The Circulatory System

Question 1

What order do the blood vessels go in?

Answer 1

Arteries, smaller arteries ,arterioles which branch into capillary beds, into venules and then into veins.

Question 2

Why does blood pressure and the rate of flow decrease along the circulatory system?

Answer 2

Arteries carry blood at high pressure very rapidly and as it flows into arterioles and then the capillary beds, resistance to the flow of blood increases causing blood pressure and rate of flow to fall. Blood flows back into the venules and veins and back to the heart under low pressure, as blood flows in the direction of decreasing pressure.

Question 3

Explain the qualities/ roles of arteries

Answer 3

arteries

• Carry blood away from the heart at high blood pressure
• Have a thicker wall and a smaller lumen than veins and contain more elastic fibres.
• Do not possess valves except for the aorta and pulmonary artery,
• Carry oxygenated blood except for pulmonary artery

Question 4

Explain the role of the aorta

Answer 4

-Aorta has a lot of elastic tissue and when the left ventricle contracts, the aorta stretches and retains some of the blood forced out the ventricle. When the ventricle relaxes, the artery wall recoils and forces blood to the body tissues. Helps provide a smooth flow of blood and maintain a high pressure.

Question 5

Why do arteries near the heart contain a higher ratio of elastic fibres to smooth muscle fibres?

Answer 5

To withstand the high blood pressure and help smooth out blood flow.

Question 6

What is the role of arterioles?

Answer 6

Arterioles don’t have to withstand the high pressure and thus have more smooth muscle fibres. They can control the flow of blood to different tissues/ organs by contraction/ relaxation of their smooth muscle wall.

Question 7

What is the role of the veins and the qualities?

Answer 7

Carry blood under low pressure to the heart
Thinner walls than arteries and contain less elastic fibres/ smooth muscle.
Carry deoxygenated blood apart from pulmonary vein
Lumen is larger than arteries so even at low pressure, blood flows back to the heart at same rate it left.
Contracting muscles in the legs and body press on the veins and squeeze the blood along the lower back where the pressure from the heart isn’t enough.
Semi-lunar valves which prevent back-flow.

Question 8

What is the role of capillaries?

Answer 8

• Form the connection between the arteries that carry blood away from the heart and the veins that return blood to the heart.
• Walls are one cell thick and cells aren’t far away, giving a short diffusion pathways. Gaps between the endothelial cells increase permeability.
• Numerous and highly branched giving large SA
• Cross-section is high producing a large frictional resistance, reducing the rate of blood flow and allowing more time for substance exchange.
• Very small diameter and red blood cells are squeezed flat against the wall, reducing O2 diffusion distance.