3 - renal filtration, reabsorption and secretion Flashcards
3 basic renal processes?
filtration
reabsorption
secretion
where does filtration take place?
glomerulus
~% of plasma is in the filtrate?
20%
normal GFR?
180 litres/day
125ml/min
benefit of normal GFR being very high?
ample opportunities to -
regulate ECF volume and composition
eliminate harmful substances
reabsorption in the PCT?
NaCl
H2O
amino acids
sugars
reabsorption in the DCT?
NaCl
H2O
purpose of secretion?
to specifically remove harmful substances
why can damage to kidneys be lethal?
large blood supply and cardiac output
consequence of having large cardiac output on the kidneys?
increased vulnerability of vascular disease
how much cardiac output do the kidneys receive?
20-25%
renal plasma flow?
660mls/min
function of hydrostatic forces?
favours filtration by pushing blood into bowman’s capsule
function of oncotic pressure forces?
favours reabsorption
3 factors affecting the permselectivity of the glomerular barrier and substances being absorbed?
molcular size
electrical charge
shape of molecule
what is the filtration fraction?
GFR / renal plasma flow x100
why is Pgc higher than other capillaries?
due to the low resistance of the afferent arterioles
what maximises pressure conditions within bowman’s capsules?
afferent arterioles being short, wide and therefore low resistance and pressure
AND
efferent arterioles being long, narrow and therefore high resistance and pressure
Pgc - what is it always higher than and what is the result of this?
always higher than oncotic pressure -
therefore, filtration is always favoured
golden rule of circulation?
high resistance causes increased hydrostatic pressure upstream while decreasing pressure downstream
what occurs at glomerular capillaries?
ONLY filtration
1y factor affecting GFR?
Pgc - which is dependent on afferent and efferent arteriolar diameter
3 extrinsic factors affecting GFR?
sympathetic nerves
circulating catecholamines
angiotensin II
effect of sympathetic n on GFR?
afferent and efferent vasoconstriction
effect of circulating catecholamines on GFR?
afferent vasoconstriction
effect of angiotensin II on GFR?
vasoconstriction of efferent at low concentrations,
vasoconstriction of efferent AND afferent at high concentrations
result of increase in resistance of afferent arteriole?
decreased pressure of capillary blood
-> decreased GFR
result of increase in resistance of efferent arteriole?
increased pressure of capillary blood
-> increased GFR
result of decrease in resistance of afferent arteriole?
increased pressure of capillary blood
-> increased GFR
normal range of BP?
60-130 mmHg
what occurs when BP <60mmHg?
glomerular filtration decreases
what occurs when BP=50mmHg?
glomerular filtration stops altogether
result of increasing mean arterial pressure?
increased afferent arteriole constriction and therefore decreased pressure of capillary blood
is auto regulation dependent on anything?
it is independent of nerves and hormones and it occurs in denervated and isolated kidneys
what plays an important role in auto regulation?
blood volume
reabsorption of peritubular capillaries - describe the efferent arterioles relationship to hydrostatic pressure?
efferent arterioles are long and narrow, therefore increasing the resistance and pressure
this decreases the pressure of the blood and so the hydrostatic pressure also decreases to ~15mmHg
