Glomerular filtration Flashcards
What are the 3 basic renal processes
filtration
reabsorption
secretion
Give some examples of substances reabsorbed
sodium chloride, water, glucose, amino acids
Give some examples of substances secreted
organic ions, drugs,
How much of the cardiac output do the kidneys receive and what is the significance of this?
20-25%
vulnerability to damage by vascular disease
What tissue in the body has the highest BF/g?
kidneys!
Why does the kidneys receive such a large blood flow?
filtration! - not for oxygen
How long does it take for the volume for the total BV to pass through the renal circulation?
5 mins
Are red cells filtered into bowmans capsule?
no
What is the renal plasma flow?
660mls/min
What is the % filtration fraction?
19% - usually say 20
What is glomerular filtration dependent on the balance between?
starling’s forces
hydrostatic and oncotic pressures
Which of hydrostatic and oncotic pressure favours reabsorption and which favours filtration?
Hydrostatic - filtration
oncotic - reabsorption
3 things the permeselectivity of glomerular barrier is dependent on
molecular size, charge and shape
How does the glomerulus make sure proteins don’t get filtered
fenestration pore - prevents filtration of blood cells only
basal lamina - prevents filtration of larger proteins
slit membrane between pedicles - prevents filtration of medium proteins
Is the glomerular capillary pressure higher or lower than most capillaries? why?
higher
afferent arteriole - short and wide and little resistance
Does the blood arriving at the glomerulus have high or low hydrostatic pressure?
high
What is the efferent arteriole of the glomerulus like?
long and thin and high post capillary resistance
If there is high resistance what happens to hydrostatic pressure upstream and downstream?
upstream increases
downstream decreased
Why does only filtration occur at glomerular capillaries?
afferent and efferent arterioles contribute to high glomerular capillary hydrostatic pressure. This pressure always exceeds oncotic pressure and so only filtration occurs.
primary factor affecting GFR
PGC - dependent on arteriolar diameter and resistance
3 extrinsic controls affecting GFR
angiotensin 2
sympathetic VC nerves
catecholamines
Is the afferent or efferent arteriole more sensitive to sympathetic VC control?
afferent
How do circulating catecholamines affect the GFR?
constrict primarily the afferent arteriole
What does angiotensin 2 do to the glomerular arterioles?
constrict efferent at [low] and both at [high]
What is meant by autoregulation in terms of the renal vasculature?
intrinsic ability to adjust resistance in response to arterial bp changes
keep BF and GFR relatively constant
What mbp is autoregulation effective over? when does it fall and when does it cease?
60-130mmHg
below 60
50
What happens to the afferent arteriole if the MAP increases
increase in constriction and prevent a rise in glomerular PGC
Is autoregulation dependent or independent of hormone and nerves?
independent
In haemorrhage what can override autoregulation? why?
extrinsic controls eg sympathetic VC and A2
liberates blood for more immediately important organs
How much blood can be directed elsewhere in expense of the kidneys?
800ml/min
What happens in prep for a marathon to prevent taking away from kidney BF
adaption of skeletal muscle to become more efficient
What volume of blood per day is
a - filtered at glomerulus
b - excreted
180l
1-2l
Why does only reabsorption take place in the efferent arteriole?
oncotic pressure exceeds hydrostatic as 20% volume ahs been removed and is now more concentrated with proteins
