Term
|
Definition
| blood flows from an area of higher pressure (the aorta) to an area of lower pressure (the vena cavae). As blood flows through the circulation system, it decreases in pressure constantly. |
|
|
Term
| Give aortic and vena cave pressure values. What does this create? |
|
Definition
A: 90mmHg
V: 0mmHg
This creates a pressure gradient, which is effectively equal to the MAP. |
|
|
Term
|
Definition
| the average blood pressure in an individual, it is the average arterial pressure during a single cardiac cycle. |
|
|
Term
Sketch the following graphs of the systemic circulation:
- vessel diameter
- total cross sectional area of vessels
- average blood pressure
- velocity of blood flow |
|
Definition
Look at notes
(make sure the lowest and highest points match the correct vessel) |
|
|
Term
|
Definition
Flow is linearly proportional to the pressure difference between two points.
DARCY -> Pride and Prejudice -> Proportional Pressure two Points |
|
|
Term
| What does Darcy's Law summarise in terms of flow? (3) |
|
Definition
1. no pressure gradient = no flow (hydrostatic conditions)
2. pressure gradient = flow from high pressure towards low (opposite direction of increasing gradient, hence negative sign)
3. the greater the pressure gradient. the greater the discharge rate |
|
|
Term
| How can the discharge rate be different, if the same pressure gradient exists? |
|
Definition
- different formation materials
- different direction |
|
|
Term
| What is the difference between fluid flow and fluid velocity? |
|
Definition
F: volume/time
V: distance/time |
|
|
Term
| What is the relationship between total cross-sectional area and mean velocity? |
|
Definition
| as total cross sectional area increases (eg capillaries) mean velocity falls |
|
|
Term
| How does total flow change in each level of the vascular system? |
|
Definition
IT DOESN'T!
it remains equal to the CO at each level of the vascular system |
|
|
Term
|
Definition
| a physical law that gives the pressure in a fluid flowing through a long cylindrical pipe |
|
|
Term
| What acts as resistance to blood flow? (3) |
|
Definition
- vessel radius
- fluid viscosity
- vessel length |
|
|
Term
| Explain why arterioles are the main site of resistance |
|
Definition
| Flow is extremely sensitive to vessel radius. A fall in radius from 1cm to 0.01cm will increase resistance by a factor of 108. |
|
|
Term
| Explain the problem with Darcy's Law and feet |
|
Definition
- MAP in the aorta is around 95mmHg
- MAP in the arteries of the foot is around 180mmHg
- Darcy's Law would predict that blood would flow from the foot to the aorta through the arteries
This does not happen. |
|
|
Term
| What does mechanical energy equal? |
|
Definition
| Pressure energy + potential energy + kinetic energy |
|
|
Term
| Why doesn't blood flow from the foot to the aorta via the arteries? |
|
Definition
- Blood in the aorta has 90mmHg potential energy
- MAP + potential energy = 185mmHg
- this is greater than the 180mmHg observed in the arteries of the feet (assuming 0 potential energy) |
|
|
Term
| How does resistance change in series? |
|
Definition
- total resistance increases if series units are added
- resistance in a series is equal to the sum of each individual componenet |
|
|
Term
| How does resistance change in parallel? |
|
Definition
- total resistance decreases if parallel units are added
- resistance in parallel is equal to the inverse sum of each individual component, so resistance gets smaller |
|
|
Term
| What are the 3 different patterns of flow in circulation? |
|
Definition
1. Laminar flow
2. Turbulent flow
3. Single-file flow |
|
|
Term
| Where does laminar flow occur? |
|
Definition
| normal arteries and veins |
|
|
Term
| Where does turbulent flow occur? |
|
Definition
| the ventricles and sometimes in the aorta |
|
|
Term
| Where does single-file flow occur? |
|
Definition
|
|
Term
|
Definition
| the liquid behaves like a series of thin concentric cells (laminae sliding past each other |
|
|
Term
| Where is the fastest/slowest flow in laminar flow? |
|
Definition
- lamina in contact with the vessel wall is helf stationary but molecule cohesive forces
- adjacent lamina slides slowly past each other, gaining velocity
- max velocity is reached at the centre of the tube |
|
|
Term
| What can lead to turbulent flow? |
|
Definition
| an atheromatous plaque once the blood has flown past the plaque |
|
|
Term
| What does Darcy's Law predict when the pressure gradient increases? |
|
Definition
| flow will increase linearly |
|
|
Term
| What point is reached in turbulence and why? |
|
Definition
flow increases only in proportion to the square root of the driving pressure: this is due to turbulence
(begins to plateau)
some pressure eneergy is dissipated as heat |
|
|
Term
| What is turbulent flow encouraged by? |
|
Definition
- high fluid velocity
- large tube diameter
- high fluid density |
|
|
Term
| What is turbulent flow discouraged by? |
|
Definition
|
|
Term
| What do these factors combine to give? |
|
Definition
|
|
Term
| What is Reynold's number? |
|
Definition
| a dimensionless quantity that is used to help predict similar flow patterns in different fluid flow situations. It is defined to be the ratio of inertial forces to viscous forces and consequently quantifies the relative importance of these two types of forces for given flow conditions. |
|
|
Term
| Where does single-file flow occur and why? |
|
Definition
- the diameter in capillaries is 6-10micrometers
- diameter of RBC = 8micrometers
- RBCs are forced into single file and deform into parachute-esque configuration (RBC's biconcave shape allows them to essentially fold) |
|
|
Term
| When is single file flow affected? |
|
Definition
| in conditions such as sickle cell anaemia : RBCs that assume an abnormal, rigid sickle cell shape. |
|
|
Term
|
Definition
| the change in volume per unit change in distending pressure |
|
|
Term
| What is compliance the reciprocal of? |
|
Definition
elastance
a measure of the tendency of a hollow organ to recoil towards its original dimensions upon removal of a distending or compressing force |
|
|
Term
| Do veins or arteries possess high compliance? |
|
Definition
| Veins due to their thin walls and ability to be stretched. They can accommodate large increases in blood volume in response to a small increase in blood pressure. |
|
|
Term
Veins are _____ reservoirs.
Arteries are _____ reservoirs. |
|
Definition
Veins are volume reservoirs.
Arteries are pressure reservoirs. |
|
|
Term
| Define distending pressure |
|
Definition
| The distending pressure acting on a vessel is the pressure inside minus the pressure outside (i.e. the transmural pressure) |
|
|
Term
| How is the distending pressure balanced? |
|
Definition
by forces within the vessel wall (tension, T) otherwise it will rupture.
the magnitude of tension in the wall necessary to withstand the transmural pressure is influenced by both the vessel radius and the wall thickness. |
|
|
Term
| What is the Law of LaPlace? |
|
Definition
| the relationship between the forces in the blood vessel wall |
|
|
Term
| Explain why walls need to be thick in large arteries |
|
Definition
| the transmural pressure and radius are large |
|
|
Term
| Explain why walls are thin in capillaries in capillaries |
|
Definition
| the transmural pressure is quite low and the radius is very small |
|
|
Term
| Where is vessel rupture most likely? |
|
Definition
in elastic arteries
aortic rupture is relatively common and fatal medical event |
|
|
