BIOLOGY 3U03 Lecture Notes - Lecture 19: Oncotic Pressure, Afferent Arterioles, Blood Proteins
14 Dec 2016
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Professor
Hydrostatic pressure inside glomerular capillaries (PG)-
Promotes filtration
□
Hydrostatic pressure in Bowman's capsule (PB)- Opposes
filtration
□
Colloid osmotic pressure of glomerular capillary plasma
proteins (πG)- Opposes filtration
□
Considered zero due to low concentration of proteins
in glomerular filtrate
®
Colloid osmotic pressure of proteins in Bowman's capsule
(πB)- Promotes filtration
□
Yields
net filtration pressure
, which includes…
§
§
Sum of hydrostatic & colloid osmotic forces across glomerular membrane
○
Glomerular capillary filtration coefficient (Kf)
○
GFR is determined by…
•
Determinants of the GFR
Increased Glomerular Capillary Filtration Coefficient Increases
GFR
Increasing hydrostatic pressure in Bowman's capsule reduces GFR
•
E.g. "Stones" lodged in urinary tract obstruct outflow & raise Bowman's
capsule pressure-This reduces GFR
•
Increased Bowman's Capsule Hydrostatic Pressure Decreases GFR
As blood passed from afferent arteriole through glomerular capillaries to
efferent arterioles, plasma protein concentration increases BECAUSE ~
1/5th fluid in capillaries filters into Bowman's capsule, concentrating
glomerular plasma proteins that are NOT filtered
○
•
Increasing arterial plasma colloid pressure raises glomerular
capillary colloid osmotic pressure, which decreases GFR
§
Arterial plasma colloid osmotic pressure
○
Increasing filtration fraction concentrates plasma proteins & raises
glomerular colloid osmotic pressure
§
Thus, changes in renal blood flow can influence GFR
independently of changes in glomerular hydrostatic pressure
□
E.g. Reduction in renal plasma flow with no initial change in GFR
would increase filtration fraction-This would raise glomerular
capillary colloid osmotic pressure & reduce GFR
§
Even with constant glomerular hydrostatic pressure, greater
rate of blood flow into glomerulus tends to increase GFR &
lower rate of blood flow decreases GFR
□
Increasing renal blood flow results in lower fraction of plasma
filtered out of glomerular capillaries-This slows rise in glomerular
capillary colloid osmotic pressure --> Less inhibitory effect on GFR
§
Fraction of plasma filtered by glomerular capillaries (i.e. filtration
fraction = GFR/renal plasma flow)
○
Two factors influences glomerular capillary colloid osmotic pressure…
•
Increased Glomerular Capillary Colloid Osmotic Pressure
Decreases GFR
Changes in glomerular hydrostatic pressure serve as primary means for
physiologic regulation of GFR
•
BUT this is buffered to maintain constant glomerular
pressure as BP fluctuates
□
Increase tends to raise glomerular hydrostatic pressure & increase
GFR
§
Arterial pressure
○
Increased resistance of afferent arterioles reduces glomerular
hydrostatic pressure & decreases GFR
§
Afferent arteriolar resistance
○
As plasma protein concentration increases,
there is rapid, nonlinear increase in colloid
osmotic pressure caused by Donnan effect
(i.e. higher protein concentration, more
rapidly colloid osmotic pressure rises due
to interaction of ions bound to plasma
proteins)
}
Decrease occurs BECAUSE…
◊
Thus, if constriction severe, rise in colloid osmotic
pressure exceeds increase in glomerular capillary
hydrostatic pressure caused by constriction-Net force
for filtration then decreases
®
BUT BECAUSE efferent arteriolar constriction also reduces
renal blood flow, filtration fraction & glomerular colloid
osmotic pressure increase as efferent arteriolar resistance
increases
□
Constriction of efferent arterioles increases resistance to outflow
from glomerular capillaries-Raises glomerular hydrostatic pressure
& increases GFR
§
Efferent arteriolar resistance
○
○
Glomerular hydrostatic pressure is determined by three variable…
•
Increased Glomerular Capillary Hydrostatic Pressure Increases
GFR
Influenced by SNS, hormones, & autacoids (i.e. vasoactive substances
released in kidneys & act locally)
○
Most variable determinants of GFR are glomerular hydrostatic pressure &
glomerular capillary colloid osmotic pressure
•
Physiologic Control of Glomerular Filtration & Renal
Blood Flow
Strong activation of renal sympathetic nerves can constrict renal arterioles &
decrease renal blood flow & GFR
•
Most important in reducing GFR during severe, acute disturbances lasting
minutes-hours
•
Sympathetic Nervous System Activation Decreases GFR
BIO3UO3-Lecture 19
Friday,*December* 9,*2016
9:59*PM
Hydrostatic pressure inside glomerular capillaries (PG)-
Promotes filtration
□
Hydrostatic pressure in Bowman's capsule (PB)- Opposes
filtration
□
Colloid osmotic pressure of glomerular capillary plasma
proteins (πG)- Opposes filtration
□
Considered zero due to low concentration of proteins
in glomerular filtrate
®
Colloid osmotic pressure of proteins in Bowman's capsule
(πB)- Promotes filtration
□
Yields
net filtration pressure
, which includes…
§
§
Sum of hydrostatic & colloid osmotic forces across glomerular membrane
○
Glomerular capillary filtration coefficient (Kf)
○
GFR is determined by…
•
Determinants of the GFR
Increased Glomerular Capillary Filtration Coefficient Increases
GFR
Increasing hydrostatic pressure in Bowman's capsule reduces GFR
•
E.g. "Stones" lodged in urinary tract obstruct outflow & raise Bowman's
capsule pressure-This reduces GFR
•
Increased Bowman's Capsule Hydrostatic Pressure Decreases GFR
As blood passed from afferent arteriole through glomerular capillaries to
efferent arterioles, plasma protein concentration increases BECAUSE ~
1/5th fluid in capillaries filters into Bowman's capsule, concentrating
glomerular plasma proteins that are NOT filtered
○
•
Increasing arterial plasma colloid pressure raises glomerular
capillary colloid osmotic pressure, which decreases GFR
§
Arterial plasma colloid osmotic pressure
○
Increasing filtration fraction concentrates plasma proteins & raises
glomerular colloid osmotic pressure
§
Thus, changes in renal blood flow can influence GFR
independently of changes in glomerular hydrostatic pressure
□
E.g. Reduction in renal plasma flow with no initial change in GFR
would increase filtration fraction-This would raise glomerular
capillary colloid osmotic pressure & reduce GFR
§
Even with constant glomerular hydrostatic pressure, greater
rate of blood flow into glomerulus tends to increase GFR &
lower rate of blood flow decreases GFR
□
Increasing renal blood flow results in lower fraction of plasma
filtered out of glomerular capillaries-This slows rise in glomerular
capillary colloid osmotic pressure --> Less inhibitory effect on GFR
§
Fraction of plasma filtered by glomerular capillaries (i.e. filtration
fraction = GFR/renal plasma flow)
○
Two factors influences glomerular capillary colloid osmotic pressure…
•
Increased Glomerular Capillary Colloid Osmotic Pressure
Decreases GFR
Changes in glomerular hydrostatic pressure serve as primary means for
physiologic regulation of GFR
•
BUT this is buffered to maintain constant glomerular
pressure as BP fluctuates
□
Increase tends to raise glomerular hydrostatic pressure & increase
GFR
§
Arterial pressure
○
Increased resistance of afferent arterioles reduces glomerular
hydrostatic pressure & decreases GFR
§
Afferent arteriolar resistance
○
As plasma protein concentration increases,
there is rapid, nonlinear increase in colloid
osmotic pressure caused by Donnan effect
(i.e. higher protein concentration, more
rapidly colloid osmotic pressure rises due
to interaction of ions bound to plasma
proteins)
}
Decrease occurs BECAUSE…
◊
Thus, if constriction severe, rise in colloid osmotic
pressure exceeds increase in glomerular capillary
hydrostatic pressure caused by constriction-Net force
for filtration then decreases
®
BUT BECAUSE efferent arteriolar constriction also reduces
renal blood flow, filtration fraction & glomerular colloid
osmotic pressure increase as efferent arteriolar resistance
increases
□
Constriction of efferent arterioles increases resistance to outflow
from glomerular capillaries-Raises glomerular hydrostatic pressure
& increases GFR
§
Efferent arteriolar resistance
○
○
Glomerular hydrostatic pressure is determined by three variable…
•
Increased Glomerular Capillary Hydrostatic Pressure Increases
GFR
Influenced by SNS, hormones, & autacoids (i.e. vasoactive substances
released in kidneys & act locally)
○
Most variable determinants of GFR are glomerular hydrostatic pressure &
glomerular capillary colloid osmotic pressure
•
Physiologic Control of Glomerular Filtration & Renal
Blood Flow
Strong activation of renal sympathetic nerves can constrict renal arterioles &
decrease renal blood flow & GFR
•
Most important in reducing GFR during severe, acute disturbances lasting
minutes-hours
•
Sympathetic Nervous System Activation Decreases GFR
BIO3UO3-Lecture 19
Friday,*December* 9,*2016 9:59*PM
Document Summary
Sum of hydrostatic & colloid osmotic forces across glomerular membrane. Hydrostatic pressure in bowman"s capsule (pb)- opposes filtration. Colloid osmotic pressure of glomerular capillary plasma proteins ( g)- opposes filtration. Colloid osmotic pressure of proteins in bowman"s capsule ( b)- promotes filtration. Considered zero due to low concentration of proteins in glomerular filtrate. Increasing hydrostatic pressure in bowman"s capsule reduces gfr. stones lodged in urinary tract obstruct outflow & raise bowman"s capsule pressure- this reduces gfr. As blood passed from afferent arteriole through glomerular capillaries to efferent arterioles, plasma protein concentration increases because ~ 1/5th fluid in capillaries filters into bowman"s capsule, concentrating glomerular plasma proteins that are not filtered. Two factors influences glomerular capillary colloid osmotic pressure . Increasing arterial plasma colloid pressure raises glomerular capillary colloid osmotic pressure, which decreases gfr. Fraction of plasma filtered by glomerular capillaries (i. e. filtration fraction = gfr/renal plasma flow) Increasing filtration fraction concentrates plasma proteins & raises glomerular colloid osmotic pressure.
