Physiology - Glomerular Filtration and Renal Blood Flow Flashcards
which has a larger diameter - the afferent or efferent arteriole?
afferent
what are the three barriers to filtration?
glomerular capillary endothelium
basement membrane
slit processes of podocytes
what is the glomerular capillary endothelium a barrier to?
red blood cells
what is the basement membrane a barrier to?
plasma proteins
what are podocytes a barrier to?
plasma proteins
what is another name for the basement membrane?
the basal lamina
what is the basement membrane made of?
collagen
glycoproteins
it is acellular
how does the basement membrane form a barrier ti plasma proteins?
it confers a net negative charge, stopping the positively charged proteins passing through
does glomerular filtration require energy?
no - it is completely passive
what two pressures favour filtration in the glomerular capillary?
glomerular capillary blood pressure
bowman’s capsule oncotic pressure
what two pressures oppose filtration in the glomerular capillary?
bowman’s capsule hydrostatic pressure
capillary oncotic pressure
what is the normal net filtration pressure in the glomerular capillary?
10 mmHg
overall, filtration is favoured
what is the normal value for bowman’s capsule oncotic pressure and why?
zero
there are no plasma proteins in the bowman’s capsule to create the pressure
what is another name for oncotic pressures?
colloid osmotic pressures
what is GFR?
the rate at which plasma is filtered from the glomeruli into the bowman’s capsule per unit time
how do you calculate GFR?
Kf x net filtration pressure
what is Kf?
the filtration coefficient
a measure of how permeable the membrane is
what is the normal value for GFR?
125 ml/min
what is the extrinsic regulation of GFR?
sympathetic control via the baroreceptor reflex
what effect does increased blood pressure have on GFR regulated by baroreceptors?
increased capillary blood pressure, increased filtration pressure, increased GFR
what is another name for intrinsic regulation of GFR?
autoregulation
what are the two mechanisms for autoregulation of GFR?
myogenic mechanism
tubuloglomerular feedback mechanism
how does the myogenic mechanism control GFR?
if vascular smooth muscle is stretched by increased blood pressure, it automatically contracts
this regulates the blood flow to the glomerular kidney
what type of feedback loop is the tubuloglomerular feedback mechanism?
negative feedback
how does the tubuloglomerular feedback mechanism control GFR?
if GFR rises, more NaCl flows through the tubules and the macula densa releases vasoconstrictive mediators
this causes constriction fo afferent arterioles and a decrease in GFR
what is BPGC?
the glomerular capillary blood pressure
promotes filtration
what is COPGC?
capillary oncotic pressure
opposes filtration
what is HPBC?
bowman’s capsule hydrostatic pressure
opposes filtration
what is COPBC?
bowman’s capsule oncotic pressure
promotes filtration
what could increase the HPBC and what effect does this have on GFR?
kidney stones
reduces GFR
what could increase the COPGC and what effect does this have on GFR?
diarrhoea
reduces GFR
what could decrease the COPGC and what effect does this have on GFR?
severe burns
increases GFR
what effect does decreased Kf have on GFR and what could cause this?
decreased GFR
a change in the surface area available for filtration
what is plasma clearance a measure of?
how effectively the kidneys can clean the blood of a substance
what is plasma clearance and what are its units?
the volume of plasma completely cleared of a substance per minute
ml/min
what is the plasma clearance of inulin?
the same as GFR
why is no glucose normally found in the urine?
it is freely filtered and then completely reabsorbed, so none is secreted
what is the plasma clearance value for glucose?
zero
compared to GFR, what is the plasma clearance for urea?
less than GFR
what happens to urea in the nephron?
filtered
partly reabsorbed
not secreted
what happens to hydrogen in the nephron?
filtered
secreted
not reabsorbed
compared to the GFR, what is the clearance of hydrogen?
greater than GFR
what does PAH stand for and what is it?
para-amino hippuric acid
an exogenous organic anion
what is PAH used for?
calculating renal plasma flow (RPF)
what is the filtration fraction?
the fraction of plasma flowing through the glomeruli that is filtered into the tubules
how do you calculate the filtration fraction?
GFR/renal plasma flow
what is the filtration fraction in a healthy adult?
20%
means that 20% of the plasma that enters the glomeruli is filtered
