[7.6] (1/2) blood vessels and their functions

Question 1

what is the function of arteries?

Answer 1

to carry blood away from the heart into arterioles

Question 2

what is the function of arterioles?

Answer 2

smaller arteries that control blood flow from arteries to capillaries

Question 3

what is the function of capillaries?

Answer 3

to link arterioles to veins

Question 4

what is the function of veins?

Answer 4

to carry blood from the capillaries back to the heart

Question 5

how is artery structure related to function?

Answer 5

• muscle layer is thicker than in veins
• elastic layer is thicker than in veins
• overall thickness of wall is great
• no valves

Question 6

why do arteries have a thicker muscle layer (than veins)?

Answer 6

smaller arteries can be constricted and dilated to control volume of blood passing through them

Question 7

why do arteries have a thicker elastic layer (than veins)?

Answer 7

• it is important that blood pressure in arteries is kept high so blood can reach extremities of the body
• elastic wall is stretched at each beat of the heart (systole) and springs back when heart relaxes (diastole)
• this stretching and recoil action helps to maintain high pressure and smooth pressure surges created by the beating of the heart

Question 8

why do arteries have an overall thick wall?

Answer 8

overall thickness of the wall is great because this resists the vessel bursting under pressure

Question 9

why do arteries not have valves?

Answer 9

• blood is under constant high pressure due to heart pumping blood into arteries so tends not to flow backwards
• only has valves in arteries leaving the heart

Question 10

how is arteriole structure related to function?

Answer 10

• muscle layer is thicker than in arteries
• elastic layer is thinner than in arteries

Question 11

why do arterioles have a thicker muscle layer (than arteries)?

Answer 11

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

Question 12

why do arterioles have a thinner elastic layer (than arteries)?

Answer 12

because blood pressure is lower

Question 13

how is vein structure related to function?

Answer 13

• muscle layer is thinner than in arteries
• elastic layer is thinner than in arteries
• overall thickness of wall is small
• valves at intervals throughout

Question 14

why do veins have a thinner muscle layer (than arteries)?

Answer 14

• veins carry blood away from tissues (towards heart)
• their constriction and dilation cannot control the flow of blood to the tissues

Question 15

why do veins have a thinner elastic layer (than arteries)?

Answer 15

low pressure of blood in veins will not cause them to burst and pressure is too low to create a recoil action

Question 16

why do veins have an overall thin wall?

Answer 16

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

Question 17

why do veins have valves at intervals throughout?

Answer 17

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

Question 18

how is capillary structure related to function?

Answer 18

• walls consist mostly on the lining layer
• numerous and highly branched
• narrow diameter
• lumen is narrow
• spaces between the lining (endothelial cells)

Question 19

why do capillary walls consist mostly of the lining layer?

Answer 19

• makes them extremely thin, so there is a short diffusion distance
• this allows for rapid diffusion of materials between the blood and cells

Question 20

why are capillaries numerous and highly branched?

Answer 20

provides a larger cumulative surface area for exchange

Question 21

why do capillaries have a narrow diameter?

Answer 21

permeates tissues; no cell is far away from a capillary and there is a short diffusion pathway

Question 22

why do capillaries have a narrow lumen?

Answer 22

• red blood cells are squeezed flat against the side of a capillary
• this brings them even closer to the cells to which they supply oxygen
• again, this reduces the diffusion distance

Question 23

why do capillaries have spaces between the lining (endothelial cells)?

Answer 23

allows white blood cells to escape in order to deal with infections within tissues