renal - lecture 2

Question 1

compare plasma and filtrate

Answer 1

plasma = water and low molecular weight substances freely moves across filtration barrier to filtrate

Question 2

what does plasma have that filtrate does not

Answer 2

cells =rbcs, wbcs = hematuria
proteins like albumins, globulins - if see albumin in pee = proteinuria= bad
protein bound substances = 1/2 calcium ion (since half bound to protein), fatty acids

Question 3

name and describe forces involved in filtration

Answer 3

major force is pressure

pbs from bowmans space
= glomerular cap bp
no oncotic since no proteins
pcg and pigc from capillary
= fluid pressure in bowmans space, osmotic force due to protein in plasma = oncotic pressure
net = pgc-pbs-pigc = 16

Question 4

what is gfr

Answer 4

the volume of fluid filtered from the glomeruli into Bowman’s space per unit time

Question 5

what is gfr regulated by

Answer 5

net filtration pressure
membrane permeability
surface area available for filtration
last 2 = usually affected during disease, not usually regulated

Question 6

what is normal gfr

Answer 6

70kg person = 180l/day (125ml/min)
plasma vol of person = 3.5l
180/3.5 = 51 = plasma filtered 51 times a day at glomeruli

Question 7

describe regulation of gfr - decreased gfr

Answer 7

reduce net filtration pressure by constricting flow in efferent
and dilate efferent arteriole = outflow

Question 8

describe regulation of gfr - increased gfr

Answer 8

constrict efferent arteriole = pressure increased
and dilate afferent arteriole = more blood flow

Question 9

what is filtered load

Answer 9

total amount of any freely filtered substance = for individual substance
filtered load = gfr x plasma concentration of substance

Question 10

give ex of filtered load

Answer 10

of glucose
180l/day x 1g/l = 180g/day

Question 11

compare filtered load and amount excreted in urine

Answer 11

filtered load > amount excreted in urine = net reabsorption
filtered load < amount excreted in urine = net secretion

Question 12

describe reabsorption - 2 ways

Answer 12

paracellular = through tight junctions connecting epithelial cells cuboidal
transcellular = through cells
basolateral = face blood side
luminal membrane = face tubular lumen

Question 13

describe tubular reabsorption

Answer 13

water = 99% reabs
sodium = 99.5%
Glucose = 100%
urea = 44% (waste product )
net = 86.1, balance of secretion and reabsorption
k+ secreted too

Question 14

describe 4 important facts about tubular resabsorption

Answer 14

filtered loads are enormous = generally greater than amounts of substance in body
reasb of waste products generally incomplete = urea
reasb of most useful plasma components is relatively complete = water, inorganic ions, organic nutrients
reabs of some substance not regulated = glucose, aas while others = highly regulated = water, inorganic ions

Question 15

name 2 mechanisms for reabsorption

Answer 15

diffusion and mediated transport

Question 16

describe diffusion - reabsorption

Answer 16

often across the tight junctions connecting the tubular epithelial cells = paracellular

Question 17

describe diffusion example - reabsorption

Answer 17

urea reabs in proximal tubule
urea freely filtered at glomerulus
in proximal tubule = water reabsorption occurs
urea concentration in tubular fluid becomes higehr
urea diffused into interstitial fluid and eventually peritubular caps

Question 18

describe mediated transport - gen - reabsorption

Answer 18

occurs across tubular cells = transcellular epithelial transport
requires participation of transport proteins in plasma membrane of tubular cells = usually coupled to the reabs of sodium

Question 19

describe mediated transport - specifics - reabsorption

Answer 19

nak atpase = pumps out sodium and in potassium = intracellular sodium goes down
Glucose and aas = transport proteins eventually has to get back to cap
sodium cotransporter - symporter same direction, aa and sodium too

Question 20

what is tm

Answer 20

when membrane transport proteins become saturated= tubule cannot reabsorb substance any more = limit = transport max = tm

Question 21

describe tm for ppl with diabetes mellitus

Answer 21

Uncontrolled diabetes mellitus = plasma concentration of glucose can be v high and filtered load of glucose exceeds capacity of the tubules to reasb glucose = tm exceeded
= glucose appears in urine glucosuria= dipstick test = first sign of diabetes mellitus

Question 22

describe tubular secretion and how its mediated

Answer 22

moves substances from peritubular capillaries into tubular lumen = opp of reabs
mediated by diffusion and transcellular mediated transport

Question 23

describe secretion - tubular secretion

Answer 23

most important substances secreted by tubules = hydrogen and potassium ions
tubular secretion usually coupled to reabs of sodium

Question 24

describe division of labor in tubules - gen

Answer 24

in order to excrete waste products adequately = gfr must be very large
filtered vol of water and filtered loads of all nonwaste plasma solutes are also v large

Question 25

describe division of labor in tubules - proximal tubule

Answer 25

reabsorbs majority of this filtered water and solutes
major site of secretion for various solutes EXCEPT potassium

Question 26

describe division of labor in tubules - henles loop

Answer 26

reabsorbs large quantities of major ions, not much water
mainly electrolytes

Question 27

describe division of labor in tubules - dct/cd

Answer 27

volume of water and masses of solutes reaching here are small
= fine tuning here
determines final amounts excreted in urine by adjusting rates of reabs and in some cases secretions
most homeostasis controls here

Question 28

what is clearance

Answer 28

volume of plasma from which that substance is completely removed - cleared by kidneys per unit of time

Question 29

what is clearance formula

Answer 29

clearance of s (Cs) = mass of 2 excreted per unit time/plasma concentration of s (ps)

mass of 2 excreted per unit time = urine concentration of s US x urine volume per time V

Cs = UsV/Ps

Question 30

describe inulin clearance

Answer 30

polysaccharide that is given intravenously
freely filtered at glomerulus but not reabs, secreted or metabolized by tubule
so clearance of inulin - Cin = to vol of plasma originally filtered = GFR
so Cin = GFR - most accurate marker of gfr

Question 31

describe how to calculate gfr from inulin

Answer 31

urine vol = 2.4l/day
inulin conc in urine = 300mg/l
amount of inulin excreted in urine = 2.4l/day x 300mg/l = 720mg/day
cin = 720mg/day divided by 4mg/l = 180l/day
* 4mg/l = concentration of inulin in plasma
gfr = cin = 180l/day
not convenient

Question 32

describe creatinine clearance

Answer 32

creatinine = waste product produced by muscle, endogenous
filtered freely at glomerulus not reabs
secreted at tubule but amount v small
not metabolized by tubule
thus, creatinine clearance used as clinical marker for gfr

Question 33

describe creatinine clearance calculation

Answer 33

v=urine vol, ucr = urine conc of creatinine, pcr = plasma conc of creatinine
creatinine clearance = UcrV/Pcr ~ equal to gfr

ex =
urine vol = 2l per day
ucr = 9.6mmol/l
pcr = 0.3mmol/l
= 9.6 x 2/ 03 = 64l per day = person lost 2/3 gfr - normal = 180

Question 34

compare clearance vs gfr

Answer 34

Clearance = for substance
gfr = uniqe to person

clearance of substance > gfr = secreted at tubule
clearance of substance < gfr = reabsorbed at tubule

Question 35

compare clearance vs gfr for specific substances

Answer 35

Clearance > gfr = secreted = like PAH, marker of renal plasma flow, clearance equal to renal plasma flow
Clearance < gfr = reabsorption = water, sodium, glucose