Lecture 11: CONTROLLING REGIONAL BLOOD FLOWS Flashcards
What does low pressure mean?
Lack of control of flow
What does high pressure mean?
Full control of flow
Why must high mean arterial pressure be maintained?
For full control over blood flow
What is the design of the systemic circulation?
Parallel
How is the arterial network in the systemic circulation?
Continually branching
What does the branching in the systemic circulation do?
Divides blood flow among the regional (organ) circulations
What does each organ receive?
An individual flow of blood which may be different to the flow of another organ
What is flow into an organ the same as?
The flow out of an organ
What is the total flow equal to?
All of the flows into individual organs added together
The total flow into the pulmonary and systemic circuits is …
the same
Where does blood flow to increase during exercise?
Muscle, heart and skin (so that heat can be lost)
Where does blood flow to decrease during exercise?
GI tract and kidneys
Where does blood flow to stay the same during exercise?
Brain
What does the diverging blood flow depend on?
The metabolic needs of the region/organ at that time
How is MAP controlled during exercise?
Cardiac output increases and so total peripheral resistance must decrease so that MAP is maintained
How does resistance to muscle, heart and skin change during exercise?
It decreases so that the blood flow is able to increase
How does resistance to the kidneys and GI tract change during exercise?
It increases so that blood flow is able to decrease
What is control of organ resistance and regional flow done by?
The resistance vessels - arterioles
What does a large radius mean?
Low resistance
What does a small radius mean?
High resistance
What is the rule of 16?
If the lumen changes by a factor of 2, the resistance will change by a factor of 16
What is blood flow to an organ or region controlled by?
Adjusting arteriolar (vascular) tone and radius
What does decreasing radius mean?
Smooth muscle contracts and the blood vessel vasoconstricts so there is less blood flow to the regions/organs
What does increasing radius mean?
Smooth muscle relaxes and the blood vessel vasodilator so there is more blood flow to the regions/organs
What is vasodilation and vasoconstriction used for?
To direct cardiac output
