The heart

The heart

1. Structure

   • Atrium
     • Thin-walled
       • Pumps short distance - ventricle
     • Elastic
     • Stretches as blood is collected
   • Ventricle
     • Thick-walled
     • Pumps to lungs/whole body
   • Aorta
     • Connected to LV
     • Carries oxygenated blood to body
   • Vena Cava
     • Connected to right atrium
     • Brings deoxy blood back from body
   • Pulmonary artery
     • Connected to right ventricle
     • Deoxy blood from lungs
       • Unusual for artery to carry deoxygenated
   • Pulmonary vein
     • Connected to left atrium
     • Brings oxygenated blood from lungs
       • Unusual for vein to carry oxygenated

2. Cardiac cycle

   • 1) Electrical activity SAN -> across both atria -> atria contract
   • 2) Collagen stops wave crossing to ventricles
   • 3) Wave passes to AVN
   • 4) Electrical impulse -> bundle of His
   • 5) Wave -> down septum to base of ventricles, bundle branches into smaller fibres
   • 6) wave released from fibres -> ventricles contract apex up.
   • Diastole
     • Blood returns to atria through pulmonary vein & vena cava
     • As atria fill, pressure ^ -> AV valves open
     • Walls of atria + Ventricles relaxed
       • Relaxation of ventricles reduces pressure - lower than aorta/pulmonary artery
         • SL valves close. "Dub"
   • Atrial systole
     • Atria contracts, forcing remaining blood into ventricles
     • thin walls as only to ventricles
     • Ventricles relaxed
   • Ventricular systole
     • Walls contract simultaneously once full
     • Increases pressure - shuts AV valves "lub"
       • SL open -> blood pushed into pulmonary artery & aorta
     • Thick walls as pump to lungs/body
   • Myogenic

3. Supplying heart with O2

   • Coronary arteries branch off aorta shortly after leaving heart
     • Blockage here leads to myocardial infarction

4. Valves

   • Atrioventricular
     • between atrium&ventricle
     • Prevent backflow when ventricles contract
   • Semi-lunar
     • In aorta&pulmonary artery
     • Prevent backflow when recoil in aorta/pulmonary artery causes pressure to exceed that in ventricles

5. Cardiac output

   • heart rate x stroke volume
   • Heart rate
     • Rate of heart beat
   • Stroke volume
     • Vol. blood pumped out at each beat