The Big Picture
  • Blood with oxygen comes from the lungs
    • into the left atrium (LA)
    • past the mitral valve
      • the mitral valve is held into place by strands of tissue called chordae tendinae
      • these attach to the muscle of the left ventricle (by papillary muscles)
    • into the left ventricle (LV)
      • the main pumping chamber of the heart
  • Blood with oxygen is delivered to the body
    • from the left ventricle (LV)
      • the main pumping chamber of the heart
    • past the aortic valve
    • into the aorta (Ao) and body blood vessels
  • Blood without oxygen comes from the body
    • into the right atrium (RA)
    • past the tricuspid valve
      • the tricuspid valve is also held into place by strands of tissue called chordae tendinae
      • these attach to the muscle of the right ventricle (by papillary muscles)
    • into the right ventricle (RV)
      • the pumping chamber for the lungs
  • Blood without oxygen is delivered to the lungs to get oxygen
    • from the right ventricle (RV)
      • the pumping chamber for the lungs
    • past the pulmonic valve
    • into the pulmonary artery (PA) and to the lungs

Mechanics
  • Blood with oxygen comes from the lungs
    • into the left atrium (LA)
      • the left atrium is a low pressure receiving chamber
      • it also actively contracts to force some of the blood (about 20%) into the left ventricle
    • past the mitral valve
      • the mitral valve is a passive, one-way valve, opening and closing by blood flow
    • into the left ventricle (LV)
      • the main pumping chamber of the heart
        • pressures within the left ventricle when it is contracting (systole) are about 120mm Hg
          • normal blood pressure for most mammals
        • pressures within the left ventricle when it is relaxed (diastole) are very low, nearly 0mm Hg
  • Blood with oxygen is delivered to the body
    • from the left ventricle (LV)
      • the main pumping chamber of the heart
    • past the aortic valve
      • the aortic valve is also a passive, one-way valve, opening and closing by blood flow
        • however, it has to keep blood pressure up within the body when the heart is relaxing (diastole) so that blood in the body always moves forward
    • into the aorta (Ao) and body blood vessels
      • so, pressures during systole (contraction) in the body are about 120mm Hg, and during diastole (relaxation) are about 80mm Hg
        • And… your classic 120/80 is about what all mammals maintain
  • Blood without oxygen comes from the body
    • into the right atrium (RA)
      • the right atrium is a low pressure receiving chamber
    • past the tricuspid valve
      • the tricuspid valve is a passive, one-way valve, opening and closing by blood flow
    • into the right ventricle (RV)
      • the pumping chamber for the lungs
  • Blood without oxygen is delivered to the lungs to get oxygen
    • from the right ventricle (RV)
      • the pumping chamber for the lungs
        • pressures within the right ventricle when it is contracting (systole) are much lower than in the left ventricle, only about 20mm Hg
          • the right ventricle is not designed to handle high blood pressures within the lungs
    • past the pulmonic valve
      • the pulmonic valve is also a passive, one-way valve, opening and closing by blood flow
        • it has to keep blood pressure up within the lungs when the heart is relaxing (diastole) so that blood in the lungs always moves forward
    • into the pulmonary artery (PA) and to the lungs
      • so, pressures during systole (contraction) in the lungs are about 20mm Hg, and during diastole (relaxation) are about 10mm Hg
        • And… normal lung blood pressures are about 20/10
        • If there is severe high blood pressure in the lungs, the pressure can go as high as that in the body (120/80), and the right side of the heart is not designed to handle this well

Electrical
  • In the right atrium
    • an electrical signal is generated from the SA (sinoatrial) node (red circle)
  • this spreads across both the right and left atria
    • and causes both atria to mechanically contract and force blood into the ventricles
  • this node controls overall heart rate
  • At the junction of the atria and ventricles
    • the electrical signal goes to the AV (atrioventricular) node (blue circle)

      • this node controls delay so that the atria and ventricles are contracting in controlled synchrony
  • In the ventricles
    • the electrical signal then spreads through the left and right ventricles by specialized tissue
      • and causes both ventricles to mechanically contract and force blood to the body and lungs
Electrical Problems
  • The SA node can fire too fast or too slow
    • this causes either too low or too fast of heart rates
      • the SA node is also controlled by other factors, and it may not be an SA node problem
  • The atria can start to generate, fast random electrical signals
    • this is called atrial fibrillation
      • not only is overall heart rate often too high and chaotic
      • there is loss of the mechanical contribution of the atria, causing about 20% loss of heart function
  • The AV node can become diseased and not transmit signals effectively
    • this is a “block” of the signals, then overall heart rate drops very significantly
    • with a complete block, the ventricles will generate a “fail-safe” signal so there are some contractions
      • this rate is very low, often in the 30’s
      • a pacemaker is usually required to correct this