CVS- Blood Flow Flashcards
What is the definition of velocity?
The rate of movement of fluid particles along the tube
What is the definition of blood flow?
The volume of fluid passing a given point per unit time
What is the relationship between pressure and flow?
Flow is proportional to the pressure difference between the ends of a vessel
What is laminar flow?
When flow is straight and fastest in the centre
What is turbulent flow?
As mean velocity increases layers of fluid try to move over each other
What is viscosity?
The extent to which fluid layers resist sliding over each other
What is the relationship between velocity and cross sectional area?
At given flow velocity is inversely proportional to cross sectional area.
However at a constant velocity gradient - velocity is proportional to cross sectional area
What is the relationship between resistance and pressure at fixed flow?
The higher the resistance the greater the pressure change from one end to the other
What is the relationship between flow and resistance at fixed pressure?
The higher the resistance the lower the flow (at fixed pressure)
Why are capillaries lower resistance than arteries?
The capillaries are in parallel so have a high combined cross sectional area so have a low resistance.
Which vessels are high resistance?
Arterioles - these aim to control circulation
Why do arteries have high pressure?
The high resistance of the arterioles means it is difficult to push blood into them - so pressure increases
What causes turbulent flow?
Can occur in some vessels = Aorta at high flow
If a vessel is narrowed e.g atherosclerosis
Heart as a bruit
What vessel shows most distensibility?
The veins
Why do the walls of distensible vessels collapse at low pressure?
Because the lumen isn’t wide enough to remain open
What is total peripheral resistance?
The total opposed blood flow resistance in the systemic circulation
What does the systolic blood pressure show?
This is the maximum arterial pressure (during systole)
Affected by the hearts ability to pump blood
The total peripheral resistance
And the compliance of arteries (ability to stretch)
Why isn’t the diastolic pressure 0?
Because the artery walls are distensible and arteries recoil after systole and flow continues through the arterioles
What is the diastolic pressure affected by?
The systolic pressure
Total peripheral resistance
What is pulse pressure?
The difference between systolic and diastolic pressure
How is average pressure calculated?
Diastolic + 1/3 PP
How is blood flow controlled in skeletal muscle and why?
By pre capillary sphincters
Because blood flow change happens regularly
What is the central venous pressure?
The pressure in the great veins which fills the heart in diastole
