Quiz 1

Question 1

ineffective osmoles

Answer 1

reflection coefficient at equilibrium is t generate an osmotic effect.

Question 2

osmolality calculation; osmolar gap

Answer 2

osmolality = 2[Na] + [glucose]/18 + [BUN]/2.8
osmolar gap = measured - calculated; alters you to the presence of a toxin in the blood at high enough concentration to affect measured osmolality

Question 3

Fluid compartment rules

Answer 3

TBW=60% of BW, ICF=40% of BW, ECF=20%. ECFV is 75% ISFV and 25% PV.

Question 4

forces driving fluid movement between plasma and ISF

Answer 4

hydrostatic pressure: plasma–>ISF

oncotic pressure due to plasma proteins: ISF–>plasma

Question 5

filtration rate

Answer 5

Kf= [(Pc-Pi) - σ(πc - πi)]

Question 6

ultrafiltration rate/day

Answer 6

180L/day, necessitating 20% of CO. Filtration is passive but reabsorption isnt.

Question 7

O2 consumption by kidneys

Answer 7

determined by GFR, which varies based on RPF. A-V O2 difference is constant while O2 consumption, GFR and RBF increase

Question 8

starling equation for GFR

Answer 8

GFR=Kf[(Pgc-Pbs)]-πgc]
different from other caps because of Kf
driven by Pgc

Question 9

filtration fraction

Answer 9

GFR/RPF, ~20%, limited by πgc (increases as protein free filtrate leaves the glomerulus)

Question 10

constriction of afferent arteriole

Answer 10

Pgc↓ so GFR ↓, RPF↓

Question 11

constriction of efferent arteriole

Answer 11

Pgc↑ so GFR↑, RPF↓

Question 12

renal clearance

Answer 12

virtual volume of plasma that would be completely cleared of a substance per unit time = Us x V’ /Pas (concentration in arterial plasma)

Question 13

clearance of PAH

Answer 13

measures RPF, since PAH is both filtered and secreted and doesnt appear in the vein
RPF = Upah x V / Pa pah

Question 14

clearance of inulin and creatinine

Answer 14

measures GFR, since its freely filtered but neither secreted nor reabsorbed from tubules. Creatinine is alternative, advantage is its endogenously produced but disadvantage is that its secreted in the PT, so that at low GFR, tend to overestimate

Question 15

autoregulation of RBF and GFR

Answer 15

1) myogenic mechanism: ↑BP→intrinsic smooth muscle contraction
2) tubuloglomerular feedback: when RBF and GFR are high, MD senses higher NaCl load AND flow and alters afferent arteriole resistance, which bring RBF and GFR down

Question 16

vasoactive effects on Na reabsorption in tubules

Answer 16

vasodilators are naturietic (increase Na discharge)

vasoconstrictors are antinaturietic (decrease Na discharge)

Question 17

major regulators of renin release

Answer 17

afferent arteriolar pressure: ↑pressure - ↓renin
sympathetic tone: ↑activity - ↑renin
NaCl load @MD: ↑load - ↓renin
pressor hormone: ↑levels - ↓renin

Question 18

effects of AII on renal hemodynamics

Answer 18

↑↑↑efferent tone
↓renin secretion
preserves GFR while counteracting reduced perfusion pressure

Question 19

NSAIDS effect

Answer 19

when have congestive heart failure, can decrease GFR dramatically because prostaglandins counter vasoconstriction. When their synthesis is inhibited, high vasoconstriction will make GFR drop

Question 20

characteristics of solute transport along nephron

Answer 20

transport capacity: decreases as →
driving force: increases as →
leakiness: decreases as →
energy efficiency: decreases as →

Question 21

PT main functions

Answer 21

reabsorption of 2/3rds of Na and H2O, all nutrients, 80% of bicarb and phosphate, and secretion of xenobiotics.
Transporters: Na/nutrient coupled reabsorption, Na/H+ exchanger to aid in bicarb reabsorpt.
solvent drag from leaky TJs

Question 22

late PT transport

Answer 22

[Cl-] increases, diffuses through TJ, lumen + voltage drives Na+ out of lumen paracellularly

Question 23

regulation of Na/H2O trasnport in the PT

Answer 23

GT balance: PT always reabsorbs 2/3rds of filtered load despite changes in GFR. Main reason: high GFR creates high π and low hydrostatic P in peritubular capillaries, increasing reabsorption

Question 24

functions of loop of henle

Answer 24

reabsorb 25% of filtered Na (only in ascending limb) but only 15% of filtered H2O (only in descending limb)
direct dilution of urine
indirect, permissive concentration of urine

Question 25

TAL transport

Answer 25

Na+/2CL-/2K+ cotransporter; recycling of K+ creates a lumen + voltage that drives paracellular Na, Ca++, Mg++, K+ and NH4+ transport.
rate of paracellular = transcellular

Question 26

regulation of LH transport

Answer 26

loop diuretics: inhibit Na/K/Cl transporter, used to treat edema assoc. w/ heart failure and hepatic cirrhosis
rate of Na reabsorption increases w/ Na delivery
Ca++ receptors on basolateral TAL cells sense high [Ca] and inhibit K+ channels letting K+ back into lumen.
also regulated by NO and prostaglandins

Question 27

MD

Answer 27

transport via Na/K/Cl, contributes to renin secretion

Question 28

main functions of DT

Answer 28

reabsorbs 5% of filtered NaCl via Na/Cl cotransporter, NO H2O, contributes to dilution of urine. Na transport is strictly transcellular

Question 29

main functions of the CD

Answer 29

major role in regulation of Na balance (ECFV); 4% of Na reabsorption (strictly transcellular) and ~15% (0-20%) of H2O reabsorption. Regulation of H2O balance (exclusive site of regulated H2O transport)

Question 30

ion transport in the CD

Answer 30

ENaC: apical Na channel driven by low intracellular [Na] and negative potential inside cell - can render tubular fluid nearly Na-free. K secretion is coupled to Na reabsorption; K sparing diuretics block ENaC and therefore conserve K.
aldosterone regulates Na
ADH regulates H2O

Question 31

main stimulus for ADH secretion and thirst

Answer 31

increase in effective plasma osmolality

Question 32

Osmotic control via ADH and thirst

Answer 32

ADH onset at approx plasma osmolality of 282 mOsm/kg H2O and plasma [Na] of approx 138 meq/L
Thirst onset at approx plasma osmolality of 290 mOsm/kgH2O and plasma [Na] of 145

Question 33

volumetric control of ADH secretion

Answer 33

decrease in blood volume or pressure of >15%

Question 34

volumetric control of H2O balance

Answer 34

high [Na]→ADH and thirst osmoreceptors→neurohypophysis secretion of ADH and thirst center stimulated, ADH acts on kidneys
renin secreted from kidneys→AII→increases thirst
ANP from heart inhibits ADH osmoreceptors

Question 35

protection against overhydration

Answer 35

cold receptors and GI metering

Question 36

countercurrent exchange

Answer 36

medullary vasa recta get teeny flow and sluggish movement to preserve Na gradient

Question 37

countercurrent multiplier

Answer 37

hairpin structure of LH exploited to increase the osmolality of the interstitium and create a large axial Na gradient

Question 38

effects of ADH

Answer 38

increased H2O permeability of all CD

increased urea permeability of medullary CD

Question 39

renal handling of urea

Answer 39

50% is reabsorbed in PT via paracellular diffusion and solvent drag. High urea permeability in LH where up to 70% (but as little as 10%) moves back into lumen, then medullary CD has high urea permeability during antidiuresis→reabsorbs 90%, which creates large urea gradient and effectively uncouples urea excretion from needing H2O also.

Question 40

diabetes insipidus

Answer 40

central: inadequate release of ADH
nephrogenic: kidney is resistant to ADH

Question 41

SIADH

Answer 41

ectopic ADH secretion that is not suppressed by low plasma osmolality

Question 42

free water clearance

Answer 42

rate at which water needs to be added to or subtracted from urine to render it isoosmotic with plasma. Excess h2o secretion=positive, excess solute=negative