7.6 Blood vessels and their functions

Question 1

What are the four types of blood vessels and what is their function

Answer 1

1. Arteries - carry blood away from the heart and into arterioles
2. Arterioles - smaller arteries that control blood flow from the arteries to capillaries
3. Capillaries - tiny vessels that link arterioles to veins
4. Veins - carry blood from capillaries back to the heart

Question 2

What are the components of the basic layered structure of arteries, arterioles and veins (from the outside in)

Answer 2

1. Tough fibrous outer layer - resists pressure changes from within and outside
2. Muscle layer - Contracts and so controls the flow of blood
3. Elastic layer - Helps to maintain blood pressure by recoiling
4. Endotherlium (thin inner lining) - Smooth to reduce friction and thin to allow efficient diffusion
5. Lumen - central cavity where blood flows.

Question 3

What differs between each blood vessel

Answer 3

The relative proportion of each component within the vessels physical structure

Question 4

What is the function of arteries

Answer 4

To transport blood rapidly under high pressure from the heart to the tissues

Question 5

What is the function of arterioles

Answer 5

To carry blood, under lower pressure than arteries, from the arteries to capillaries

Question 6

What is the function of veins

Answer 6

To transport blood slowly, under low pressure, from the capillaries in tissues to the heart

Question 7

How is an arteries structure related to its function

Answer 7

1. Muscle layer - Thick compared to veins. Smaller arteries can be constricted and dilated to control blood volume
2. Elastic layer - Thick compared to veins. Important that blood pressure is kept high
3. Overall thickness of the wall is great - Resists vessel bursting under pressure
4. No valves (except aorta and pulmonary artery) - Blood is under constant high pressure and doesnt tend to flow backwards

Question 8

How is an arteriole structure related to function

Answer 8

Muscle layer - thicker than arteries. Contraction of this layer allows constriction of the lumen. Controls blood flow into capillaries

Elastic layer - thinner than arteries. Blood pressure is lower

Question 9

How is a veins structure related to function

Answer 9

Muscle layer - thin compared to arteries because veins carry blood away and therefore constriction and dilation cannot change flow of blood

Elastic layer - thin compared to arteries because the low pressure of blood will not cause them to burst and pressure is too low to create recoil action

Overall thickness of the wall is small - there is no need for a thick wall because blood flow is low pressure and there is no chance of bursting.

Valves at intervals - prevents the backflow of blood because of the low pressure

Question 10

What is the function of capillarires

Answer 10

To exchange metabolic materials between the blood and the cells of the body

Question 11

What is the speed of blood flow within capillaries

Answer 11

Slow

Question 12

How does the structure of capillaries relate to their function

Answer 12

1. Their walls consist mostly of the lining layer, making them extremely thin so the diffusion distance is short
2. Numerous and highly branched, providing a large area for exchange
3. Narrow diameter and so permeate tissues, which means no cell is far form a capillary - again shortening the diffusion pathway
4. Lumen is narrow so Red Blood Cells are squeezed close to the wall - shortens diffusion pathway
5. Spaces between the lining cells - allow white blood cells to escape and deal with infections