Lecture 32: Glomerular Filtration Flashcards
Objectives – List the components of the filtration barrier within the renal corpuscle – Describe the factors that determine net filtration pressure – Understand the mechanisms for the regulation of glomerular filtration rate
3 processes of nephrons and collecting ducts
glomerular filtration
tubular reabsorption
tubular secretion
glomerular filtration
part of blood plasma filtered into kidney golmerulus is a knot
blood flows through BP pushes plasma through fluid leaving pushed through filtering system
FILTRATION ONLY HAPPENS IN GLOMERULARIS
tubular re-absorption
water and useful substances reabsorbed into blood mostly water
tubular secretion
wastes are removed from blood and secreted into urine
excretion=
excretion= glomular filtration+secretion-re=absorption
rate of excretion
rate of filtartion + rate secretion - rate reabs
what enhances filterating capacity
thiness of membrane large SA of glomerular capps glomerular capp blood pressure high due to small size of efferent arteriole (exit smaller than input=more BP)
what does blood pressure produce?
glomerular filtrate
filtrate fraction
20% of plasma
so it may take 2 or 3 times to filter out a toxin
how much reabs per day?
48 gallons/day filtrates reabs to 1-2 qt urine
Net Filtration Pressure
NFP= total pressure that promotes filtration
NFP=GBHP - (CHP +BCO)
=10 mm Hg 55- (15+30)=10
if pressure higher, system wouldn’t work right
Glomerular Filtartion Rate (GFR)
amount of filtrate formed in all renal corpuscles of both kidneys/min
about 125 mL/min in adults (180 L/ day)
Homeostasis req for GFR
constant!
too high= loss of useful subastnaces due to speed of passage through nephron
too low= waste products may not be removed enough from body
GFR=
NFP= GHBP=CHP-BCOP mean arterial pressure-? afferent AP-> CHBP-> NFP-> GFR
what affects GFR?
changes in net filtration filtration stops of GBHP drops to 45 mm Hg (from 55) (45-45=0, nothing filtered out, just exits)
GHBP determined by…
MAP
kidney functions normally…
with MAP 80-180 mm Hg b/c of GFR reg
GFR Regulation
1) Autoregulation of GFR
2) Neural Regulation of GFR
3) Hormonal Regulation of GFR
Autoregulation of GFR
mechanisms that maintain constant GFR depiste arterial BP changes
myogenic mech
tubulogomerular feedback
myogenic mechanism
fast
systemic inc in BP stretch afferent arteriole
smooth muscle contraction reduces diameter of affernt arteriol,
GFR returns to pervious level in secs
tubuloglomerular feedback
slower
elevated systemic BP raises GFR, fluid flows to quickly through renal tubule (NA, Cl, water not reabsorbed)
macula densa in ascedning LH detects inc in NA and Cl,
inhibits relase of Nitric Oxide (vasodialer) from JG apparatus
afferent arterioles constrict, reduce GFR
Neural Regulation of GFR
blood vessles of kidney: supplied with symp fibers, cause vasoconstriction of affernt arterioles
Norepu relase from symp postgang binds alpha 1
adrenergic recprot-> vasocnstrict of affernt arteiroles
Neural Regulation of GFR
SNS overides renal autoreg if needed also stims renin release from JG cells
Neural Regulation of GFR: renal blood vessles at rest
maximally dialated b/c symp activity minimal (autoreg working)
Neural Regulation of GFR: moderate symp stim
both afferent and efferent arterioles constrict equally, dec GFR a little
Neural Regulation of GFR: exreme symp stim
exercise, hemmorahage
GFR dec a lot
lower urine output to maintain blood vol greater blood flow to tissues
Hormonal reg of GFR
atrial natruretic peptide (ANP) INCREASES GFR stretched ATRIA occurs with inc blood volume–> hormonal release relax GLOMERULA MESANGIAL cells–> inc glomerular capp SURFACE AREA and thus GFR
Hormonal reg of GFR and Angiotensin II
REDUCE GFR partly activated by renin from JG cells potent vasoconstricter-> narrows afferent and effernt arterioles, reduced GFR)
endothelial fenestrations of glmerulus
stops all cells and platelets (formed blood cells retaied)
basal lamina of glomerulus
stops large plasma proteins (they are retained)
slit membrane between pediceles
stops medium sized proetins, not small ones
NFP stands for
net filtration pressure
total pressure that promotes filtration
GBHP stands for and number
glomerular blood hydrostatic pressure
55 mm Hg
CHP stands for and number
capsular hydrostatuc pressuer 15 mmHG
BCOP stands for
blood colloid osmotic pressure
30 mmHG
filtration membrane
- endothelial fenestrations of glmerulus
- basal lamina of glomerulus
- slit membrane between pediceles all not stopped passes through
GBHP
pushes things out into capsular space
CHP
retarding push out
BCOP
trying to hold proteins into blood
ex of neural symp
norepi relase from symp post gang neuron
neurons bind to alpha 1adrenergic receptors
=vasconstrict afferent arterioles
