cardiac cycle

• list the pathway of blood through the heart

  vena carva

  right atrium

  AV valve

  right ventricle

  SL valve

  pulmonary artery

  lungs

  pulmonary veins

  left atrium

  AV valve

  left ventricle

  SL valve

  aorta
• what is the function of valves

  prevent backflow of blood
• what causes valves to open can close

  pressure changes
• what causes a valve to open

  when pressure is greater behind the valve
• what causes a valve to shut

  when the pressure is greater in front of the valve
• what is the cardiac cycle

  An ongoing sequence of contraction and relaxation of the atria and ventricles that keeps blood continuously circulating round the body
• stage 1 of the cardiac cycle

  atrial and ventricular diastole:

  atria and ventricles relax

  the higher pressure in the pulmonary artery and aorta causes the SL valves to close

  blood enters the atria, so its pressure increases causing the AV valves to open and blood flows passively into the ventricles
• stage 2 of the cardiac cycle

  atrial systole:

  atria contract, which decreases their volume and increases their pressure, this pushes blood into the ventricles through the AV valve so the volume increases and pressure increases.
• stage 3 of the cardiac cycle

  ventricle systole:

  atria relax

  ventricles contract, decreasing their volume and increasing their pressure so the AV valves close

  SL valves open so blood flows into the aorta and pulmonary artery
• formula for cardiac output

  cardiac output = heart rate x stroke volume
• what is cardiac output

  volume of blood pumped by the heart per minute
• what is heart rate

  number of beats per minute
• what is stroke volume

  volume of blood pumped during each heartbeat
• what is the lub caused by

  closing of AV valves
• what is the dub caused by

  closing of semilunar valves
• what is special about cardiac muscle

  its myogenic so it contracts and relaxes without receiving signals from nerves
• how is the heart rhythm coordinated

  SA node and AV node
• what is the SAN called

  pacemaker
• describe how the nodes control the heart

  1) the SAN sends a wave of depolarisation across the atrias, causing them to contract

  2) the non-conductive layer of tissue between the atria and ventricles prevents the wave travelling to the ventricles

  3) instead, the waves reach the AVN

  4) the AVN sends a wave down the bundle of His, but there's a slight delay before the AVN reacts to make sure the ventricles contract after the atria have emptied

  5) the wave travels along the bundle of His to the purkyne fibres in the walls of the ventricles causing them to contract

  6) the nodes repolarise
• where is the SAN

  wall of right atrium