7.6 - Blood vessels and their functions

Question 1

what are the 4 different types of blood vessels

Answer 1

• Arteries
• Arterioles
• capillaries
• Veins

Question 2

what is the function of the arteries

Answer 2

Carry blood away from the heart and into the arterioles

Question 3

what is the function of the arterioles

Answer 3

are smaller arteries that control blood flow from arteries to capillaries

Question 4

what is the function of the capillaries

Answer 4

tiny vessels that link arterioles to veins

Question 5

what is the function of the veins

Answer 5

carry blood from capillaries back to the heart

Question 6

do all the blood vessels have the same structure

Answer 6

• no
• however they all have the same basic layered structured from outside inwards

Question 7

describe the basic layered structure of all the blood vessels

Answer 7

• tough fibrous outer layer: resists pressure changes from within and outside
• muscle layer: contracts to control the flow of blood
• elastic layer: helps to maintain blood pressure by stretching and springing back (recoiling)
• Thin inner lining (endothelium): which is smooth to reduce friction and thin to allow diffusion
• Lumen: central cavity of the blood vessel through which blood flows

Question 8

draw a diagram of an artery, vein and capillary. Make sure to include labels of the individual layers

Answer 8

Question 9

why do arteries need to be adapted to their function

Answer 9

• they have to transport blood rapidly under high pressure from the heart to the tissues

Question 10

what are some of the artery’s adaptations for its functions

Answer 10

• thick muscle layer (compared to veins)
• thick elastic layer (compared to veins)
• greater overall thickness of wall
• no valves

Question 11

describe how the adaptation of a ‘thick muscle layer’ is related to the artery’s function

Answer 11

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

Question 12

describe how the adaptation of a ‘thick elastic layer’ is related to the artery’s function

Answer 12

• because it’s crucial that blood pressure = high in the arteries so that blood can reach all around the body
• the elastic wall can be stretched during systole
• and then spring back during diastole
• this stretching and recoil action helps to maintain high pressure and smooth pressure surges created by the beating of the heart

Question 13

describe how the adaptation of a ‘greater overall thickness of wall’ is related to the artery’s function

Answer 13

to resist the vessel bursting under pressure

Question 14

describe how the adaptation of ‘no valves’ is related to the artery’s function

Answer 14

(except in the arteries leaving the heart)
- because blood is under constant high pressure due to the heart pumping blood into the arteries
- it doesn’t tend to flow backwards, and there’s no need for a valve to prevent backflow

Question 15

why do arterioles need to be adapted for their function

Answer 15

• they carry blood under lower pressure than the arteries, from the arteries –> capillaries
• they also control the flow of blood between the 2

Question 16

what are some of the Arteriole’s adaptations of the for its functions

Answer 16

• thicker muscular layer (than in the arteries)
• thinner elastic layer (than in the arteries)

Question 17

describe how the adaptation of a ‘Thicker muscular layer’ is related to the arteriole’s function

Answer 17

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

Question 18

describe how the adaptation of a ‘thinner elastic layer’ is related to the arteriole’s function

Answer 18

because blood pressure is lower

Question 19

why do the veins need to adapted for their function

Answer 19

• veins need to transport blood slowly, under low pressure
• from the capillaries in tissues to the heart

Question 20

what are some of the vein’s adaptations for its functions

Answer 20

• thin muscular layer (compared to arteries)
• thin elastic layer (compared to arteries)
• overall thickness of the wall is small
• the are valves at intervals throughout

Question 21

describe how the adaptation of ‘thin muscular layer’ relates to the function of the veins

Answer 21

• because the veins carry blood away from the tissues and therefore their constriction and dilation can’t control the flow of blood to the tissues

Question 22

describe how the adaptation of a ‘thin elastic layer’ relates to the function of the veins

Answer 22

• because the low pressure of blood will not cause them to burst and pressure is too low to cause a recoil action

Question 23

describe how the adaptation of a ‘smaller overall thickness of the wall’ relates to the function of the veins

Answer 23

• there’s no need for a thick wall as the pressure in the veins won’t cause them to burst
• pressure is too low to create a recoil action

Question 24

describe how the adaptation of a ‘having valves at intervals throughout’ relates to the function of the veins

Answer 24

• ensures that blood doesn’t flow backwards, which it might otherwise do because the blood pressure is so low
• when body muscles contract, veins are compressed, pressurising the blood within them
• the valves ensure that this pressure directs the blood in 1 direction only (to the heart)

Question 25

why do capillaries need to adapted for its function

Answer 25

• they need to exchange metabolic materials such as oxygen, carbon dioxide and glucose between the blood and the cells of the body
• blood flow is slow

Question 26

what are some of the adaptations of the capillaries for its functions

Answer 26

• the walls consist mostly of the lining layer
• they are numerous and highly branched
• narrow diameter
• lumen in narrow
• spaces between the lining (endothelial) cells

Question 27

describe how the adaptation of a ‘wall consisting mostly of the lining layer’ is related to the capillary’s functions

Answer 27

• makes them extremely thin, creates a short diffusion pathway
• allowing for rapid diffusion of materials between the blood and the cells

Question 28

describe how the adaptation of ‘numerous and highly branched’ is related to the capillary’s functions

Answer 28

provides a large SA for exchange

Question 29

describe how the adaptation of ‘narrow diameter’ is related to the capillary’s function

Answer 29

• to permeate tissues, which means that no cells is far from a capillary and there is a short diffusion pathway

Question 30

describe how the adaptation of ‘narrow lumen’ is related to the capillary’s function

Answer 30

• so red blood cells are squeezed flat against the side of the capillary
• bringing them even closer to the cells that they supply oxygen to
• reducing the diffusion distance

Question 31

describe how the adaptation of ‘spaces between the lining (endothelial) cells’ is related to the capillary’s function

Answer 31

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

Question 32

what are all the molecules that tissue fluid contains, why does it contain them?

Answer 32

it is a watery liquid that contains:
- glucose
- amino acids
- fatty acids
- ions in solution
- oxygen
—-> to supply tissues with these substances

Question 33

what is tissue fluid formed from

Answer 33

formed from blood plasma

Question 34

describe how tissue fluid is pushed out the capillaries

Answer 34

• How much liquid leaves the plasma to form tissue fluid depends on two opposing forces:
  1) When blood is at the arterial end of a capillary, the hydrostatic pressure is great enough to push molecules out of the capillary
  2) Proteins remain in the blood; the increased protein content creates a water potential between the capillary and the tissue fluid
• However, overall movement of water is out from the capillaries into the tissue fluid
• At the venous end of the capillary, less fluid is pushed out of the capillary as pressure within the capillary is reduced
• The water potential gradient between the capillary and the tissue fluid remains the same as at the arterial end, so water begins to flow back into the capillary from the tissue fluid
• Overall, more fluid leaves the capillary than returns, leaving tissue fluid behind to bathe cells

Question 35

describe the result of the pressure pushing tissue fluid out the capillaries

Answer 35

• the pressure is only enough to force small molecules out of the capillaries, leaving all cells and proteins in the blood because these are too large to cross the membranes
• this type of filtration under pressure is called ultrafiltration

Question 36

what happens once tissue fluid has exchanged metabolic materials with the cells it bathes

Answer 36

• it’s returned to the circulatory system
• most tissue fluid returns to the blood plasma directly via the capillaries

Question 37

describe the process by how tissue fluid returns to the blood plasma via the capillaries

Answer 37

• the loss of tissue fluid from the capillaries reduces the hydrostatic pressure inside them
• as a result, by the time the blood has reached the venous end of the capillary network its hydrostatic pressure is usually lower than that of the tissue fluid outside it
• therefore tissue fluid is forced back into the capillaries by this gradient
• in addition, the plasma has lost water and still contains proteins. It therefore has a lower water potential than the tissue fluid
• As a result, water leaves the tissue by osmosis down a water potential gradient

Question 38

does all tissue fluid get returned to the capillaries

Answer 38

• no
• the remainder is carried back via the lymph capillaries in the form of lymph

Question 39

describe the lymph capillaries

Answer 39

• The lymph capillaries are separate from the circulatory system
• They have closed ends and large pores that allow large molecules to pass through
• The lymph eventually reenters the bloodstream through lymph capillaries —> veins located close to the heart

Question 40

describe how contents of lymph are formed

Answer 40

• Larger molecules that are not able to pass through the capillary wall enter the lymphatic system as lymph
• Small valves in the vessel walls are the entry point to the lymphatic system
• The liquid moves along the larger vessels of this system by compression caused by body movement. Any backflow is prevented by valves

Question 41

Why is it important that any plasma proteins that have escaped from the blood are returned to the blood via the lymph capillaries

Answer 41

If plasma proteins were not removed from tissue fluid they could lower the water potential (of the tissue fluid) and prevent the reabsorption of water into the blood in the capillaries

Question 42

If blood pressure is high (hypertension) then what does this mean for the pressure at the arterial end

Answer 42

• the pressure at the arterial end is even greater
• This pushes more fluid out of the capillary and fluid begins to accumulate around the tissues. This is called oedema