L46-Peripheral resistance and blood flow

describe the properties of blood flow through a tube in terms of pressure resistance and flow using poiseuilles law

describe the flow of blood in terms of pressure

blood only flows from a region of high blood pressure to a region of low blood pressure

describe the effect of viscosity on blood flow ( how much it resists flow )

the higher the viscosity, the more resistance and the less flow

it stays constant so it doesn’t control blood flow

what is the viscocity of blood determined by

• haematocrit ( red blood cells/erythrocytes )

• it can change due to dehydration, altitude, erythropoietin

what is the effect of the radius of a blood vessel in determining resistance ( flow )

describe the total peripheral resistance

• it is the sum of the resistance of all blood vessels and determines blood pressure

• it is regulated primarily by the arterioles as this is where there’s the most resistance due to the size of their radius

describe the effect the arterioles have on blood flow to different organs

• resistance in the arterioles also determines the blood flow to individual organs

• they do this by varying the radius of the arterials which impacts how much blood can flow into the organs

what is systolic and diastolic pressure

• it is the maximum pressure after your heart has contracted/ relaxed ( usually around 120-80mm for systolic and diastolic 30-10mm )

• systolic pressure is usually measured as its difficult to measure pressure in the lungs

what is pulse

• pulse is the vibration of arteries caused by the ejection of the blood from the heart into the systemic circulation

• typical rates at rest=70 beats /min

• exercise=220beats /min

what is pulse pressure

its the difference between systolic and diastolic pressure ( 120-80=40mmHg)

what is the mean arterial pressure

• its the average pressure over the cycle

• its the commonly used measurement since diastole is usually twice as long as systole

describe the effect of height on blood pressure

• blood pressure varies when standing depending on where on the body its measured

• but height doesn’t effect blood flow???

what is hypertension

• condition caused by high blood pressure

• drugs that work against it work by relaxing the blood vessels decreasing the resistance so blood pressure is reduced

• or reduce blood volume

• its a risk factor to heart failure, kidney failure and strokes