0506 - Blood Flow RM Flashcards
Be cognisant of a few physical principles that relate flow, pressure, and velocity, among them Ohm’s law. Realise that arteries are cardiofugal and veins cardiopetal vessels. Know the notion of blood pressure Appreciate factors determining resistance, pressure, flow, and its characteristics Understand the distal impact of a resistance change Recognise why some vascular beds display different characteristics
How are pressure, flow, and velocity related?
Three components of flow, if you alter one, then it will have an effect on the other two. Ohm’s law sums up relationship P=RF (pressure=resistanceflow). In medicine, this is given as MAP=TPRCO (Mean Arterial Pressure = Total Peripheral Resistance * Cardiac Output).
How is pressure calculated?
P=Force/area (=energy/volume).
What is the flow difference between veins and arteries?
Veins = cardiopetal (take blood to heart), low pressure (7torr), take blood from capillaries.
Arteries = cardiofugal (take blood from heart), high pressure (95torr), take blood to capillaries.
Either veins or arteries can carry oxygenated or deoxygenated blood – depending on whether they are in systemic or pulmonary circulation
What is the role of blood circulation?
Continuous flow of blood through all tissues to allow for transport of: • O2 and CO2 • Nutrients and metabolites • Water, electrolytes and buffers • Cells • Proteins • Hormones • Heat (dissipation)
Is blood flow constant through the body?
No, but NET flow is constant as cardiac output must always equal venous return. Pressure and velocity are not constant, and it is the change of pressure that allows blood to flow.
What is the effect of the capillary beds on blood flow and blood pressure?
Velocity slows in each individual capillary, however due to the sheer number of capillaries total flow remains constant. The massive resistance imposed by arterioles and capillaries significantly drops blood pressure on the venous return side.
Which vessels have the greatest impact on blood pressure? How do they do this?
Arterioles (pre-capillary). They have significant total cross-sectional area (i.e. blood is spread through several), as well as the capacity to dilate or constrict, thereby changing the peripheral resistance and blood pressure.
Which blood vessels have the largest wall tension?
Arteries – the bigger the artery, the more wall tension – they are built as they are to withstand significant wall tension and control the distal flow.
What is Ohm’s Law for circulation (key concept)
MAP = TPR x CO
Mean Arterial Pressure = Total Peripheral Resistance x Cardiac Output
