1. The Show

2. The Heart The heart is a bag of cardiac muscle filled with blood Has 4 chambers: 2 atria & 2 ventricles Right side contains oxygenated blood Left side contains deoxygenated blood Mass – 300 g Size – of Your fist Beats – 70 times per minute Cardiac muscle – contracts and relaxes naturally

3. Cross section of the Heart Carries deoxygenated blood away from the heart Upper left chamber Oxygenated blood leaves the left ventricle to circulate through the body Receives blood from the venae cavae Deoxygenated blood flows into the pulmonary arteries Oxygenated blood flows into the aorta. Receives blood from the pulmonary veins Lower right chamber Upper right chamber Lower left chamber vena cava from lower body Control the flow & backflow of blood vena cava from the head Control the flow & backflow of blood

4. But how does it work? 1.Atrial systole stage: The heart fills with blood > the atrial wall muscle contracts 2.The pressure forces the blood in the atria down into the ventricles 3.Semilunar valves prevent blood backflow 4.Ventricular systole stage: the ventricle thick muscular wall squeezes inwards > increasing pressure pushes the blood out of the heart 5.Backflow is prevented by the pressure difference that pushes the atrio- ventricular valves shut

5. But how does it work? Blood moves downwards into ventricles through the atrio-ventricular valves > the atrial muscle contracts to push the blood forcefully down into the ventricles > 8.The cycle begins again 6.The blood rushes upwards into the aorta & the pulmonary artery pushing open the semilunar valves 7.Ventricular diastole stage: all the heart muscles relax > low pressure blood from the veins flows into the 2 atria >

6. How is it controlled? The cardiac cycle – sinoatrial node (SAN) or the pacemaker SAN contracts > a wave of electrical activity spreads out quickly over the atrial walls > the cardiac muscle in the atrial wall responds by contracting at the same rhythm as the SAN SAN can’t pass into the ventricle walls Atrio-ventricular node (AVN) fibres pick up the wave > pass it on to conducting fibres called Purkyne tissue > which then transmit the wave quickly through the ventricle walls

7. Bibliography Biology 1 – pgs 120-127 http://www.patient.co.uk/showdoc/21692435/