the heart and blood vessels

• heart


  an organ that pumps blood around the body
• circulatory system


  carries oxygen and other substances to bodily tissues to remove waste substances
• double circulatory system


  -one pathway carries blood from the heart to the lungs; where diffusion of oxygen and carbon dioxide takes place

  -the other pathway carries blood from the heart to the tissues
• blood pumped by the right ventricle ->

  the lungs
• blood pumped by the left ventricle ->

  body tissues
• importance of the double circulatory system


  makes the circulatory system more efficient

  e.g. oxygenated blood can be pumped around the body at a higher pressure by the left ventricle
• heart chambers


  4- right atrium, right ventricle, left atrium, left ventricle
• why is the wall of the left ventricle thicker

  the left ventricle has to pump blood at a higher pressure around the whole body
• four main blood vessels

  1. aorta (left) - carries oxygenated blood from the heart to the body
  2. pulmonary vein (left) - carries oxygenated blood from the lungs to the heart
  3. vena cava (right) - carries deoxygenated blood from the body to the heart
  4. pulmonary artery (right) - carries deoxygenated blood from the heart to the lungs
• valves


  prevent backflow of blood
• coronary arteries 


  supply the heart muscle with oxygenated blood
• describe the process of blood through the heart

  1. blood enters the right atrium via the vena cava, and the left atrium through the pulmonary vein
  2. the atria contract, forcing blood into the ventricles and causing valves to shut
  3. after the ventricles contract, blood in the right ventricle enter the pulmonary artery to the lungs, and blood enters the left ventricle through the aorta

  
• how is heart rate controlled


  by a group of cells in the right atrium which act as a pacemaker; they release waves of electrical activity which cause the heart muscle to contract
• abnormal heart rhythm 


  artificial pacemakers which send out electrical signals to correct the rhythm
• artery adaptations


  function: carry blood away from the heart

  -thick muscle layer adds strength to resist high pressure

  -thick elastic layer allows arteries to stretch and recoil in order to withstand high pressure
• veins adaptations


  function: carry blood towards the heart

  -wide lumen enables low pressure

  -valves prevent the backflow of blood
• capillaries adaptations


  function: enable transfer of substances between the blood and tissues

  -walls are one cell thick for a short diffusion path

  -narrow lumen so blood moves slowly which allows for more diffusion time