Arteries, Veins + Capillaries

• What type of circulatory system do humans have?

  Double circulatory system
• What is the primary function of arteries?

  Carry high-pressure blood from the heart
• Why do arteries have thick muscular walls?

  To withstand high pressure of blood
• What role do elastic fibers play in arteries?

  They stretch and recoil to maintain blood flow
• What can be felt in the wrist as blood surges through arteries?

  The pulse
• What happens to blood when it passes through capillaries?

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

  Very thin walls
• Why do capillaries have thin walls?

  To allow rapid diffusion of substances
• What substances diffuse from blood to cells in capillaries?

  Glucose and oxygen
• What happens to blood after it passes through the organs?

  It returns to the heart through veins
• Why do veins have thin walls?

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

  To prevent blood from flowing backwards
• What happens to valves when blood flows in the correct direction?

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

  They close 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