blood vessels

• What is the function of the double circulatory system in humans?

  It pumps blood from the heart to the lungs
• What happens to blood after it collects oxygen in the lungs?

  It returns to the heart and is pumped around the body
• What do arteries carry from the heart?

  Very high pressure blood
• Why do arteries have thick muscular walls?

  To withstand the very high pressure of blood
• What is the role of elastic fibers in arteries?

  They stretch and recoil to keep blood moving
• What can be felt in the wrist as a pulse?

  The surge of blood through arteries
• What happens to blood when it flows through capillaries?

  Substances diffuse between blood and cells
• What is the structure of capillaries?

  They have very thin walls
• Why do capillaries have thin walls?

  To allow rapid diffusion of substances
• What happens to blood after it passes through the organs?

  It makes its way back to the heart
• Why do veins have thin walls?

  Because the blood pressure is low
• What is the function of valves in veins?

  To stop blood from flowing backwards
• How do valves in veins operate when blood flows correctly?

  They open to allow blood to flow through
• What happens to valves when blood starts to flow backwards?

  They shut to prevent backflow
• How do the structures of arteries, veins, and capillaries relate to their functions?

  • Arteries: Thick muscular walls withstand high pressure
  • Veins: Thin walls and valves prevent backflow
  • Capillaries: Thin walls allow rapid diffusion of substances
• What are the main components of the human circulatory system?

  • Heart
  • Arteries
  • Veins
  • Capillaries