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
How does adenosine get formed?
When oxygen needs are not being met aerobic metabolism in the mitchondria is not very high so what happens is ADP and AMP accumulate and form adenosine which diffuses and vasodilates arterioles which increases blood flow in response.
What happens with skin blood flow when they are rubbed together?
The nutrient requirements of skin are low so temperature is causing the vasodilation. SNS instead of PSNS
How does blood flow to the brain get maintained at constant levels?
Autoregulation dominates. In animals that have been denervated the cerebral blood flow has been maintained regardless.
H+, K+, O2, adenosine, NO
paO2/CO2
At what level is blood flow to the brain maintained?
50ml/100g
How is blood flow regulated in the lungs?
Regulated by O2 levels in the alveoli.
In conditions of high O2 content blood vessels dilate and when O2 is low blood vessels constrict.
What is pulmonary BP like in pulmonary capillaries?
Low to encourage reabsorption
What happens if capillary pressure rises in the lungs?
Pulmonary oedema
How dense are capillaries in coronary arteries?
3000/mm2
Which is a ratio of 1 capillary to 1 cardiomyocyte. 1:1
What is the perfusion pressure like in coronary arteries?
Very high pressure due to being first off the aorta
Why does the heart have variable O2 requirements?
Due to changes in needs during different levels of activity
What is the diffusion distance between heart and capillaries?
9 micrometers
What is the oxygen extraction of the heart like?
Due to presence of lots of mitochondria the heart has 70 - 80% O2 extraction
When does the heart receive the most blood through coronary arteries? Why?
During diastole
Flow is prevented during diastole because of the high pressure compressing the CAs
What is an implication of the timing of filling of coronary arteries?
Due to the fact that coronary arteries transmit blood during diastole, the heart gets much less increase in blood perfusion during exercise despite the demand increase during exercise which means heart rate can’t increase past a certain limit.
How is vasodilation controlled in coronary arteries?
It increases proportionally due to local vasodilating factors. K+, H+, CO2, and bradykinin.
Also some neural regulation as a result of beta 2 receptor innervation of beta 2 receptors. Ach has a negligeble effect. The direct neural regulation of coronary blood flow is very small compared to that of the indirect effects resulting from elevated heart rate and contractility + autoregulation.
