CVPR Week 4: Microvascular control Flashcards
Objectives
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What mechanisms regulate organ blood flow?
local control mechanisms
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Locall control mechanisms of organ blood flow
- Autoregulation
- Hyperemia
Autoregulation of blood flow definition
to keep it constant
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Hyperemia blood flow definition
increasing blood flow
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Example of autoregulation
- when exercising the total blood flow increases and the % blood flow to the brain is reduced; however, the brain is still receiving the same amount of blood as it was at rest
- this is an example of autoregulation
![](https://s3.amazonaws.com/brainscape-prod/system/cm/273/118/065/a_image_thumb.jpg?1554332499)
Example of hyperemia`
During exercise the blood to the skeletal muscle is increased dramatically from at rest which is an example of hyperemia
Explain the autoregulatory mechanism of blood flow
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With increasing pressure how can blood flow remain constant?
by constricting or dilating vessels as specific
changes in resistance have the greatest impact on vascular resistance
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How does the autoregulatory mechanism regulate flow?
- an increase in perfusion pressure to the organ will cause an initial increase in blood flow and a stretch of the arterial smooth muscle cell wall
- stretch stimulates smooth muscle cells in that artery
- causes constriction
- causes increased resistance
- and reduces flow
- so this is a negative feedback to increased flow
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Myogenic mechanism
- The method of autoregulation
- AKA Bayliss effect
- receptors on the smooth muscle cells
- Mechanosensitive ion channel (MSC)
- Stretch-activated ion channels (SAC)
- sens the pressure and stretch and allow Ca2+ and Na+ into the cell and causes contraction
![](https://s3.amazonaws.com/brainscape-prod/system/cm/273/120/771/a_image_thumb.jpg?1554333280)
Bayless effect AKA
Myogenic mechanism or autoregulatory mechanism
A decrease in transmural pressure
- a reduction in perfusion pressure
- artery dilates
- reduces resistance and increases flow up to a steady-state level
![](https://s3.amazonaws.com/brainscape-prod/system/cm/273/120/818/a_image_thumb.jpg?1554333505)
Autoregulation description
- mediated by the myogenic response
- mechanism that maintains blood flow to the organs
How is local vascular resistance and blood flow regulated?
A balance of hemodynamic forces determines local vascular resistance and blood flow
- Shear stress causing relaxation
- Myogenic pressure causing contraction
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Explain active hyperemia
- Active hyperemia matches blood flow to the metabolic requirements = as metabolism goes up blood flow goes up, as it goes down blood flow goes down
- is associated with capillary recruitment and allow other capillary bed to open and precapillary sphincters will close to other capillary beds
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Congestion and hyperemia
- congestion is an increase in blood flow but it is due to an obstruction in outflow which doesn’t have new nutrients
- Hyperemia supplies tissues with new nutrients
![](https://s3.amazonaws.com/brainscape-prod/system/cm/273/121/139/a_image_thumb.jpg?1554333927)
What is hyperemia?
increase in blood flow due to greater demand during exercise, heat, digestion, inflammation or in response to ischemia
![](https://s3.amazonaws.com/brainscape-prod/system/cm/273/121/261/a_image_thumb.jpg?1554334000)
Explain reactive hyperemia
a transient increase in blood flow due to ischemia
not that the tissue is requiring more nutrients it just is not getting enough nutrients
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The magnitude of reactive hyperemia correlates with?
The duration of the occlusion is highly correlative to the magnitude and duration of the reactive hyperemic response is
“A repayment of nutrients to that tissue”
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Post-occlusion reactive hyperemia response (PORH)
is used as a measure of endothelial function
panel B is a good hyperemic response
Panel C is a bad hyperemic response and would indicate endothelial dysfunction
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There are some normal hyperemic responses in the body
Give an example
The endocardial arteries during systole has very low flow during systole so during diastole there is a hugh hyperemic response
This is why the are at a high risk for ischemia if there is endothelial dysfunction then the hyperemic response may be reduced leading to the ischemia
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The contribution of local blood flow mechanisms
4 listed
Metabolic dilation AKA active Hyperemic response
![](https://s3.amazonaws.com/brainscape-prod/system/cm/273/124/455/a_image_thumb.jpg?1554336029)
Skin local blood flow control mechanisms
Sympathetic nervous system and temperature
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Coronary local blood flow control mechanisms
- ↓ O2 causes dilation
- adenosine is an important dilator to increase blood flow
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Pulmonary local blood flow control mechanisms
↓O2 causes vasoconstriction
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Cerebral local blood flow control mechanisms
- Myoogenic
- CO2
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Skeletal local blood flow control mechanisms
- Sympathetic nervous system
- Metabolic
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Renal local blood flow control mechanisms
- Myogenic
- Tubuloglomerular
How is the cerebral circulation regulated
almost exclusively by local mechanisms
- Myogenic autoregulation - constant blood flow over a wide range of pressures
- metabolic regulations
- ↑CO2 or ↓O2 causes vasodilation and increase blood flow
- endothelial factors such as endothelin
- Sympathetic activity (very little under normal circumstances)
![](https://s3.amazonaws.com/brainscape-prod/system/cm/273/124/882/a_image_thumb.jpg?1554336499)
Cerebral blood flow control mechanisms
5 listed
- Myogenic autoregulation - constant blood flow over a wide range of pressures
- metabolic regulations
- ↑CO2 or ↓O2 causes vasodilation and increase blood flow
- endothelial factors such as endothelin
- Sympathetic activity (very little under normal circumstances)
Sympathetic control of cerebral blood flow
level of sympathetic activity modulates blood flow but doesn’t actually increase blood flow
![](https://s3.amazonaws.com/brainscape-prod/system/cm/273/124/953/a_image_thumb.jpg?1554336774)
Myogenic autoregulation of cerebral blood flow
![](https://s3.amazonaws.com/brainscape-prod/system/cm/273/125/104/a_image_thumb.jpg?1554336818)
Metabolic regulation of cerebral blood flow
![](https://s3.amazonaws.com/brainscape-prod/system/cm/273/125/185/a_image_thumb.jpg?1554336864)
What organs extracts the most O2 from the % available?
The heart extracts a lot of the available O2
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How does the heart get more nutrients
cannot really extract more O2 as the heart already pulls out a lot of blood
so
hypoxia causes dilation but also produces adenosine
adenosine binds to A1 and A2 causing various effects
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