Peripheral circulation Flashcards
What happens if all arterioles in the body were dilated?
Flow needed to maintain the BP would be 3 - 4 times maximum CO
Where does blood get shifted when parasympathetic NS is dominant?
Digestive tract, liver, kidneys
What happens to blood circulation during exercise?
It all goes to muscles with a much smaller proportion going to the other organs
What happens to intercranial pressure when BP is very high? What does this mean?
It increases to dangerous levels. This means blood flow is maintained relatively well to the brain.
What happens to heart blood flow during exercise?
It is increased significantly
What does the sympathetic NS do to redistribution of the blood?
It decreases blood flow to kidneys, GI, and liver.
Rest of the organs are affected more by local factors
What are anastomoses?
Alternate routes for blood flow
What is the difference between arterial and A-V anastomoses?
Arterial anastomses (are capillaries within an area supplied by arteries called collaterals that fuse together and interconnect.
A-V anastomses skip capillary beds altogether
Why don’t tissue die due to lack of blood flow in anastomoses?
Because the redirected blood is dynamic and goes from one capillary bed to another dynamically
How is tissue perfusion regulated?
Systemic control mechanisms through neural (for short term regulation) and endocrine control mechanisms (for long term regulation)
Autoregulation (Cause immediate localised homeostatic adjustments)
Which tissue use a lot of local mechanisms for blood perfusion regulation?
Skeletal muscle (adenosine from all phosphates in ATP being knocked off is an example)
What are some systemic mechanisms for changing vessel diameter?
Vasoconstriction:
NorAdrenaline (symathetic post ganglionic neurones)
Serotonin
ADH
AtII
Systemic control for
Vasodilation:
Adrenaline (beta 2 receptors in lungs, skeletal muscle and heart)
ACh (only in the bloodstream which is rare because it requires them to spill over from synapses)
ANP (Vasodilator)
VIPs (Vasoactive intestinal peptides from neurones (enteric NS))
What causes autoregulation of blood flow?
Metabolites are used to adjust local blood perfusion to demands.
What are the 2 types of stimuli for vasodilation at the local level?
Physical: From temperature changes and myogenic response (stretch response)
Hyperaemia: Vasodilating chemicals alter blood vessel diameter
What is myogenic autoregulation?
Counteracts imposed change
If the pressure in a vessel is suddenly increased the vessel responds by constricting
Diminishing pressure within vessel causes relaxation and vasodilation
What are the types of hyperaemia?
Active: When metabolism is increased the metabolites produced act as vasodilators
Reactive: Occlusion causes a tissue to get less blood and starve. Byproducts accumulate and result in vasodilation which overcomes the starvation.
What type of chemical messengers are the local vessel controls?
Paracrine chemicals
What are some local vessel controlling vasoconstrictors?
Serotonin (secreted by activated platelets)
Endothelin (secreted by vascular endothelium in response to damage)
What are some local vessel dilators?
NO secreted by vascular endothelium
Bradykinin
Histamine (from mast cells = damage)
Adenosine secreted by cells in low O2 conditions (ATP breaks down into this)
Metabolites such as drop in O2 or a rise in CO2, potassium, acid, temperature, and lactate.
Why would local vasoconstrictors be so useful?
To respond to damage
When are histamine and bradykinin produced?
During the inflammatory process
How is vasoactive NO produced?
by NOS using arginine
What does NO do?
it is a smooth muscle relaxant which dilates smooth muscle of arterioles nearby
How can adenosine act as a local vasodilator?
Unlike ATP, adenosine has no problem diffusing across the plasma membrane. ATP is inhibited by the plasma membrane due to the high polarity that the phosphate groups give it
