renal - lecture 2 Flashcards
compare plasma and filtrate
plasma = water and low molecular weight substances freely moves across filtration barrier to filtrate
what does plasma have that filtrate does not
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
name and describe forces involved in filtration
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
what is gfr
the volume of fluid filtered from the glomeruli into Bowman’s space per unit time
what is gfr regulated by
net filtration pressure
membrane permeability
surface area available for filtration
last 2 = usually affected during disease, not usually regulated
what is normal gfr
70kg person = 180l/day (125ml/min)
plasma vol of person = 3.5l
180/3.5 = 51 = plasma filtered 51 times a day at glomeruli
describe regulation of gfr - decreased gfr
reduce net filtration pressure by constricting flow in efferent
and dilate efferent arteriole = outflow
describe regulation of gfr - increased gfr
constrict efferent arteriole = pressure increased
and dilate afferent arteriole = more blood flow
what is filtered load
total amount of any freely filtered substance = for individual substance
filtered load = gfr x plasma concentration of substance
give ex of filtered load
of glucose
180l/day x 1g/l = 180g/day
compare filtered load and amount excreted in urine
filtered load > amount excreted in urine = net reabsorption
filtered load < amount excreted in urine = net secretion
describe reabsorption - 2 ways
paracellular = through tight junctions connecting epithelial cells cuboidal
transcellular = through cells
basolateral = face blood side
luminal membrane = face tubular lumen
describe tubular reabsorption
water = 99% reabs
sodium = 99.5%
Glucose = 100%
urea = 44% (waste product )
net = 86.1, balance of secretion and reabsorption
k+ secreted too
describe 4 important facts about tubular resabsorption
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
name 2 mechanisms for reabsorption
diffusion and mediated transport
describe diffusion - reabsorption
often across the tight junctions connecting the tubular epithelial cells = paracellular
describe diffusion example - reabsorption
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
describe mediated transport - gen - reabsorption
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
describe mediated transport - specifics - reabsorption
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
what is tm
when membrane transport proteins become saturated= tubule cannot reabsorb substance any more = limit = transport max = tm
describe tm for ppl with diabetes mellitus
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
describe tubular secretion and how its mediated
moves substances from peritubular capillaries into tubular lumen = opp of reabs
mediated by diffusion and transcellular mediated transport
describe secretion - tubular secretion
most important substances secreted by tubules = hydrogen and potassium ions
tubular secretion usually coupled to reabs of sodium
describe division of labor in tubules - gen
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
describe division of labor in tubules - proximal tubule
reabsorbs majority of this filtered water and solutes
major site of secretion for various solutes EXCEPT potassium
describe division of labor in tubules - henles loop
reabsorbs large quantities of major ions, not much water
mainly electrolytes
describe division of labor in tubules - dct/cd
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
what is clearance
volume of plasma from which that substance is completely removed - cleared by kidneys per unit of time
what is clearance formula
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
describe inulin clearance
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
describe how to calculate gfr from inulin
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
describe creatinine clearance
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
describe creatinine clearance calculation
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
compare clearance vs gfr
Clearance = for substance
gfr = uniqe to person
clearance of substance > gfr = secreted at tubule
clearance of substance < gfr = reabsorbed at tubule
compare clearance vs gfr for specific substances
Clearance > gfr = secreted = like PAH, marker of renal plasma flow, clearance equal to renal plasma flow
Clearance < gfr = reabsorption = water, sodium, glucose
