Control of GFR Flashcards
What is autoregulation of GFR?
Refers to intrinsic mechanisms in the kidney that maintain GFR with changes in arterial blood pressure
What range of arterial blood pressure does autoregulation of GFR function at?
80 - 180mmHg
What are the mechasnisms of autoregulation of GFR?
Myogenic mechanisms
Tubular glomerular feedback
What is meant by myogenic mechanisms?
Refers to how the smooth muscle in the walls of the afferent
arteriole can contract or relax in response to changes in arterial blood pressure
How does an increase in arterial blood pressure affect GFR immediately?
Increases glomerular hydrostatic pressure
increases GFR
With an increase in arterial blood pressure, what does the smooth muscle in the wall of the afferent arteriole detect?
Detects stretch
How does the smooth muscle in the wall of the afferent arteriole respond to stretch?
Contracts
giving vasoconstriction
How does vasoconstriction of the afferent arteriole affect GFR?
Increases resistance to blood flow through afferent arteriole
reduced blood flow through afferent arteriole, glomerular capillary
reduced glomerular hydrostatic pressure
reduced GFR
How does a decrease in arterial blood pressure affect GFR immediately?
Decreases glomerular hydrostatic pressure
decreases GFR
With a decrease in arterial blood pressure, what does the smooth muscle in the wall of the afferent arteriole detect?
Lack of stretch
How does the smooth muscle in the wall of the afferent arteriole respond to lack of stretch?
Relaxes
giving vasodilation
How does vasodilation of the afferent arteriole affect GFR?
Decreases resistance to blood flow through afferent arteriole
increased blood flow through afferent arteriole, glomerular capillary
increased glomerular hydrostatic pressure
increased GFR
What is tubular glomerular feedback?
Refers to how the macula densa in the distal convoluted tubule
can affect the state of the afferent and efferent arterioles
What do the macula densa cells detect?
Detect changes in the concentration of sodium chloride in the distal convoluted tubule
How do the macula densa cells detect the concentration of sodium chloride in the distal convoluted tubule?
Based on the activity of the sodium chloride transporter on the apical domain of epithelial cells in the distal convoluted tubule
What causes an increase in the concentration of sodium chloride in the distal convoluted tubule?
Increased GFR
more sodium chloride filtered out of the glomerular capillary into Bowman’s capsule
How do the macula densa cells respond to an increase in sodium chloride concentration in the distal convoluted tubule?
Release adenosine
What does adenosine released by the macula densa cells bind to?
Binds to A1 receptors in the afferent arteriole
Binds to A2 receptors in the efferent arteriole
What does adenosine binding to A1 receptors in the afferent arteriole result in?
Contraction of smooth muscle in afferent arteriole wall
giving vasoconstriction
What does adenosine binding to A2 receptors in the efferent arteriole result in?
Releaxation of smooth muscle in efferent arteriole wall
giving vasodilation
What causes a decrease in the concentration of sodium chloride in the distal convoluted tubule?
Decreased GFR
less sodium chloride filtered out of the glomerular capillary into Bowman’s capsule
How do the macula densa cells respond to a decrease in sodium chloride concentration in the distal convoluted tubule?
Release prostagladins
What do prostaglandins released by the macula densa cells do?
Give smooth muscle in wall of afferent arteriole to relax
vasodilation of afferent arteriole
How do adenosine and prostaglandins released by the macula densa cells reach the afferent and efferent arterioles?
Glomerulus is very close to distal convoluted tubule
so the adenosine and prostaglandins only hae to travel a short distance
Why is GFR regulated?
To prevent changes in arterial blood pressure
giving large changes in the amount of ions, water that are excreted
What sort of changes in arterial blood pressure is autoregulation of GFR involved in?
Acute short-term changes in blood pressure
What innervates the smooth muscle in the walls of the afferent and efferent arterioles?
Sympathetic nerve fibres
What can cause the sympathetic nerve fibres to stimulate the smooth muscle in the walls of the afferent arterioles?
Fight or flight response
Haemorrhage that is severe
What does sympathetic stimulation of the smooth muscle in the walls of the afferent arterioles cause?
Contraction of smooth muscle
giving vasoconstriction
reduced GFR
What is the purpose of the sympathetic stimulation causing vasoconstriction of afferent arterioles?
Conserve blood volume
