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Transcript
The Heart General Information The heart is situated between the lungs and behind the sternum. About 2/3 of it lies to the left of the body’s midline. The heart is the size of a clenched fist. Structure of the Heart Pericardium = Outer double layered membrane of the heart – it reduces friction to maintain the hearts shape. Myocardium = Specialised cardiac muscle tissue. Cardiac muscles are involuntary. It is responsible for the contraction of the heart. Endocardium = Smooth inner membrane which lines the cavities of the heart- it prevents friction between the heart and the blood. The left hand side is bigger than the right – it has further to pump the blood. Cardiac Cycle 1. The Pulmonary Vein carries oxygenated blood from the lungs to the heart. 2. The Aorta carries oxygenated blood from the Heart to the body. 3. The Inferior and Superior Vena Cava carry deoxygenated blood from the body to the heart. 4. The Pulmonary Artery carries deoxygenated blood from the heart to the lungs. PV LA Aortic Valve Inferior Vena Cava Bicuspid Valve Aorta LV Body Semilunar Superior & RA Tricuspid Valve Semilunar Pulmonary Valve Pulmonary Artery RV Lungs 1. Pulmonary Circulation Lungs Pulmonary Vein Heart blood) Pulmonary Artery Heart (oxygenated blood) Lungs (deoxygenated 2. Systematic Circulation Heart Body Aorta Vena Cava Body (oxygenated blood) Heart (deoxygenated blood) Circulatory Systems There are 2 circulatory systems. 1 molecule of blood travels through the heart 2 times in a full cycle. Both parts of the heart work simultaneously (double pump) 1 beat takes approximately 0.8 seconds Lub noise = closing of the Bicuspid and Tricuspid valves. Dub noise = closing of the Semilunar valves Heart Diagram – Complete Labelling 1. Aorta 2. Superior Vena Cava 3. Pulmonary Artery 4. Right Atrium 5. Pulmonary Semilunar Valve 6. Tricuspid Valve 7. Inferior Vena Cava 8. Right Ventricle 9. Pulmonary Vein 10. Bicuspid Valve 11. Aortic Semilunar Valve 12. Left Ventricle Cardiac Cycle At rest, one complete cycle lasts 0.8 seconds and is repeated approximately 72 times a minute. The cardiac Cycle consists of two phases that represent the contraction and relaxation of the heart muscle. 1. Diastole – Relaxation phase (0.5 seconds) 2. Systole – Contraction phase (0.3 seconds) DIASTOLE *Both Atria fill with blood. Atrioventricular(AV) valves (bicuspid and tricuspid) are closed. *Atrial blood pressure rises above ventricular pressure. *Rising blood pressure forces the AV valves to open and blood passively passes into both ventricles. * Back-flow of blood into the ventricles from major blood vessels is prevented by the closed semilunar valves in the aorta and pulmonary artery. SYSTOLE After diastole the systole begins There are two phases of systole: – Atrial systole – Ventricular systole ATRIAL SYSTOLE *Muscle of both atria contract forcing the remaining atrial blood to move through the open AV valves into the ventricles. *The semi-lunar valves remain closed during this period VENTRICULAR SYSTOLE *Muscle tissue of both ventricles contract. *Aortic and pulmonary semilunar valves are forces open and the AV valves are shut to prevent back-flow of blood into atria. *Ventricle contraction forces open the SL valves *Blood is forced into: 1. Aorta to the body tissues/muscles. 2. Pulmonary Artery to the lungs. The heart then enters a period of diastole and the cycle is repeated. Conduction System The electrical impulse responsible for stimulating the heart to contract is called the cardiac impulse. Heart is myogenic – it generates its own electrical impulse. 1. The cardiac impulse is initiated from the sino-atrial (SA) node (often known as the pacemaker). 2. The impulse travels through the atria walls causing both atria to contract. The ventricles are insulated from the atria and cannot be stimulated at this point. 3. The cardiac impulse reaches and activates the Atrioventricular (AV) Node in the right atrium which passes the impulse down into the bundle of His located within the septum of heart. The AV node helps delay the impulse allowing the contraction of the atria to finish before the ventricles begin to contract. 4. The bundle of His splits into left and right branches and spreads the impulse down to the bottom of the heart and around the walls of the ventricles via a network of Purkinje fibres, causing both ventricles to contract. The ventricles then relax and the cycle is repeated with the next cardiac impulse. SA Node – Atria – AV Node – Bundles of His – Purkinje Fibres. Process can be known as “a wave of excitation”