Blood Circulation

• Double Circulation


  • Movement of blood in a double circulation from the heart to the lungs to the heart and from the heart to the rest of the body back to the heart
  • In a double circulation, the blood has to pass through the heart twice in one complete circuit.

  
• Main Blood Vessels


  • pulmonary vein
  • pulmonary artery
  • hepatic artery
  • hepatic portal vein
  • hepatic vein
  • renal artery
  • renal vein
• The Structure and Function of the Heart

  1. Four chambers

  • Two atria (right atrium, left atrium)

  • Two ventricles (right ventricle, left ventricle)

  2. Median septum

  3. Valves

  • tricuspid valves

  • bicuspid valves

  • aortic valves (semi-lunar valves in the aorta)

  • pulmonary valves (semi-lunar valves in the pulmonary artery)

  
• Valve


  • Blood should move from atrium to ventricle
  • Blood moves from area of high pressure to low pressure
  • Ventricular pressure exceeds the atrial pressure when the muscular walls of the ventricles are contracting to force blood out of the heart
  • Blood would move from the ventricle to the atrium, from area of higher pressure to lower pressure
  • The atrioventricular valves in the heart will be forced close when the pressure in the ventricles exceeds the pressure in the atria, preventing blood from backflowing from ventricles into atria.
• Hole in the Heart


  • The hole in the median septum will result in the mixing of oxygenated and deoxygenated blood, thereby reducing the concentration gradient for oxygen (and carbon dioxide) and reduces efficiency of gas exchange
  • This condition may cause problems such as shortness of breath, fatigue and heart failure.
• Systole and Diastole


  Systole = Contraction

  Diastole = Relaxation

  Atrial systole - Atrium contracts

  Atrial diastole - Atrium relaxes

  Ventricular systole - Ventricle contracts

  Ventricular diastole - Ventricle relaxes
• Cardiac Cycle


  • One cardiac cycle consists of one ventricular systole and one ventricular diastole

  
• Cardiac Cycle Graph (part 1)


  1. slight increase in ventricular pressure due to contraction of left atrial muscles, forcing blood into ventricle
  2. ventricular muscles begin to contract, bicuspid valve closes
  3. ventricular muscles continue to contract without change in volume of blood, pressure continues to rise
  4. pressure in ventricle becomes higher than in aorta. Semi-lunar valve in aorta opens. Blood is forced out into the aorta, volume of blood in ventricle decreases

  
• Cardiac cycle Graph (part 2)

  6. Ventricular muscles continue to relax without change in volume of blood

  7. Bicuspid valve opens when pressure in ventricle becomes lower than in atrium

  8. Pressure in ventricle rises as blood continues to enter ventricle from atrium