Body Fluids and Clearance

Question 1

body water fraction in males and females

Answer 1

60 in men, 50 in women

Question 2

water distribution across comparments

Answer 2

2/3 intracellular

1/3 ECF- 1/4 of which is plasma, 3/4 is interstitial

Question 3

content difference in plasma and interstitium

Answer 3

much higher protein in plasma, but ions equillibriate

Question 4

define osmolality

Answer 4

mOsm/kg, number of particles in kg of fluid

Question 5

calculate total osmolality

Answer 5

osm= 2Na+ glucose/18 + BUN/2/8 + EtOH/3.7

Question 6

what is tonicity, how to calculate

Answer 6

tonicity=effective osmolality, component of osmolality that contributes to osmotic force (must not permeate thru barrier)

2Na + glucose/18

Question 7

usual osmolalty of ICF/ECF

Answer 7

usually b/w 275-295, ECF can change transiently in response to changes in osmolality/tonicity from Na or H2O fluctuations- this affects ICF

Question 8

what is net excretion

Answer 8

filtration + secretion - reabsorption

Question 9

normal GFR

Answer 9

120 mL/min adult males, 95 in females

Question 10

filtered load

Answer 10

GFR x Py (plasma concentration)

Question 11

excreted load

Answer 11

V (urine flow) x Uy (urine concentration)

Question 12

reabsorption

Answer 12

filtered load- excreted load

Question 13

secretion

Answer 13

excreted load- filtered load

Question 14

clearance of y

Answer 14

VxUy/Py= excreted load/plasma concentration

requires steady state of plasma concentration

Question 15

when does clearance = GFR

Answer 15

when everything filtered is excreted, excreted load =filtered load, no secretion or reabsorption

GFR= UV/P

Question 16

why is creatinine good for GFR measurement

Answer 16

relatively constant production, disposed by filtration, non invasive (unlike inulin)

Question 17

describe changes in plasma and urine creatinine following acute change in GFR

Answer 17

early- GFR falls as does filtered and excreted load of Cr, plasma Cr is the same

later- GFR still low, but plasma Cr has increased due to lower excretion (constant production), the proportional rise in plasma Cr brings filtered rate back to where it was

new steady state

Question 18

para amino hippuric acid approximates which value

Answer 18

renal plasma flow- all that enters kidney is excreted via filtration and secretion (90%)

Question 19

calculate RPF and RBF for PAH

Answer 19

RPF= (UV/P)/0.9 (extraction ratio)

RBF= RPF/1-Hct

Question 20

filtration fraction

Answer 20

fraction of plasma that is filtered:

FF= GFR/RPF

Question 21

3 layers to filtration barrier

Answer 21

from lumen of capillary: endothelial cell, basement membrane, podocytes w/ foot processes

Question 22

what determines which things are filtered

Answer 22

charge and size: less than 40 A are filtered, 20 A are freely filtered

negative things less filtered (negative basement membrane)

ions freely filtered

Question 23

how is glomerular hydrodynamics different from other capillaries

Answer 23

high hydrostatic pressure, more than COP throughout (despite increasing COP as plasma becomes more concentrated)

arterioles on both sides, no venous end

Question 24

how is GFR maintained despite range of blood pressures- 3 main ways

Answer 24

autoregulation- arterioles resist stretching to maintain steady blood flow, RAAS system activated by low pressure in afferent and low Cl delivery to macula densa and sympathetic innervation

increased AII and NE constricts efferent to raise GFR, also stimulates prostaglandins that work in opposite direction

macula densa can dilate the afferent arteriole during low Cl delivery to raise GFR, tubuloglomerular feedback

Question 25

describe the renal response to hypovolemia/hypervolemia

Answer 25

RAAS activation, AII causes efferent constriction, increased FF, COP in capillary increases, more PCT reabsorption

opposite of all this occurs in hyper

Question 26

urinary obstruction effect on GFR

Answer 26

increased hydrostatic pressure in bowmans space, opposes filtration so GFR goes down

Question 27

NSAIDs impact on GFR

Answer 27

block prostaglandin synthesis (normally afferent vasodilation) which oppose AII and NE effects, causes more afferent vasoconstriction and lower GFR

Question 28

meaning of : CxGFR

Answer 28

clearance greater than GFR= net secretion

less than = net reabsorption

equals GFR= no net secretion or reabsorption

Question 29

key factors for concentrated urine

Answer 29

medullary gradient: NaCl reabsorption w/o water in ascending limb, slow flow

ADH in plasma, response in CD

nephron lenght and enough solute intake

Question 30

which segment has most water uptake

Answer 30

CCD

Question 31

why impaired urinary concentration in sickle cell

Answer 31

loss of vasa recta, effectively shortens loop of nephron and leads to polyuria and nocturnal enuresis in young pts

Question 32

fractional excretion equation

Answer 32

amount excreted/filtered load

(Ux/Px)/ (Ucr/Pcr) x 100

Question 33

use of fractional excretion

Answer 33

assess renal handling of specific solute like Na

Question 34

differentiate AQP1, 2, and 3

Answer 34

1: PCT, descending limb, not ADH regulated,apical and basolateral
2: DCT, CCD and MCD, ADH regulated on apical memrane
3: DCT, CCD and MCD on basolateral, constitutive

Question 35

why do small increases in CO2 cause major pH drops

Answer 35

change in H+ has bigger effect than the increase in bicarb, way less H+ in circulation