Physiology 3 Flashcards
What are the 3 barriers to glomerular filtration?
glomerular capillary endothelium; basement membrane and slit processe of podocytes
What is the glomerular capillary endothelium a barrier to?
RBCs
What are the basement adn glomerular epithlium barriers to?
plasma proteins
What are the 3 barriers known as collectively?
glomerular membrane
How does the basement membrane stop plasma proteins?
made up of GAGs and collagen which are collectively negatively charged which repels large negatively charged plasma proteins
What does glomerular filtration rely upon?
setting up a net filtration pressure as it is an entirely passive process
What is the biggest force determining net filtration pressure?
glomerular capillary blood pressure BPgc
What opposes glomerular capillary blood pressure?
Bowmans capsule hydrostatic (fluid) pressure HPbc
What is capillary oncotic pressure?
since there is a protein concentration gradient due to lack of proteins being filtered, they exert an osmotic effect to bring more water into the capillary
Why is Bowman’s Capsule oncotic pressure=0?
there aren’t any plasma proteins in the capsule lumen
What is GFR?
the rate at which protein-free plasma is filtered from the glomeruli into the Bowman’s Capsule per unit time
What is the equation for GFR?
Kf x net filtration pressure
What is Kf?
filtration coefficient- how holey the glomerular membrane is
What is normal GFR?
125 ml/min
What is the extrinsic regulation of GFR?
sympathetic control via baroreceptor reflex
What are the 2 factors that autoregulate GFR ?
myogenic mechanism and tubuloglomerular feedback mechanism
How does arterial blood pressure affect GFR?
increased BP increases blood flow into the glomerulus which increases BPgc; increasing net filtration pressure and increaseing GFR
What is the function of glomerular autoregulation?
prevents short term cahnges in systemic arterial pressure affecting GFR
What is the myogenic form of autoregulation?
vascular smooth muscle is stretched- due to increased BP; it contracts thus constricting the arteriole
What is the tubuloglomerular feedback mechanism?
involves juxtaglomerular apparatus- if GFR rises, more NaCl flows through the tubule leading to constriction of afferent arterioles (increased GFR would lead to increased tubular salt)
What part of the juxtaglomerular apparatus senses the salt content of tubular fluid?
macula densa
How does dehydration affect the GFR?
increases concentration of plasma proteins which increases capillary oncotic pressure, decreasing GFR
What is plasma clearance?
the volume of plasma completely cleared of a particular substance per minute
What is the equation for clearnace of substance X?
rate of excretion of X/ plasma conc. of X
What is the equation for the rate of excretion of X?
conc. of Xurine x Vurine (urine flow rate)
What substance has a clearance equal to GFR?
inulin
What substance has a clearance of 0?
glucose
If the clearance of a substance is less than GFR what does that suggest about the substance?
it is reabsorbed
What substance can be used to calculate renal plasma flow?
para-amino hippuric acid
What endogenous substance can be used to give a close approximation of GFR?
creatinine
What is filtration fraction?
fraction of plasma flowing through the glomeruli that is filtered into the tubules
What is filtration fraction equal to?
GFR/renal plasma flow
What is renal blood flow equal to?
RPF/1-Hct
