Blood vessels - Capillaries + veins

Question 1

What is the role of capillaries?

Answer 1

They link arterioles + venules, forming extensive network through all tissues in body + are main site of diffusion

Question 2

Describe the capillary structure:

Answer 2

• Lumen very small + RBCs travel in single file
• Substances exchanged through capillary walls inbetween tissue cells + blood
• Gaps between endothelial cells that make up capillary walls are large

Question 3

What is the type of blood going through capillary beds?

Answer 3

Blood entering is oxygenated and blood leaving is deoxygenated

Exceptions to this are in lungs + placenta

Question 4

How are capillaries adapted to their role in exchange?

Answer 4

• Provide very large SA for diffusion of substances in + out
• Total cross sectional area of capillary greater than arteriole supplying them so rate of blood flow falls
• Slow movement of blood gives more time for diffusion
• Walls are single endothelial cells thick, giving thin layer for diffusion

Question 5

What type of blood do veins carry + in what direction?

Answer 5

Carry deoxygenated blood from body cells to heart

Question 6

What are the exceptions to veins?

Answer 6

Pulmonary vein = Carries deoxygenated blood from lungs to heart

Umbilical vein = Carries deoxygenated blood from placenta to fetus

Question 7

Explain vein structure:

Answer 7

• Dont have pulse, but hold large amount of blood
• Blood pressure very low
• Medium-sized veins have valves to prevent backflow of blood
• Walls contain lots of collagen + little elastic fibre
• Vessels have wide lumen + smooth lining so blood flows easily

Question 8

What is the difference between veins + venules?

Answer 8

Blood flows from capillaries into venules, which join together to make veins

Question 9

How are veins adapted to transport blood under low pressure + moving against gravity?

Answer 9

• One way valves at intervals = Flaps/infoldings of inner lining of vein, blood flows towards heart + valves open, backflow means valves close
• Veins run through active muscles = Muscles contract, squeeze veins, forces blood to heart
• Breathing movements of chest act as pump = Pressure changes + squeezing actions move blood in veins

Question 10

How do valves help when muscles relax?

Answer 10

Prevents backflow