Glomerular Filtration Flashcards
why are the kidneys so venerable to vascular disease?
they receive a high blood flow (20-25%) of cardiac output
what is the normal glomerular filtration rate?
125mls/min
what is the glomerular filtration dependent on?
balance between hydrostatic forces favouring filtration and oncotic pressure favouring reabsorption
what determines the filterability of solutes across the glomerular filtration barrier?
> molecular size
shape
electrical charge
what are the three layers of the filtration membrane?
> glomerular endothelial cells
basal lamina
slit membrane between podocytes
why is the glomerular capillary pressure higher than most capillaries?
the afferent arteriole is short and wide, offering little resistance to flow
describe to efferent arteriole in the glomerulu
long and narrow, offering a high post capillary resistance
true or false:
high resistance means there will be and increase in pressure up stream and a decrease in pressure downstream
true
at the glomerulus dos hydrostatic pressure exceed oncotic pressure?
yes as this favours filtration
what is the primary factor affecting GFR?
the hydrostatic pressure in the glomerular capillary
what is the extrinsic control of GFR?
> sympathetic vasoconstriction nerves
circulating catecholamines
angiotensin 2
what does circulating catecholiamines constrict?
the afferent capillary
what does angiotensin 2 constrict in the kidney?
> low: efferent
> high: afferent and efferent
how does renal vasculature intrinsically adjust its resistance?
autoregulation
what is the autonomic affect if the afferent arteriole in the kidney is the mean arterial pressure increases?
there is an increase in constriction to prevent rise in glomerular capillary pressure
what is the auto regulatory range in man?
60-130mmHg
in blood volume compromise (haemorrhage) describe the interaction between the intrinsic and extrinsic controls?
activation of the sympathetic vasoconstriction nerves and angiotensin 2 overrides autoregulation liberating more blood from the kidney to other important organs
true or false:
the hydrostatic pressure is very high in peritubular capillaries
false (the pressure is overcoming the frictional resistance in efferent arterioles)
in peritubular capillaries what is higher the oncotic pressure of the hydrostatic pressure?
oncotic pressure
how much of the plasma is filtered into the bowmans capsule?
20%
what is filtered at the glomerulus then reabsorbed within the tubule?
> 99% H2O
100% glucose
99.5% Na+
50% urea
