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Heart ACCESS H.E. HUMAN BIOLOGY. Clare Hargreaves-Norris Heart structure The heart is a hollow, cone shaped organ with cardiac muscle forming its walls. There are three layers which form the walls of the muscle: endocardium, myocardium and pericardium. The heart is approximately 10 cm long and is situated in the thoracic cavity, behind the sternum, lying to the left side. The heart is divided into a right and left side with the septum separating each side. The heart contains four chambers; two upper chambers called the right and left atriums and two lower chambers called the right and left ventricles. The valves separate the atrium and ventricle chambers and when they open and close they change the pressure within the chambers. Clare Hargreaves-Norris Contraction and relaxation of the heart When the cardiac muscle contracts (at systole) it forces the blood out of the heart and into the arteries which carry the blood around the body. When the cardiac muscle relaxes (at diastole) the heart fills with blood. This mechanism of contraction and relaxation is known as a heart beat. Clare Hargreaves-Norris The sequence the blood flows through the heart 1. 2. 3. 4. 5. 6. Deoxygenated blood returns from the body via the superior and inferior vena cava into the right atrium of the heart. The blood is squeezed through the tricuspid valve into the right ventricle. It is then forced out into the pulmonary artery which transports the deoxygenated blood to the lungs to become oxygenated. The oxygenated blood from the lungs enters into the left atrium of the heart via the pulmonary veins. The blood is squeezed through the bicuspid valve into the left ventricle. It is then forced into the body’s largest artery - the aorta, which transports the oxygenated blood to the rest of the body. 6 1 4 3 5 2 Clare Hargreaves-Norris The Heart The Heart Clare Hargreaves-Norris Pulmonary & Systemic Circulatory Systems Two distinct systems Clare Hargreaves-Norris Pulmonary circulation Pulmonary circulation transports blood from the lungs to the heart and back. Deoxygenated blood is taken via the pulmonary artery from the right ventricle of the heart to the lungs. The lungs enrich the blood with oxygen. Carbon dioxide is removed from the blood. Pulmonary veins carry the oxygenated blood back to the left atrium of the heart. Clare Hargreaves-Norris Systemic circulation Systemic circulation transports blood from the heart to the rest of the body and back. It carries oxygenated blood from the left ventricle via the aorta to the body organs and tissues. The aorta branches off to supply the various areas of the body. As the blood travels around the body, the oxygen is removed. Carbon dioxide is picked up by the blood. The superior and inferior vena cava returns the deoxygenated blood back to the heart. Clare Hargreaves-Norris