Blood Vessels

Question 1

What are blood vessels?

Answer 1

Materials are transported around the body by the blood which is confined within blood vessels. There are different types of them, arteries, arterioles, capillaries and veins.

Question 2

Arteries?

Answer 2

Carry blood away from the heart and into arterioles.

Question 3

Arterioles?

Answer 3

Smaller arteries that control blood flow from arteries to capillaries.

Question 4

Capillaries?

Answer 4

Tiny vessels which link arterioles to veins.

Question 5

Veins?

Answer 5

Carry blood from capillaries back to the heart.

Question 6

Arteries, arterioles and veins all have the same basic layered structure from the outside in?

Answer 6

• tough fibrous outer layer that resists pressure changes from both within and outside.
• thin inner layer (endothelium) that is smooth to reduce friction and thin to allow diffusion.
• elastic layer that helps maintain blood pressure by stretching and springing back.
• muscle layer that can contract and so controls the flow of blood.
• lumen which is not a layer but the central cavity of the blood vessel which blood flows through.

Question 7

What differs between the structure of arteries and arterioles?

Answer 7

The relative proportions of each layer.

Question 8

Artery structure related to function?

Answer 8

The function of arteries is to transport blood rapidly under high pressure from the heart to the tissues.

• 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 though.
• the elastic layer is relatively think compared to the veins. It’s important that blood pressure is kept high so blood can reach the extremities of the body. The elastic wall is stretched at each heart beat it then springs back when the heart is relaxed this helps to maintain high pressure and smooth pressure surges when the heart beats.
• the overall thickness of the wall is great, this resists the vessel bursting under pressure.
• there are no valves, the blood is under constant high pressure due to the heart pumping blood into the arteries so tends not to flow backwards.

Question 9

Arterioles structure to function?

Answer 9

• the elastic layer is relatively thinner than in arteries so the blood pressure is lower.
• the muscle layer is relatively thicker in the arteries. The contraction of this muscle layer allows constriction if the lumen of the arterioles. This restricts the flow of blood and so controls its movements into the capillaries that supply the tissues with blood.
• arterioles carry blood under lower pressure than the arteries from arterioles to capillaries. They also control the flow of blood between the two.

Question 10

Vein structure related to function?

Answer 10

Veins transport blood slowly under low pressure from the capillaries in tissues to the heart.

• the muscle layer is relatively thin, the veins carry blood away from the tissues and therefore their constriction and dilation can’t control the flow of blood to tissues.
• the elastic layer is relatively thin, the low pressure of the blood within the veins will not cause them to burst and the pressure is too low to create a recoil action.
• the overall thickness of the wall is small, there is no need for a thick wall as the pressure is too low to create any risk of bursting. It also allows the, to be flattened easily aiding the flow of blood within them.
• there are valves at intervals throughout to ensure that blood doesn’t flow backwards as it may due to the low pressure. When muscle contract veins are compressed which pressurises the blood within them. The valves ensure that this pressure directs the blood in one direction towards the heart.