L8 Flashcards
what is a very broad way of describing the arterial network structure
a multilayered system of tubes
compare and contrast arteries and arterioles
the most inner layer is the endothelial layer
arteries have lots of elastic tissue which is important for their function
arterioles have finger like smooth muscle that wraps around the lumen which gives it its function
what is the function of aorta and large arteries
Distribute blood
Pressure reservoir
- Reduce fluctuations in pressure and flow = maintain flow throughout cardiac cycle
what makes the arteries act as a pressure reservoir
The arteries and the aorta have lots of elastic tissue therefore it has the ability to change shape which is what helps it be a pressure reservoir
Some blood goes towards the periphery but some goes out which causes the arterial balloon (stretch)
what is recoil
Recoil happens during diastole. it is when the arterial walls snap back which causes the elastic potential energy to be released causing blood flow away from heart as aortic valve shut!
what happens in the aorta and large arteries during systole
Systole = stretching =
stores potential energy
what happens in the aorta and large arteries during diastole
Diastole = recoil =
release stored energy
what is compliance
the stretchiness
what does compliance =
dV / dP
what does stiffness =
1 / compliance
what happens to our arteries as we age
Young arteries are compliant
When you age you get increased smooth muscle layers, collagen and fibrous which makes it less complaint
this is also what you see in cardiovascular disease
what is the roles of the small arterioles
Main determinant of resistance (local and total peripheral resistance)
Important in controlling local flow
what is vasoconstriction and vasodilation
vasoconstriction = contraction of smooth muscle
vasodilation = relaxation of smooth muscle
how does vasoconstriction and vasodilation control the resistance of the arterioles
Smooth muscle cells wrap around the lumen.
Contraction squeezes lumen to reduce diameter
what is the min pressure just before ventricular contraction
diastolic pressure (DP)
what is the maximum arterial pressure reached during peak ventricular ejection
systolic pressure (SP)
what is the normal blood pressure
120 / 80 mmHg
systolic / diastolic
if you had hypertension what would you expect the blood pressure to be
> 140 / 90 mmHg
if you had hypotension what would you expect the blood pressure to be
< 90 / 60 mmHg
what is pulse pressure
systolic pressure - diastolic pressure
what is the calculation of mean arterial blood pressure
mean ABP = DP + 1/3(SP-DP)
diastolic pressure + 1/3 of the pulse pressure
we calc like this because the heart spends longer in diastole
what is the value for mean arterial blood pressure
90mmHg
what is the dicrotic notch
when the aortic valve closes at the end of systole. This causes a slight transient increase in pressure
why do we need to keep BP constant
for pufusion
what is mean arterial blood pressure dependent on
CO and TPR
MABP = CO x TPR
how is TPR determined
it is the sum of global resistance from all the vascular beds
how is blood pressure increase via TPR
when you had a drop in blood pressure you get vasoconstriction from SM in the arterioles
how does CO increase blood pressure
the heart increases HR which increases CO which increases BP
why is it important the BP is maintained at a homeostatic level
to maintain perfusion
describe how arterioles determine how blood flow is distributed
when specific organs need more blood then you get vasodilation of arterioles at that organ and vasoconstriction to the organs that don’t need as much blood at that time
the increase in blood flow comes from decrease in blood flow from another vascular bed
This is all designed to keep MAP at a stable level
what is important to note from changing blood flow distributions
there is no change in pressure as resistance and flow change
it is also important to know that the total volume of blood does NOT change as the increased volume of blood to one vascular bed has come from another
therefore volume to that organ changes but total volume does not
what are the control mechanisms for vascular resistance
neural controls, hormonal controls and local controls
what are the 2 ways of neural control on vascular resistance
sympathetic nervous system (noradrenalin)
postganglionic autonomic nerves
how does the sympathetic nervous system have extrinsic control over vascular resistance
the SNS releases noradrenaline which binds to the a1 adrenergic receptor
when NA is bound it causes venoconstriction
when there is less NA bound there is vasodilation
therefore there is a tonal activation of the SNS
how do we regulate how much of an effect noradrenaline has
Innervation density varies depending on vascular bed
this is because different vascular beds have different amount of the a1 adrenergic receptors
eg the brain has low numbers of α1- adrenergic receptors = limited vasoconstriction which is important because
brain needs constant flow
where as skin and GI have lots of receptors because flow needs to be flexible
how does parasympathetic have control over venous resistance
it doesn’t
how do postganglionic autonomic nerves have extrinsic control over vascular resistance
PGAN release nitric oxide which causes the relaxation of smooth muscle
this is a specialised system which is only found in specific areas of the body (GI and penis)
where does NO effect vascular resistance in the body
GI tract and penis
how does viagra work
Viagra works because it is used in the postganglionic autonomic nerve pathway, it releases NO which causes dilation to get more blood flow to the penis
what hormones cause vasoconstriction
adrenaline, angiotensin 2 and vasopressin
what hormones cause vasodilation
adrenaline, atrial natriuretic peptide
how does adrenaline cause both vasoconstriction and vasodilation
because there are 2 adrenaline receptors
a 1 adrenergic receptors = constriction
B2 = dilation
this is controlled by how many receptors are expressed
Eg skeletal muscle B2 > a1
whereas skin a1 > B2
what do ADH and angiotensin 2 do
what they usually do that effects blood
and their effect in the vasculature
they increase blood volume
ADH increases water reabsorption in the kidney which increases blood volume
angiotensin 2 causes Na+ reabsorption in the kidneys. water follows salt therefore increasing blood volume
when it acts on the vasculature it causes vasoconstriction
what does atrial natriuretic peptide do
it decreases blood volume by decreasing water reabsorption in the kidney
when it acts on the vasculature it causes vasodilation
what are the local control mechanisms
active hyperemia (metabolic autoregulation)
flow autoregulation (myogenic autoregulation)
these are the intrinsic control factors
describe what happens in active hyperemia
this happens when you are using that organ alot (eg skeletal muscles when exercising). you need more blood flow to take more O2 to make energy
the products of metabolism cause vasodilation in the vascular bed
this is a tissue specific response
where is active hyperemia highly developed
skeletal and cardiac muscle because of their high metabolic demands
what is flow autoregulation
it is the control of blood flow to maintain flow despite changes in perfusion pressure
how does flow autoregulation work
When the pressure goes up then the smooth muscle cells stretch which stimulates them to contract
Reduction in blood flow decreases the pressure reduction is stretch on the vessel stimulates them to contract
Direct sympathetic stimulation of the systemic arterioles can
cause:
A: vasoconstriction mediated by α1 adrenergic receptors
B: vasodilation mediated by α1 adrenergic receptors
C: vasoconstriction mediated by β2 adrenergic receptors
D: vasoconstriction mediated by β1 adrenergic receptors
A
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 statements are true and causal
Mean arterial blood pressure is calculated by:
A: adding diastolic and systolic pressure
B: subtracting diastolic from systolic pressure
C: adding the diastolic and systolic pressure and dividing by 2
D: adding one-third of the difference between the diastolic and systolic pressure to the diastolic pressure
D
Which of these statements is INCORRECT?
Vasopressin increases mean arterial blood pressure by:
A: increasing water absorption in the kidneys
B: decreasing stroke volume
C: causing vasoconstriction
D: increasing cardiac output
…
The flow of blood away from the heart is maintained during diastole
BECAUSE
smooth muscle cells within the
walls of the aorta constrict during diastole.
the first statement is true and the second is false
Adrenaline will increase blood flow to skeletal muscles (assuming no change in perfusion pressure)
BECAUSE
adrenaline stimulates alpha-1 adrenergic receptors in the vascular smooth muscle of skeletal arterioles to provoke
vasodilation.
a1 is constriction
therefore first is true and second is false
