6.2  The Blood System

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Essential Idea:

The blood system continuously transports substances

to cells and simultaneously collects waste products


  • Arteries convey blood at high pressure from the ventricles to the tissues of the body
  • Arteries have muscle cells and elastic fibres in their walls
  • The muscle and elastic fibres assist in maintaining blood pressure between pump cycles
  • Blood flows through tissues in capillaries
  • Capillaries have permeable walls that allow exchange of material between cells in the tissue and the blood in the capillary
  • Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart
  • Valves in veins and the heart ensure circulation of blood by preventing backflow
  • There is a separate circulation for the lungs
  • The heart beat is initiated by a group of specialised muscle cells in the right atrium called the sinoatrial node
  • The sinoatrial node acts as a pacemaker
  • The sinoatrial node sends out an electrical signal that stimulates contraction as it is propagated through the walls of the atria and then the walls of the ventricles
  • The heart rate can be increased or decreased by impulses brought to the heart through two nerves from the medulla of the brain
  • Epinephrine increases the heart rate to prepare for vigorous physical activity


  • William Harvey’s discovery of the circulation of blood with the heart acting as a pump
  • Pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle
  • Causes and consequences of occlusion of the coronary arteries


  • Identification of blood vessels as arteries, capillaries or veins from the structure of their walls
  • Recognition of the chambers and valves of the heart and the blood vessels connected to it in dissected hearts or in diagrams of heart structure