Blood Vessels

What are the three main types of blood vessels?

1. Arteries
2. Veins
3. Capillaries

How are arteries adapted to carry blood under high pressure?

• Walls are thick and muscular to withstand pressure.
• Contain elastic fibers that allow them to stretch and spring back.
• Have a relatively narrow lumen to maintain high pressure.

What is the function and structure of capillaries?

• Function: Exchange of substances (e.g., O_{2}, glucose) between blood and tissues.
• Adaptations:
  • Walls are only one cell thick, providing a short diffusion pathway.
  • Permeable walls allow substances to diffuse in and out.

How are veins adapted to return blood to the heart?

• Have a wide lumen to help blood flow despite low pressure.
• Walls are thinner than artery walls.
• Contain valves to prevent the backflow of blood.

Why do veins have valves but arteries do not?

Blood in veins is at a much lower pressure than in arteries, so valves are necessary to ensure blood flows in one direction (towards the heart) and does not flow backwards.

How do you calculate the rate of blood flow?

The rate of blood flow is calculated using the formula:
\text{Rate of blood flow} = \frac{\text{volume of blood}}{\text{number of minutes}}