The circulatory system and blood vessels

• The circulatory system is made up of the heart, blood, and blood vessels (arteries, veins, and capillaries)
• Arteries carry blood away from your heart to the organs of the body
• Veins carry blood back towards the heart
• The veins and arteries are inked by capillaries which form a huge network of tiny vessels
• In humans and other mammals, the blood vessels are arranged in a double circulatory system.

  • One transport system (pulmonary) carries blood from your heart to the lungs and back again. This allows oxygen and carbon dioxide to be exchanged
  • The other transport system (systemic) carries blood from your heart to all other organs of your body and back again
• Arteries structure:

  • Thick wall made of muscle and elastic tissue - stretches and recoils to maintain high blood pressure and help force the blood along, smoothing blood flow
  • Narrow (small) lumen
  • No valves
• Vein structure:

  • Relatively thin wall - no need of control of blood flow
  • Valves - prevent backflow because of low pressure
  • Large lumen
• Capillaries structure:

  • Extremely thin, one cell thick - short diffusion distance
  • Lumen is narrow - slows blood down and short diffusion distance