7.6 Blood vessels and their functions

Question 1

What is the role of arteries?

Answer 1

to carry blood away from the heart into arterioles.

Question 2

what is the role of arterioles?

Answer 2

to control blood flow from arteries to capillaries

Question 3

what is the role of capillaries?

Answer 3

to link arterioles to veins, and deliver nutrients/oxygen to, and take away waster products from respiring tissues.

Question 4

what is the role of veins?

Answer 4

to carry blood from capillaries back to the heart.

Question 5

describe the basic structures of arteries, arterioles and veins.

Answer 5

consist of various layers depening on the function of the vessel, but contain the same layers which are;
tough, fibrous outer layer- resists pressure change from the inside and outside
muscle layer- contracts to control blood flow
elastic layer- helps maintain blood pressure by stretching and recoiling
thin inner lining (endothelium)- smooth to reduce friction and thin to aid diffusion
lumen- central cavity through which blood flows

Question 6

how is artery structure related to function?

Answer 6

Thicker muscle walls than veins- smaller arteries can be constricted/dilated to control the volume of blood passing through them
Thicker elastic layer- to keep blood pressure high so it can travel around the whole body. stretches at each beat of the heart and springs back when it relaxes, maintains high blood pressure.
High overall thickness- resists bursting under pressure
No valves (except leaving heart)- blood is under constant high pressure so back flow is unlikely

Question 7

How is arteriole structure related to function?

Answer 7

Thicker muscle walls than arteries- constricts the lumen, restricting blood flow and controlling movement into capillaries
Thinner elastic walls than arteries- blood pressure is lower

Question 8

how is vein structure related to function?

Answer 8

thin muscle layer- takes blood away from tissues so doesn’t need to constrict to control the flow
thin elastic layer- low pressure so vein won’t burst and too low to have recoil action
small overall thickness- no risk of bursting, allows them to flatten aiding the flow of blood
valves- prevent back flow of blood at low pressure. when muscles contract veins are compressed, raising the pressure.,valves make sure pressurised blood only flows towards the heart.

Question 9

How is capillary structure related to function?

Answer 9

walls are mostly lining layer- makes diffusion distance short for transport between blood and cells
numerous and highly branched- provides a large surface area for diffusion
narrow diameter- permeate tissues so no cell is far from diffusion pathway.
narrow lumen- red blood cells are squeezed against the walls, reducing the oxygen diffusion distance
spaces between endothelial cells- allows white blood cells to escape into tissues to deal with infection.

Question 10

What is tissue fluid?

Answer 10

• the immediate and constant environment for cells

- makes up the final journey of metabolic materials as capillaries are too small to reach every cell.

Question 11

Describe the structure of tissue fluid.

Answer 11

• contains glucose, amino acids, fatty acids, ions in solution, and oxygen. it exchanges these for waste products.
• made from blood plasma

Question 12

Describe the formation of tissue fluid.

Answer 12

• the pumping of the heart creates hydrostatic pressure at the arterial end of capillaries
• this causes tissue fluid to move out of blood plasma, but the movement is opposed by 2 forces;
  
  • hydrostatic pressure in existing tissue fluid
  • lower water potential of blood
• overall, enough pressure is created to push tissue fluid out of the blood plasma, though it is only enough to push small molecules out. this is called ultrafiltration.

Question 13

how is the tissue fluid returned to the circulatory system?

Answer 13

• it returns once it has exchanged metabolic materials with cells.
• most returns to blood plasma directly, through capillaries
• some returns through the lymphatic system

Question 14

Describe how tissue fluid is returned through the capillaries.

Answer 14

• loss of tissue fluid creates hydrostatic pressure in the capillaries
• by the time blood reaches the veinous end of the capillaries the pressure is higher outside than in
• tissue fluid is forced back into capillaries
• plasma has a lower water potential than tissue fluid so water also moves in by osmosis

Question 15

describe how tissue fluid is returned through the lymphatic system.

Answer 15

• the contents of the lymphatic system, including tissue fluid, are moved by;
  
  • hydrostatic pressure of tissue fluid
  • contraction of body muscles
• tissue fluid is then drained into veins closer to the heart.