Week 3 - Lesson 1 (Part 5) Flashcards
How is the blood flow to the body tissues and organs normally adjusted?
By changes in the degree of vasoconstriction
Where does vasoconstriction occur?
In the arterioles according to the tissues needs at a given point in time
What are the arterioles considered in the vascular tree?
Stopcocks
- principle point of resistance to blood flow in the circulatory system
Where does blood pressure take the biggest drop?
At the stopcock in the arterioles of the vascular tree
Autoregulation
Is the ability of most vascular beds to constrict in response to a rise in blood pressure and dilate in response to a fall in blood pressure
- vasoconstriction/vasodilation
What is phenomenon called of autoregulation?
Reactive hyperemia
Reactive hyperemia
Increase in blood flow which follows restoration of arterial inflow to a previously ischemic limb
What is an example of reactive hyperemia?
During exercise induced increased heart rate and vasodilation of arterioles to allow more flow to muscular branches
What happens to the diameter in vasoconstriction?
It decreases
- SVR increases
What happens to the diameter in vasodilation?
It increases
- SVR decreases
What causes high arterial pressure?
High volume of blood in the large and medium sized arteries
How is large volumes preserved?
By maintaining a balance between the amount of blood that enters and leaves the arterial tree
What is the amount of blood entering determined by?
Cardiac output
What is the amount exiting determined by? (2)
- Arterial pressure
- Total peripheral resistance
- dependant on status of microcirculation
Cardiac output
How well the heart is working
What 3 vessels are involved in microcirculation?
- Arterioles
- Capillaries
- Venules
What is the driving pressure for flow within a vessel determined by? (2)
- Potential energy
2. Kinetic energy
What is potential energy generated by?
The left ventricular contraction that distends the vessel wall
What is kinetic energy acquired by?
Flow itself
Pulsatile arteriel flowsignal
Is a summation of forward flow from the left ventricle and reverse flow from the tidal reflection
How is energy lost created?
Through friction of blood at the vessel walls and between adjacent layers of blood
Where is energy loss the highest?
In the region of stenosis due to considerable friction during turbulent flow and vortex type motion
What happens to blood within a stenosis?
An increase in blood kinetic energy associated with the increase in blood velocity
- blood is slower at the walls and faster in the centre
What is said according to Bernouilli’s principle?
There is a corresponding fall in blood pressure immediately after the stenosis
Compliance
The ability of a vessel to distend and increase volume with increasing transmural pressure
- the vessel can recoil towards its original dimensions
What does the ability of arteries and veins to stretch has a large effect on? (2)
- Perfusion
2. Blood pressure
How much larger is venous compliance compared to arteries?
30x
What is an increase in arterial stiffness due to?
Atheroma
- and is detrimental
When does atheroma occur?
Over time
- not over night
Atheroma
Plaque build up
What 2 ways can atheroma show up on US?
- Hyperechoic plaque
2. Hypoechoic plaque
Hyperechoic plaque (3)
- Calcifications
- Creates shadows
- Can cause embolisms if broken off
Hypoechoic plaque
Smooth
