Vascular Resistance and flow Flashcards
What is Ohms Law?
V = I x R
Pressure gradient = flow x resistance
What is the systemic cardiac output equation?
CO = (arterial Pressure - Venous Pressure) / Total peripheral resistance
What is the equation for local flow?
Flow = Change in pressure / Resistance
How is the total peripheral resistance calculated in series and give an example of when this might happen.
Total peripheral resistance = Resistances added together.
Eg:
Artery –> Arteriole –> Capillary –> Venule –> Vein
How is the total peripheral resistance calculated in parallel and give an example of when this might happen.
Total peripheral resistance = everything added together (inversed 1/)
eg:
Aorta –> organs in parallel –> vena cava
What happens to resistance when things are in parallel?
Resistance is reduced
What is the main site of resistance?
The arterioles
Radius of the arterioles has the biggest effect to control both flow into that tissue and peripheral resistance.
What is the distribution of cardiac output dependent on?
Dependent on local resistance
What causes a pressure difference?
Resistance causes a pressure difference upstream and downstream of the site of resistance.
What happens when blood flows through a resistance?
Pressure is lost when blood flows through a resistance
Why is systemic resistance important?
Role in setting blood pressure
Total peripheral resistance
Why is Local resistance important?
Role in changing tissue blood flow
Tissue vascular resistance
What is resistance proportional too?
Resistance is proportional to 1/ Radius of vessel ^4
How is blood vessel diameter controlled?
Via vasodilation and vasoconstriction
How is smooth muscle tone controlled?
by sympathetic nerves that cover the surface of the smooth muscle
What effect does sympathetic innervation have on flow rate?
Increase sympathetic activity - reduces flow rate by vasoconstriction.
Decrease sympathetic activity - increases flow rate via vasodilation
how do endothelial cells effect flow rate?
Nitric Oxide (NO) made in the endothelium by ENOS where it is then released into the smooth muscle as a gas and acts through cGMP to reduce Ca levels and thus decrease contraction leading to dilation
What causes vasoconstriction of smooth muscle in endothelial cells?
Endothelins increase the calcium ion concentration in the smooth muscle inducing more contraction and thus vasoconstriction.
What sets the tone of the smooth muscle in blood vessels?
The balance between the sympathetic nerves innervating the surface of the smooth muscle and the endothelial cell mechanisms within initiating contraction or dilation
What is endothelial dysfunction associated with?
Ageing
Why is local metabolic control of tissues important?
matches the metabolic rate in the tissue to the amount of blood flow through the tissue.
What is hyperemia?
Increase of blood flow
What is functional hyperemia?
When there is an increased blood flow due to increased metabolism to remove the metabolites.
Increase of blood flow is proportional to the needs of the body to remove the correct amount of metabolites.
What Is a recessive hyperemia?
When blood flow is cut off leading to a build up of metabolites. Then when the blood flow is resumed, this causes a sharp and rapid increase in blood flow (excess flow) to remove the build up of metabolites
How does a local myogenic mechanism work?
blood pressure increases and hence stretch channels open leading to Ca ion release. This leads to increased contraction and therefore vasoconstriction and thus increase resistance.
Why is a local myogenic mechanism important?
Ensures that when there is a pressure increase, there is always a constriction ensuring that flow remains constant.
(Autoregulation)
Which vasculature systems show the strongest autoregulation?
Cerebral and renal vasculature
How can hormones effect vascular tone?
Angiotensin II:
Renin (released from the kidney) acts on Angiotensinogen converting it to Angiotensin I, and then ACE (in lungs) converts this to Angiotensin II. Angiotensin II leads to vasoconstriction increasing blood pressure.
ADH (vasopressin) also acts as a vasoconstriction.
How does Adrenaline effect blood vessel diameter?
Low concentrations it would act on Beta 2 receptors and thus cause vasodilation. Often in skeletal muscle where Beta 2 receptors are located.
High concentration (if high enough) it would act on Alpha 1 receptors and potentially lead to vasoconstriction.
