Session 5 - Blood Flow Flashcards
Define Veloicty
The rate of movement of fluid particles along the tube
What is the relationship between flow, volume and time?
Flow = Volume / Time
What is laminate flow?
The most common type of blood flow. The velocity is. Highest in the centre and there is a gradient out to the edges
What is turbulent flow?
If mean velocity increases eventually blood will become turbulent. The velocity gradient breaks down and the fluid layers begin to tumble over one another with a great increase in flow resistance
Define viscosity
Extent to which fluid layers resist sliding over one another
What will happen to velocity if viscosity increases?
The velocity will decrease
How does diameter of the tube effect velocity?
If diameter of the tube increases the middle layers of the fluid will flow faster and hence the average velocity will increase
What is relationship between flow, resistance and pressure?
Pressure = Flow x Resistance
What is the relationship between resistance and radius?
The resistance decreases with thee fourth power of the radius
How do we work out total resistance of tubes in series?
We simply sum together the resistances of each tube
How do we work out the total resistance of tubes in parallel?
1/total resistance = 1/one tubes resistance + 1/other tubes resistance
(Add 1/tube resistance for all tubes in parallel)
Which vessels of the body have the highest resistance?
Arterioles
What makes the arteries have a high pressure?
Arterioles have a high resistance which means that when the heart pumps it is difficult for the blood to pass into the Arterioles so pressure in the arteries rises.
What will happen in a distensible blood vessel if pressure decreases too low?
The wall will eventually collapse and blood flow ceases.
This happens before pressure falls to zero
What feature of vessels allow them to have capacitance?
As vessels widen, more blood transiently flows in than out
What is the systolic pressure? And what is its typical value?
The maximum arterial pressure
120mmHg
What is systolic blood pressure effected by?
- How hard the heart pumps
- Total Peripheral resistance
- Compliance of arteries
What is diastolic pressure? And what is a typical value for it?
The minimum arterial pressure
80mmHg
What is diastolic pressure affected by?
Systolic pressure
Total peripheral resistance
What is pulse pressure?
The difference between systolic and diastolic pressure
What is average pressure?
Diastolic pressure + 1/3 pulse pressure
What is the total peripheral resistance?
The sum of the resistance of all of the peripheral vasculature in the systemic circulation
What is a pulse wave?
The contraction of the ventricles generates a pulse wave which propagates along the arteries faster than the blood.
How can Arterioles act as the main resistance vessels?
Arterioles contain smooth muscle and its state of contraction determines lumen diameter and flow resistance
What is vasomotor tone?
The continuous contraction of blood vessels
Name some vasodilator metabolites?
- Hydrogen ions
- Potassium ions
- Adenosine
How does hyperaemia occur?
If circulation is cut off for a minute or two to an organ, and then blood flow returns, local vasodilator metabolites will be at a very high concentration. This means that the vessels will dilate to the maximum potential.
What is central venous pressure?
The pressure in the great veins supplying the heart
What is Venous Return?
Th rate of blood flow back to the heart. This limits cardiac output
Define Flow
The volume of fluid passing a given point per unit time
