arteries, veins and capillaries

• What type of circulatory system do humans have?

  Double circulatory system
• Where does blood collect oxygen in the circulatory process?

  In the lungs
• What happens to blood after it collects oxygen in the lungs?

  It returns to the heart
• What is the primary function of arteries?

  Carry high-pressure blood from the heart
• What is the first adaptation of arteries mentioned?

  Very thick muscular walls
• Why do arteries have thick muscular walls?

  To withstand high pressure of blood
• What happens to blood in arteries with each heartbeat?

  It surges through the arteries
• What can be felt in the wrist as blood surges through arteries?

  Your pulse
• What do elastic fibers in arteries do?

  Stretch and recoil with blood surges
• What is the function of capillaries?

  Facilitate diffusion of substances
• What substances diffuse from blood to cells in capillaries?

  Glucose and oxygen
• What is the structure of capillary walls?

  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 returns to the heart via veins
• What is a problem with blood in veins?

  It travels slowly under low pressure
• What is the structure of veins?

  Thin walls
• Why do veins have thin walls?

  Because blood pressure is low
• What do many veins contain to assist blood flow?

  Valves
• What is the function of valves in veins?

  To prevent backflow of blood
• 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 shut to prevent backflow
• What are the key features of arteries, veins, and capillaries?

  • Arteries: Thick muscular walls, elastic fibers, carry high-pressure blood
  • Veins: Thin walls, valves, carry low-pressure blood
  • Capillaries: Very thin walls, facilitate diffusion of substances