Glomerular filtration Flashcards
(36 cards)
List the three basic renal processes.
Filtration
Reabsorption
Secretion
What % of the plasma volume passing through the glomerulus at any given time is filtered
20%
What is the blood filtering component of a nephron
Renal corpuscle
20% of the plasma volume passing through the glomerulus at any given time is filtered, what happens to the other 80%
passes via the efferent arterioles into the peritubular capillaries and then to the renal vein
Plasma makes up what % of blood volume
55%
Glomerular filtration rate > ?mls/min
> 90
Glomerular filtration is dependant on the balance between what forces
Hydrostatic forces (pushing fluid out capillary, i.e. favouring filtration)
and
Oncotic forces (favouring fluid into capillary, i.e. favouring reabsorption)
What is starling’s hypothesis
that the fluid movement due to filtration across the wall of a capillary is dependent on the balance between the hydrostatic pressure gradient and the oncotic pressure gradient across the capillary
Glomeruli are permeably selective on what solutes they allow cross the glomerular filtration barrier - what are some of the things considered
Molecular size
Electrical charge
Molecular shape
The fenestrated capillaries making up each glomerulus prevents filtration of what cells into the glomerulus
Blood cells - RBC/WBC etc
only allows plasma to get through
Why is glomerular capillary pressure higher than most other capillaries in the body
because the afferent arterioles making up the glomerulus is short and wide and so little resistance to flow so blood arriving has high hydrostatic pressure
Afferent arterioles are one of the final divisions of each segmental artery supplying the kidney, what do the afferent arterioles form
capillary network, i.e. the glomerulus
Efferent arterioles of the glomerulus are unlike the afferent arterioles - how?
long and narrow so offers a high post-capillary resistance
At the glomerular capillaries, the high capillary pressure means what starling’s force is favoured
hydrostatic pressure favouring filtration exceeds the oncotic pressure
Explain why normally only filtration occurs at the glomerular capillaries
because glomerular capillary pressure always»_space; colloid osmotic pressure gradient due to proteins in plasma (i.e. oncotic pressure)
so filtration always favoured
Factors affeting GFR
Glomerular capillary pressure
Glomerular capillary pressure is dependent on
afferent and efferent arteriolar diameter and therefore the balance of resistance between them
Afferent and efferent arteriolar diameter is extrinsically controlled by what 3 things
Sympathetic nerves –> constrict them
Catecholamines –> constrict them
Angiotensin II –> constrict efferent arterioles at low conc of angiotensin II at both at high conc.
If resistance is increased in afferent arteriole of the glomerulus, what does this mean for blood flow to other organs
increased blood flow to other organs
If renal blood flow is decreased, what do the efferent arterioles do in response to this to maintain GFR
increase their resistance so decreasing their diameter therefore increasing hydrostatic pressure to favour filtration and increase GFR
If resistance of afferent arterioles were decreased further (they already are low resistance), what does this mean for
- glomerular capillary pressure
- GFR
Glomerular capillary pressure increases so GFR increases
GFR can be maintained over what range of mean arterial BP
60-160mmHg
Below 60mmHg, what happens to GFR
Filtration rate decreases
If mean arterial BP increased, what would be the intrinsic response of the glomerulus to maintain GFR
afferent arteriolar constriction, preventing pressure rise from being transmitted to glomerular capillaries