram
1.73 = average body surface area in m^2
traditional vs current eGFR systems
traditional: MDRD-IDMS; considered sex and ethnicity
current: CKD-EPI 2021; no longer considers ethnicity
clearance test
produced by all nucleated cells at constant rate
serum levels directly reflect GFR
for pediatrics, diabetics, elderly, critically ill
cystatin C
clearance test
dissociates from human leukocyte antigens at constant rate
measured by immunoassay
unreliable in those with immune disorders/malignancies
B2-microglobulin
clearance test that does not require urine collection and can measure viability of transplanted kidney
radionucleotide
125I iothalamate
normal osmolality after fluid deprivation
> 800 mOsm/kg
3:1 urine:serum ratio
is osmolality is abnormal after fluid deprivation…
testing continues for 2 more hours
if it’s still abnormal, move on to ADH challenge
osmolality
number of osmoles per kilogram of solvent
isosmotic
osmolality of initial filtrate = that of plasma
1.010 SG
normal osmolality ranges for urine and serum
urine: 50-1400 mOsm/kg
serum: 275-300 mOsm/kg
3 substances that can cause false results in osmolality readings
lipemic serum
lactic acid
ethanol
free water clearance
volume of water cleared by the kidneys per minute in excess of that necessary to remove solutes
ADH levels vs free water clearance
low ADH, (+) CH2O
high ADH, (-) CH2O
osmolar clearance calculation
Cosm = UosmV/Posm
free water clearance calculation
CH2O = V - (UosmV/Posm)
2 parts of water in free water clearance
- solute-free H2O (cleared)
- H2O with solute
reference range for normal renal plasma flow
600-700 mL/min
measures renal plasma flow
PAH
normal person excretes — mEq/day of acid
70
forms of acid in the urine
H+
H2PO4-
NH4+
alkaline tides
shortly after arising
postprandially 2pm
postprandially 8pm
lowest urine pH time
night
evaluates ability of tubules to secrete ammonium and hydrogen
oral ammonium chloride test
acid load of oral ammonium chloride
speciments collected at — hour intervals
—-, —-, and —– are measured
ammonium concentration =
2 hour
pH, titratable acidity, and urinary ammonia
ammonium concentration = titratable acidity - total acidity
normal BUN
7-20 mg/dL
