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The Circulatory System Section 33.1 Functions of the Circulatory System • Needed because the body has millions of cells. • Transports nutrients, oxygen, wastes, other substances. The Heart: Structure • The heart consists of – – – – – 4 chambers Numerous valves A muscle (cardiac) Hollow Septum separates right from left. • In the walls of the heart, 2 thin layers of connective and epithelial tissue sandwich a muscle called the myocardium. • Myocardium contracts and pumps blood through circulatory system. The Heart: Structure • Diagram The Heart: Blood Flow Right Atrium Superior/Inferior Vena Cava Pulmonary Veins Left Atrium Lungs Pulmonary Artery Mitral Valve Tricuspid Valve Right Ventricle Pulmonary Valve Left Ventricle Aorta Aortic Valve The Heart: Blood Supply • Coronary Arteries give blood to heart’s tissue. – Branch from aorta – Run through heart tissue – Narrow – If blocked, tissue may die=heart attack. The Heart: Circulation • Pulmonary – Right side of heart pumps to lungs. – Gas exchange occurs – Oxygen rich blood returns to left side of heart. • Systemic – Blood pumped from left side of heart to body. – Cells use oxygen – Oxygen poor blood comes back to right side of heart. The Heart: Heartbeat • 1. Atria Contract – Starts in right atrium – In a small muscle group, sinoatrial node (SA). • AKA pacemaker. – When SA node fires, electrical impulse spreads and muscle contracts. • 2. Ventricles Contract – Impulse from SA picked up by atrioventricular (AV) node. – Impulse delayed. – AV node produces impulses that spread through ventricles. – They contract. The Heart: Heart Rate • Varies depending on.. – Activity level – Oxygen need • Not directly controlled by nervous system. – Is influenced though Blood Vessels: Arteries • Oxygen rich blood to the tissues of the body and usually flow with gravity • Large (superhighways) • Thick walled…highly pressurized • Consist of connective tissue, smooth muscle, endothelium. Blood Vessels: Capillaries • Smallest vessels • Narrow, blood cells move single file • Thin walls Blood Vessels: Veins • Blood flows against gravity • Large veins near skeletal muscles, push blood towards heart. • Veins contain valves • Consist of connective tissue, smooth muscle, endothelium. Blood Pressure • System always under pressure due to arterial walls. • Pressure needed to make blood flow. • Blood pressure regulated by the nervous system, also kidneys.