The Structure of Blood Vessels

• Blood flows within three main types of blood vessel:

  • Arteries
  • Veins
  • Capillaries
• Arteries

  • Arteries carry blood away from the heart at high pressure
  • The blood within arteries is oxygenated
  • —> With the exception of the pulmonary artery
• Structure of the Arteries

  • Thick muscular walls —> withstand the high pressure of blood
  • Elastic tissue —> within the walls allows arteries to stretch and recoil to their original shape; this maintains high blood pressure
  • A narrow lumen —> helps to maintain high pressure
• Vasoconstriction

  Arterioles supplying the digestive system constrictduring exercise, resulting in a reduced diameter that restricts blood flow
• Vasodilation

  Arterioles supplying the muscles dilate during exercise, resulting in an increased diameter and increased blood flow
• • Vasodilation increases the quantity of oxygen and glucose being delivered to the respiring cells
• The muscle in the walls of small arteries (arterioles), can contract or relax to alter the diameter of the blood vessel lumen; this allows blood to be redistributed to different organs
• Veins

  • Veins carry blood towards the heart at low pressure
  • The blood within veins is deoxygenated
  • —> With the exception of the pulmonary vein
• • The walls of veins are thinner than the walls of arteries as they do not need to withstand high blood pressure
• Structure of the Veins

  • wide lumen —> to allow large volumes of blood to flow
  • The presence of valves prevents blood from flowing backwards
• Capillaries

  • These are very small blood vessels that carry blood to the cells of the body at low pressure
  • Oxygen and nutrients diffuse out of capillaries to the cells
  • Carbon dioxide diffuses from the cells into capillaries
• • The blood in capillaries may be either oxygenated or deoxygenated
• Structure of the Capillaries

  • Walls that are one cell thick,—> reducing the diffusion distance for gas exchange 
  • Capillaries have a very narrow lumen; this forces red blood cells to flow one at a time and allows diffusion to occur
  • There are many capillaries, providing a very large surface area
• Blood vessels of the heart

  • Vena Cava
  • Pulmonary Artery
  • Pulmonary Vein
  • Aorta
• The Vena Cava

  The main vein that carries deoxygenated blood from the body to the heart
• The Pulmonary Artery

  Carries deoxygenated blood from the heart to the lungs
• The Pulmonary Vein

  Carries oxygenated blood from the lung to the heart
• The Aorta

  The main artery that carries oxygenated blood from the heart to the body