The Heart <3

The Heart <3

1. Cardiac output- volume of blood pumped by the heart per minute

   • cardiac output = stroke volume x heart rate
     • Heart rate- number of heartbeats per minute. Can measure by feeling your pulse (surges of blood forced through arteries by heart contracting)
     • Stroke volume- volume of blood pumped during each heartbeat

2. Cardiac cycle- pumps blood round body

   • Ongoing sequence of contraction/relaxation of atria and ventricles. Keeps blood continuously circulating round body.
     • Volume of atria and ventricles change. Pressure changes also occur due to changes in chamber volume.
   • 3 stages
     • Ventricles relax, Atria contract. This decreases the volume of the chamber and increases pressure. Pushes blood into ventricles. Slight increase in ventricular pressure and chamber volume as they receive ejected blood.
       • Ventricles contract, Atria relax. Decreases volume and increases pressure. Pressure becomes higher in ventricles than atria- forces AV valves shut to prevent back-flow. Pressure in ventricles also higher in aorta and pulmonary artery so forces open SL valves & blook forced out into arteries.
         • Ventricles relax, Atria relax. Higher pressure in pulmonary artery and aorta closes SL valves to prevent back-flow into ventricles. Blood returns to heart and atria fill again due to higher pressure in vena cava and pulmonary vein. Starts to ^ pressure of atria. As ventricles relax pressure falls below that of atria so AV valves open. Allo w blood to flow passively into ventricles. Atria contract & process begins again...