Transcript Slide 1
The Show 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 – 300g • Size – of Your fist • Beats – 70 times per minute • Cardiac muscle – contracts and relaxes naturally Cross section of the Heart Oxygenated blood leaves the left ventricle to circulate through the body Receives blood from the venae cavae Control the flow & backflow of blood Carries deoxygenated blood away from the heart vena cava from the head Upper left chamber Upper right chamber vena cava from lower body Deoxygenated blood flows into the pulmonary arteries Lower right chamber Lower left chamber Receives blood from the pulmonary veins Control the flow & backflow of blood Oxygenated blood flows into the aorta. 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 atrioventricular valves shut But how does it work? 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 > 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 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 Bibliography • Biology 1 – pgs 120-127 • http://www.patient.co.uk/showdoc/21692435/