Physiology Flashcards
Define pressure
Force exerted per unit area
Define pressure gradient
The difference in forces exerted (per unit area) at either end/side of an object e.g. tube or membrane
Define flow
The volume of fluid passing a given level of the circulation/airways per unit time
Define resistance
A force that tends to oppose flow of a substance
Approximately what percentage of total blood volume is in the venous system at any one point in time?
67%
What is flow directly proportional to?
The pressure gradient
Pressure gradient = ……..x………..?
Flow x resistance
Blood pressure = ……………….x……………?
Cardiac output x systemic vascular resistance (total peripheral resistance)
At a given flow, velocity is inversely proportional to …………………..?
Cross sectional area
What type of flow is normal for vessels?
Laminar flow
What is Poiseuille’s law?
The resistance of the vessel depends on its radius, its length and the viscosity of the fluid.
8nl/pir4
Flow is direclty proportional to the fourth power of the radius of the tube - if we double the radius, flow will increase by 16 times.
Where do RBC’s tend to flow in the vessel?
Cellular components affect viscosity and thus flow; as a result of laminar flow, red cells tend to get borne along in the centre of the blood vessel (most rapid here)
What is turbulent flow?
When layers (laminae) of laminar flow break up and flow becomes disordered
Name 3 situations in which turbulent flow is more likely
- Velocity is high
- Viscosity of blood is low
- Blood vessel diameter is high
Which vessels provide the greatest resistance to flow?
Arterioles
