Blood vessels and their functions

Artery structure related to function:

The muscle layer is thick compared to veins -

• This means smaller arteries can be constricted and dilated in order to control the volume of blood passing through them

The elastic layer is relatively thick compared to veins -

• Important that blood pressure in arteries is kept high if blood is to reach the extremeties of the body
• The elastic wall is stretched at each beat of the heart
• It then springs back when the heart relaxes
• This stretching and recoiling action helps to maintain high pressure and smooth pressure surges created by the beating of the heart

The overall thickness of the wall is great -

• This also resists the vessel bursting under pressure

There are no valves -

• (except in the arteries leaving the heart)
• Because blood is under constant high pressure due to the heart pumping blood into the arteries
• It therefore tends not to flow backwards

Arteriole structure related to its function:

The muscular layer is relatively thicker compared to arteries -

• The contraction of this muscle layer allows constriction of the lumen of the arteriole
• The restricts the flow of blood and so controls its movement into the capillaries that supply the tissues with blood

The elastic layer is relatively thinner than in arteries -

• Because blood pressure is lower

Vein structure related to function:

The muscle layer is relatively thin -

• Compared to arteries because veins carry blood away from the tissues and therefore the constriction and dilaton cannot control the flow of blood to tissues

The elastic layer is relatively thin -

• Compared to arteries because the low pressure of blood within the veins will not cause them to burst and pressure is too low to create a recoil action

The overall thickness of the wall is small -

• Beacause there is no need for a thick wall as the pressure within the veins is too low to create any risk of bursting
• It also allows them to be flattened easily aiding the flow of blood within them

There are valves at intervals throughout -

• To ensure that blood does not flow backwards which is might otherwise do because the pressure is so low
• When the body muscles contract, veins are compressed pressuring the blood within them
• The valves ensure that this pressure directs the blood in one direction only: towards the heart

Capillary structure related to function:

Their walls consist mostly of the…