4 - glomerular filtration Flashcards
what is the daily GFR?
180L/day
C.O. - how much do kidneys receive?
25%
what is the result of kidneys receiving huge amount of C.O.?
they’re vulnerable to vascular disease
what is passed though to Bowman’s capsule?
no RBCs and a fraction of plasma
what happens to the material which does not filter through the bowman’s capsule?
passes via efferent arterioles into the peritubular capillaries - then to renal v
how much of the blood vol is plasma?
55%
how to work out filtration fraction?
work out 55% of 1200 = 660 pls/min (renal plasma flow)
then 125/660x100 = 19%
what is the renal plasma flow?
this is the % of plasma in BV x 1200mls/min -
55% of 1200 = 660
what is glomerular filtration dependent on?
balance between hydrostatic forces and oncotic pressure
what do hydrostatic forces favour?
filtration
what does oncotic pressure favour?
reabsorption
name 3 things which affect the filterability of solutes across the glomerular filtration barrier?
molecular size
electrical charge
shape
what is the function of the fenestration of the glomerular endothelial cell?
prevents filtration of blood cells but allows all components of blood plasma to pass through
function of basal lamina of glomerulus?
prevents filtration of larger proteins
function of slit membrane pedicles?
prevents filtration of medium sized proteins
compare pressure of capillaries and the glomerular capillary pressure (Pgc)?
Pgc is much higher
why is the Pgc much higher than that of the pressure of other capillaries in the body?
the afferent arteriole is short and wide and offers little resistance to flow -
therefore blood arriving at glomerulus still has a high hydrostatic pressure
result of the efferent arteriole’s structure?
structure is long and narrow and so offers a high post-capillary resistance -
therefore blood at glomerulus has low hydrostatic pressure
golden rule of circulation?
if there is high resistance, hydrostatic pressure upstream is increased and pressure downstream is decreased
what occurs at the glomerular capillaries?
filtration ONLY
what is net filtration pressure?
10mmHg
what is the 1y factor affecting GFR?
Pgc - dependent on the afferent and efferent arteriolar diameters ant therefore the balance between them
sympathetic VC nerves - effect on GFR?
leads to afferent and efferent constriction, greater sensitivity of afferent arteriole
circulating catecholamines - effect on GFR?
constriction of primary afferent angiotensin II
-> leads to constriction of efferent arterioles at low concentration, and efferent and afferent at high concs.
reabsorption?
Substances that the body wants are reabsorbed -
those it doesn’t want stay in the tubule
and are excreted
secretion?
Substances may be specifically removed from the body in this way
auto regulation of BP?
via control and adjusting of resistance in response to changes in arterial BP
range of mean BP?
60-130mmHg
what happens when BP falls below 60mmHg?
filtration falls or ceases altogether (50 and below)
what happens when there is an increase in MAP?
there is an automatic increase in afferent arteriolar constriction, preventing a rise in glomerular Pgc
what occurs as MAP decreases?
dilation
where does auto regulation occur and what is its control?
control - independent of nerves or hormones
occurs in denervated and isolated perfused kidneys
what happens when blood vol/ BP face a steroid compromise?
activation of sympathetic VC nerves overrides auto regulation -
leads to availability of blood for organs which need it most
how much blood can be spared at the expense of the kidneys?
up to 800mls
result of prolonged exposure to steroid compromise?
reduces renal blood flow for prolonged period -
- > irreparable damage to kidneys
- > death (due to dysfunction of homeostasis)
