5. Renal Function Flashcards by Samantha Boyer

nephrons in kidney

1-1.5 million

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—- minor calyces join to form —- major calyces, which drain into the…

12
2-3
renal pelvis

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medullary rays

striations in renal pyramids which connect the cortex with the medulla

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urethra length

males 24 cm
females 4 cm

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capillary lobes in glomerulus

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3 layers of glomerular filtration barrier

capillary endothelials, basement membrane, visceral epithelium of Bowman’s capsule

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shield of negativity function

prevents passage of + molecules
including albumin

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——% of filtrate is reabsorbed in the PCT

60-80%

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—% Na+ is reabsorbed in the PCT

67%

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pars recta

thick descending limb of loop of Henle

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vasa recta

capillaries adjacent to loops of Henle
major exchange of salt and water
maintain osmotic gradient

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renal artery receives –% of blood from heart

25%

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glomerular filtration rate

volume of plasma that is filtered by the glomerulus in a specified time

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juxtaglomerular apparatus

autoregulatory mechanism that maintains glomerular BP at a relatively constant rate regardless of fluctuation of systemic BP

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RAAS responds to…

↓ BP
↓ Na+ concentration

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renin

secreted by juxtaglomerular cells in response to ↓ BP and ↓ Na+

forms angiotensin

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5 effects of angiotensin II

afferent vasodilation
efferent constriction
stimulates reabsorption of Na+ and water in PCT
↑ K+ excretion
triggers aldosterone release

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Na+ retaining hormone

aldosterone

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3 functions of ADH

decreased urine production
decreased sweating
increased BP

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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

1. solute-free H2O (cleared) 2. 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

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