Lecture 8 Flashcards
Arteries can be described as __________ tubes
multilayered tubes
Arteries and arterioles both have ____________
endothelium
Arteries have more ________ __________ whereas arterioles have more _______ ________
elastic tissue
smooth muscle
How is the smooth muscle arranged in an arteriole?
It wraps around the endothelium
What are the two main functions of aorta and large arteries?
- distribute blood
- act as a pressure reservoir
What does it mean when the aorta and large arteries act as a pressure reservoir?
They reduce fluctuations in pressure and flow and maintain flow throughout the cardiac cycle
When the blood is ejected, it travels through the aorta. Describe how the structure of them helps with its function
The aorta has lots of elastic tissue so it can change its shape which helps its function of being a pressure reservoir. Some of the blood stretches the walls of the artery which means it stores potential energy so then during diastole it springs back
Why does the blood go to the periphery and not back into the heart during diastole?
because the semilunar valves are shut
During systole, the aorta ______ potential energy
stores
During diastole, the aorta __________ the energy
releases
What does compliance mean?
stretchiness
What is the equation for compliance?
ΔV/ΔP
What is the opposite of compliance?
stiffness
What is the equation for stiffness?
1/compliance
How does the structure of the aorta/artery change with age and how does this affect its compliance?
A young artery is very compliant whereas an old artery has more collagen and muscle wall which makes it less compliant. This changes its ability to recoil which means that less blood can flow around the capillary
Describe the structure of the aterioles
They have smooth muscle wrapper around the lumen
What is the purpose of the smooth muscle that wraps around the lumen of the arterioles?
It can contract and relax to alter the diameter of the arterioles
What is vasoconstriction and what causes it?
this is when the smooth muscle wrapped around the lumen of the arterioles contracts which reduces the diameter of the arteriole
What is vasodilation and what causes it?
this is when the smooth muscle wrapped around the lumen of the arterioles relaxes which increases the diameter of the arteriole
What is the purpose of vasodilation and vasoconstriction?
to control resistance and therefore control local flow
We have pulsatile blood pressure across the ________ and then this drops in the _________
arteries
arterioles
What is diastolic pressure?
This is the minimum pressure just before ventricle contraction
What is systolic pressure?
this is the maximum arterial pressure reached during peak ventricular ejection
What are the normal values for blood pressure?
120 (SP)/80 (DP) mmHg
What is hypertension?
this is high blood pressure (values over 140/90 mmHg)
What is hypotension?
this is low blood pressure (values under 90/60 mmHg)
What causes the dicrotic notch?
this is during the declining pressure phase, there is a little blip because the aortic valve closes and there is a small increase in pressure
How do we calculate mean arterial blood pressure?
DP + (1/3)(SP - DP)
What is the pulse pressure and how is it calculated?
this is the difference between systolic pressure and diastolic pressure (SP - DP)
Why do we need MAP to be maintained at such a precise point?
so that we can perfuse all the tissues
What are the two determinants of mean arterial blood pressure?
Q (cardiac output) x TPR
We can adjust pressure by making alterations to either Q or TPR. If mean arterial blood pressure decreases, what can we do in regards to the TPR to increase it again?
if MABP decreases, we can vasoconstrict our arterioles which increases TPR and this will increase MABP again
We can adjust pressure by making alterations to either Q or TPR. If mean arterial blood pressure decreases, what can we do in regards to the flow to increase it again?
if MABP decreases, we can increase our heart rate which increases flow and this will increase MABP again
this is stimulating the baroreflex
Describe how we can get different amounts of blood in different vascular beds
It is important to distribute blood where it needs to go and the arterioles have the important role of constricting or dilating in order to control the amount of blood passing through them. If we are exercising, the skeletal muscles need more blood because they require more O2 than other places such as the digestive system. This means that there will be vasodilation of the arterioles around the skeletal muscles to increase blood flow but there will be vasoconstriction of the arterioles around the digestive system to decrease blood flow there. This is the opposite for when you are just sitting and eating.
What is the purpose of vasodilation and vasoconstriction of different vascular beds?
to alter the flow in different vascular beds but to maintain overall stable MABP
What are three control mechanisms for vascular diameter (resistance)?
neural controls
hormonal controls
local controls
Describe the extrinsic neural control of vascular diameter leading to vasoconstriction
The sympathetic nervous system releases NE onto α1-adrenergic receptors and this causes vasoconstriction
There is a normal level of sympathetic nervous activation of smooth muscles around the arterioles and if this is increased, there is vasoconstriction and if this is decreased there is vasodilation, true or false?
true
How does the number of α1-adrenergic receptors change depending on their location and why is this?
The innervation density depends on the vascular bed. In the brain, we have low numbers of α1-adrenergic receptors because there is limited need for vasoconstriction because it is important that the brain gets constant flow. In contrast, there are a high number of α1-adrenergic receptors in the skin and GI tract because there is a greater need for vasoconstriction because it is important that the flow needs to be flexible
Describe a non-cholinergic/non-adrenergic extrinsic control of vascular diameter that leads to increased blood flow
There are postganglionic nerve fibres which release NO which relaxes the smooth muscle cells and causes vasodilation and then there is decreased resistance and increased blood flow
Is the use of NO to cause vasodilation a specialised system?
How can it be affected from an external factor?
no
Viagra releases NO which has the same effect which increases blood flow to the penis to cause an erection
What three hormones can cause vasoconstriction?
adrenaline
angiotensin ||
vasopressin
What two hormones can cause vasodilation?
adrenaline
atrial natriuretic peptide
How can adrenaline cause both vasodilation and vasoconstriction?
Blood vessels have a α1-adrenergic receptor and a β2-adrenergic receptor. When adrenaline binds to the α1-adrenergic receptors it causes vasoconstriction and when it binds to the β2-adrenergic receptors, it causes vasodilation
How does the ratio of β2-adrenergic receptor: α1-adrenergic receptor change depending on the tissue/organ function? Give examples
In the skin, there is predominantly α1-adrenergic receptors because there needs to be lots of vasoconstriction whereas in the skeletal muscle, there needs to be predominantly β2-adrenergic receptors because there needs to be lots of vasodilation
Hormones that play a role in long-term regulation of MABP are also ________
vasoactive
What is the long term effect of ADH on MABP? How does it do this?
it increases cardiac output (blood volume) which leads to increased MABP
ADH increases H2O reabsorption
What is the long term effect of ADH on the vasculature?
It is also called vasopressin because it causes vasoconstriction
What is the long term effect of Angiotensin || on MABP? How does it do this?
it increases cardiac output which leads to increased MABP
Angiotensin|| increases Na+ reabsorption
What is the long term effect of ANP on MABP? How does it do this?
it decreases cardiac output (blood volume) which leads to decreased MABP
it decreases water reabsorption
What is the long term effect of Angiotensin || on the vasculature?
It is also called vasopressin because it causes vasoconstriction
What is the long term effect of ANP on the vasculature?
it causes vasodilation
What are two local/intrinsic control mechanisms of vascular diameter (ie. no nerves or hormones are involved)?
- active hyperaemia (metabolic autoregulation) which causes dilation
- flow autoregulation (myogenic autoregulation) causing both constricting or dilation
Explain how active hyperaemia works as an intrinsic control of vascular diameter
This causes blood flow changes to match changes in metabolism.
When we are exercising, the blood flow needs to go up. This means that when there is an increase in the metabolic activity in the organ, the O2 decreases (as it is being used) and there is generation of metabolites which stimulate blood vessels to dilate
Explain how flow auto-regulation works as an intrinsic control of vascular diameter
This works to control blood flow to maintain flow despite changes in perfusion pressure.
If there is poor auto-regulation, there is variable flow and the flow fluctuates over a wide pressure range.
If the auto-regulation maintains steady flow, there is similar flow over a wide range of pressures eg. if there is an increase in pressure, the smooth muscle stretches and this leads to vasoconstriction to decrease pressure.
If there is a decrease in pressure, there is reduced flow to an organ and so there is vasodilation to increase the pressure
Direct sympathetic stimulation of the systemic arterioles can cause what?
vasoconstriction by α1-adrenergic receptors
The aorta and large arteries maintain the flow of blood during diastole BECAUSE the strong elastic recoil of the arterial walls forces blood away from the heart as the aortic valve is shut
both are true and the second causes the first
