Functional perfusion of the kidney Flashcards
Which organ has the highest blood flow per unit mass?
The kidneys
What is the average blood flow to the kidney?
1200 mL/min
What is the average plasma flow to the kidney?
650 mL/min
What percentage of the cardiac output goes to the kidney?
25% of the cardiac output
What percentage of body weight do the kidneys make up?
Less than 0.5% of the body weight
How does the renal circulation divide in the kidneys?
Renal artery -> interlobar arteries -> arcuate arteries -> interlobular arteries -> afferent arterioles that perfuse the glomerulus
How many interlobar arteries form from the division of the renal artery?
5 per kidney
Along where do the interlobar arteries run on the structure of the kidney?
Up the side of the renal pyramids
Where on the renal structure do the interlobar arteries divide into the arcuate arteries?
In the border of the medulla and cortex
Why do the kidneys have such high blood flow?
Kidneys need to filter 180 litres a day to maintain homeostasis
The kidney is the organ with the highest oxygen uptake
TRUE or FALSE
FALSE
The kidney has the second highest oxygen uptake - after the heart
Kidneys have the lowest atriovenous oxygen difference in any organ due to its high blood flow
TRUE or FALSE
TRUE
What is the Glomerular Filtration Rate?
Filtration of the renal plasma from the glomerula capillaries into the Bowman’s capsule
What is the typical value for GFR?
120 mL/min
What is GFR used for?
Best single means of assessing kidney function
What is autoregulation?
Method by which the kidney’s GFR and renal blood flow remains constant despite an increase in systemic pressure
Why is autoregulation necessary?
Prevents changes in systemic pressure from affecting renal function
Increase in systemic pressure results in no increase in GFR or renal blood flow
What is the correlation between renal blood flow and GFR?
Direct correlation
Within what range of systemic BP will autoregulation work?
90 - 180 mmHg
What are the two mechanisms of autoregulation?
Myogenic mechanism
Tubuloglomerular feedback
Which mechanism of autoregulation acts faster?
Myogenic mechanism
What is the myogenic mechanism?
Intrinsic capacity of the smooth muscle cells in the afferent arterioles to constrict when distended
Describe the steps of the myogenic mechanism
Blood pressure increases
Afferent arterioles stretch
Non-specific cation channels open
Depolarization
Calcium channels open
Afferent arteriole contracts
What is the stimulus of the tubuloglomerular feedback?
Concentration of sodium in the DCT
What is the stimulus of the myogenic mechanism?
Blood pressure of the afferent arteriole
What apparatus regulates the tubuloglomerular feedback?
The juxtaglomerular apparatus
Describe the steps of the tubuloglomerular feedback
Blood pressure increases
Afferent arteriole pressure increases
GFR increases
Increased sodium delivery to the DCT
Macula densa cells detect an increase in sodium concentration and release adenosine
Afferent arterioles contract
What is adenosine?
A purine that acts on purinergic receptors on arterioles
Which mechanisms can override autoregulation?
Nerves
Hormones
Within which range does autoregulation function?
90 - 180 mmHg
In which situations do nerves override autoregulation?
In situations of stress or limit of water loss from body
Reduction of blood flow to the kidneys
How do nerve override autoregulation?
Causes afferent and to some degree efferent arteriolar constriction
Reduces renal blood flow and GFR
Hormones override autoregulation in response to which situations?
Reduced pressure in the afferent arteriole
Increased sympathetic nerve stimulation
Decreased sodim in the distal tubule sensed by Macula densa cells
Example of hormones that override autoregulation
Renin-angiotensin system
Which cells produce renin?
Renin is produced by granular cells located along afferent arterioles in kidneys
What are the steps of the renin-angiotensin system?
- Renin is released from macula densa cells in the afferent arteriole
- Angiotensinogen is released from the liver
- Renin acts on Angiotensinogen - converts it to angiotensin I
- Capillary endothelial in lungs release ACE
- ACE converts Ang I - Ang II
- Ang II has various effects
What are the effects of Angiotensin II on the pituitary gland?
Causes release of ADH from the pituitary gland
What are the effects of Angiotensin II on the adrenal gland?
Releases aldosterone which affects sodium and water reabsorption
What are the effects of Angiotensin II on autoregulation?
Overrides autoregulation
Can affect both the afferent and efferent arterioles - most receptors are found on the efferent
Causes vasoconstriction
What are the consequences of vasoconstriction of the renal arterioles?
Reduce renal blood flow through the capillaries
Increases pressure in the capillaries
Increases GFR
What is the consequences of high Ang II concentration?
Vasoconstriction of both afferent and efferent arterioles
When is Ang II released in high concentration?
After a haemorrhage
Makes blood flow away from the kidney and to other important organs
Reduces GFR and renal blood flow
What are the consequences of renal blood flow and GFR following low conc of Ang II vs high conc of Ang II release?
Low concentration - efferent vasoconstriction. GFR increases whilst blood flow decreases
High concentration - afferent and efferent vasoconstriction. GFR and blood flow decrease
