3.2.3 Blood Vessels

Question 1

Structure of Arterioles

Answer 1

• Muscular so can contract to partially cut off blood flow to capillaries
• Eg to gut during exercise

Question 1

Structure of Veins

Answer 1

• Valves prevent backflow
• No need for thick muscular layer because veins don’t need to withstand high BP
• Lumen larger (Low blood pressure, lots of blood pumped, less friction between blood and endothelial layer)
• Thin muscle
• No pulse

Question 2

Structure of Arteries

Answer 2

Layers :
1. Endothelial layer (reduces friction for free blood flow)
2. Smooth muscle cells and thick elastic tissue (thick muscle cells allow arteries to withstand high pressures, can contract and narrow lumen for reduced blood flow) (Elastic tissue helps maintain blood pressure, stretches and recoils to even out fluctuations in pressure)
3. Collagen layer (prevents vessels from overstretching)
.
Arteries have a narrow lumen to help maintain high BP. Pulse present.

Question 3

Structure of Venules

Answer 3

• Connect capillaries to veins
• Large lumen, few / no elastic fibres
• Blood is low pressure after passing through capillaries, so no need for muscular layer

Question 4

Capillaries Function and Structure

Answer 4

• Thin walls
• Leaky, allowing substances to leave blood to reach body tissues
• Form networks called capillary beds (exchange sites)

Structure
- Endothelium is 1 cell thick
- Walls have pores allowing blood plasma to leak out to form TISSUE FLUID