Factors Effecting Blood Flow Flashcards
Define flow
Volume of fluid passing a given point per unit time
Define velocity
Rate if movement of fluid particles along the tube
What drives flow through blood vessel?
The gradient of pressure
At a given flow what is velocity inversely proportional to?
Cross sectional area.
Will velocity be low or high with a small cross sectional area?
Extra point - give an example in the body
Small cross sectional area means a high velocity.
Extra point - aort
Will velocity be low or high with a large cross sectional area?
Extra point - give an example in the body
With a large cross sectional area velocity will be low.
Extra point - capillaries
What is directly proportional to cross sectional area?
Mean velocity
Compare flow and velocity in a vessel.
Flow is consistent, velocity can vary along the length of the vessel.
Name 2 types of flow
Laminar and turbulent
What is laminar flow?
Extra point - what noise does it make?
Flows nicely. Like this in most blood vessels. The fluid layers flow over one another.
Extra point - it doesn’t make a noise
What is the velocity pattern in a laminar flow vessel?
The gradient of velocity is from the middle to the edge of the vessels. It is highest in the middle and lowest at the edge.
What is turbulent flow?
Extra point - what noise does it make?
The velocity and flow are above a threshold. The velocity gradient breaks down and velocity is constantly changing as the fluid tumbles. Cn cause vessel wall damage.
Extra point - it makes a whooshing noise.
What type of resistance increases with turbulent flow?
Flow resistance. This means it is harder to pump turbulent blood.
In a vessel of constant flow, what determines mean velocity?
The viscosity of the fluid and the radius of the vessel.
What is viscosity?
The extent to which fluid layers resist sliding over one another within a vessel.
What does high viscosity cause?
Slows the central layers flowing and reduces the average velocity.
What is mean velocity inversely proportional to?
Viscosity
What is flow a product of?
Mean velocity and cross sectional area.
Poiseulles law can only be used for one type of flow, which one is it?
Laminar flow only.
If blood vessels are connected in series, does the resistance increase or decrease?
Increase.
If blood vessels are connected in parallel, does the resistance increase or decrease?
Decrease.
If flow is fixed what will happen with higher resistance?
Greater pressure change from one end of the vessel to the other.
If flow is fixed what does a bigger tube cause?
The flow to be slower.
If pressure if fixed what does a bigger tube cause?
A bigger flow.
What vessels have low resistance in the cardiovascular system?
Arteries, capillaries in parallel and venules/veins
What vessels have high resistance in the cardiovascular system?
Arterioles and individual capillaries.
What are some examples of issues with blood flow within the cardiovascular system?
Turbulent flow - increases resistance.
Vessels are not fixed - they have distensible walls which stretch due to transmural pressure.
How does pressure effect blood flow within distensible vessels?
High pressure makes the resistance fall so its easier for blood to flow. If the pressure falls too much, the walls collapse and blood flow stops.
What is the most distensible vessel in the cardiovascular system?
Veins.
What is capacitance?
Extra point - how does it work?
The ability to store blood in vessels.
Extra point - the walls stretch with increasing pressure, so more blood flow enters than leaves the vessel. It gets stored at the edges of the vessel.
