1.2.2 - Transport in Animals (Blood, Tissue Fluid and Lymph) Part 9 & 10

Question 1

Describe the structure of the arteries and explain why these structures are needed in order to carry out its function.

Answer 1

• Arteries have a relatively narrow lumen - to maintain pressure.
• Their walls are thick and contain collagen - to withstand pressure.
• They have elastic tissue in the walls - allows for stretching and recoiling; to withstand and maintain pressure.
• Walls contain smooth muscle - to narrow the lumen so blood can be directed to other organs.
• Inner lining of endothelium layer - to reduce friction with flowing blood.

Question 2

State the role of veins and describe how their structure helps them carry out this function.

Answer 2

• Veins carry blood back to the heart.
• Their lumen is large - for easy flow of blood.
• Their walls have thinner layers of collagen, smooth muscle and elastic tissue - they do not need to stretch / recoil / constrict blood flow.
• They contain valves - to prevent the back-flow of blood.
• Overall, they are thin - so they can be squashed.

Question 3

State the role of capillaries and describe how their structure helps them carry out their role.

Answer 3

• Capillaries allow the exchange of materials between blood and cells via tissue fluid.
• Their walls are a single layer of flattened endothelial cells - to reduce the diffusion pathway.
• Their lumen is very narrow - to ensure red blood cells are as close to the walls as possible to reduce the diffusion pathway.

Question 4

Explain, in detail, the difference between blood, tissue fluid and lymphs.

Answer 4

• Blood is the liquid held in blood vessels.
• It contains blood cells (eg. red, white and platelets) in plasma with dissolved substances.
• Tissue fluid does nor contain most the cells found in blood or plasma proteins.
• They transport oxygen to cells and carry CO₂ out.
• They are outside the blood vessels.
• Lymph **fluid **contains many lymphocytes.
• They have the same solutes as tissue fluid.
• They also have more CO₂ from the body cells and less oxygen.

Question 5

Describe how tissue fluid forms from plasma.

Answer 5

• When an artery reaches the tissues, it branches into a network of capillaries.
• The blood is under high pressure due to heart contractions.
• Plasma, with dissolved nutrients and oxygen, is forced out through the tiny gaps in the capillary wall due to hydrostatic pressure.
• The tissue fluid surrounds the cells to exchange via diffusion and facilitated diffusion.

Question 6

Describe how tissue fluid enters back into the veins.

Answer 6

• The water potential of the tissue fluid is less than the water potential in the blood.
• The hydrostatic pressure also decreases in the tissue fluid.
• This means the osmotic pressure can overcome the hydrostatic pressure.
• The fluid returns to the blood via osmosis.

Question 7

Explain why blood contains many proteins that are not found in the tissue fluid or lymph.

Answer 7

The blood plasma’s role is to serve as the protein reserve. Not all proteins are found in the tissue fluid because the tissue fluid’s role is to transport oxygen and nutrients. In addition, the plasma proteins are too big to be pushed out through the gaps of the capillary wall.