Relationship Between Blood Pressure And Blood Flow

Question 1

Structure and function of blood vessels

Answer 1

1. Arteries are thick elasticated vessels with thick walls, carrying blood away from the heart under high pressure
2. Arterioles are muscular but thinner than arteries and deliver oxygenated blood to tissues
3. Capillaries are very thin, fenestrated, high surface area vessels that exchange materials with cells
4. Veins carry blood towards the heart, are very thin and contain valves for function at low pressure

Question 2

What causes blood to flow

Answer 2

1. Mean arterial pressure (MAP) drives blood flow
2. Blood pressure is the force exerted by blood against vessel wall
3. Blood flow proportional to pressure gradient, from high blood pressure to low blood pressure, and inversely proportionate to vascular resistance, the opposition to blood flow by blood vessels
4. Flow = delta P / R

Question 3

Describe the influence of total peripheral resistance on mean arterial pressure

Answer 3

1. MAP = deltaP
2. Blood flow = Cardiac output
3. Since blood flow = delta P / R
4. CO = MAP / TPR
5. MAP = CO x TPR

Question 4

Explain starling’s forces that govern the movement of fluid across capillary wall

Answer 4

There are four main starling’s forces in capillary fluid exchange with cells
1. Capillary hydrostatic pressure = pressure exerted by blood against capillary wall. Pushes materials into interstitial fluid and is higher at the arteriolar end than venular
2. Interstitial fluid hydrostatic pressure = pressure exerted by interstitial fluid against capillary. Pushes materials into capillary. Most of the time is low and negligible
3. Colloid osmotic pressure = pressure exerted by proteins within capillary, drawing fluid into the capillary
4. Osmotic pressure of interstitial fluid = pressure exerted by solutes drawing materials out of capillary

Net exchange pressure = outward pressure - inward pressure
= (capillary hydrostatic pressure + osmotic pressure of interstitial fluid) - (colloid osmotic pressure + interstitial fluid hydrostatic pressure)