Blood vessels

• Arteries


  Carry high pressure blood away from the heart to the organs and tissues, have thick muscular walls and a relatively narrow Lumen
• Blood flow in arteries


  1. Arteries lead to smaller vessels called arterioles

  2. Arterioles split off into capillaries which form a network throughout the organs and tissues
• Capillaries


  Facilitate the exchange of oxygen, carbon dioxide, food molecules and other substances between the blood and surrounding cells, have an extremely narrow Lumen and permeable walls only one cell thick
• Blood flow in capillaries


  1. Part of the blood plasma is forced through the walls of the capillaries and into the cells

  2. Tissue fluid containing dissolved substances moves in the other direction
• Veins


  Transport blood back to the heart, have thinner walls and a wide Lumen than arteries, contain pocket valves to prevent the backflow of low pressure blood
• Arteries


  • Thick muscular walls with elastic fibers and fibrous tissue to maintain the waves of pressure generated by the heart and prevent damage
  • Relatively narrow Lumen to maintain high pressures
  • No valves as they're close to the heart, pressure is sufficient to prevent backflow
• Veins


  • Much thinner walls with less muscle and fewer elastic fibers
  • Large Lumen which lowers resistance and allows the blood to flow more easily
  • Contain valves as blood pressure is insufficient to prevent backflow
• Capillaries


  • Extremely thin permeable walls made of a single layer of cells to reduce the diffusion distance
  • Very narrow Lumen which slows down blood cells to facilitate the diffusion of materials
  • No valves as pressure is still high enough to prevent backflow
• Main blood vessels of the heart and lungs

  • Vena cava
  • Pulmonary artery
  • Pulmonary vein
  • Aorta
• Blood flow through the heart and lungs

  1. Deoxygenated blood flows into the right atrium through the vena cava

  2. Blood moves down into the right ventricle, into the pulmonary artery and off to the lungs

  3. Oxygenated blood from the lungs flows through the pulmonary vein and into the left atrium

  4. It then moves down into the left ventricle which contracts forcing it into the aorta and around the body
• Main blood vessels of the kidneys


  • Renal artery
  • Renal vein
• Main blood vessels of the liver


  • Hepatic artery
  • Hepatic portal vein
  • Hepatic vein
• Blood flows into the liver through


  • Hepatic artery (carries oxygenated blood from the aorta)
  • Hepatic portal vein (delivers blood rich in nutrient molecules from the stomach and small intestines)
• Blood flows out of the liver through

  Hepatic vein (returns deoxygenated blood to the vena cava)