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Introduction to Physiology Lecture 3: Functions of Circulatory System: • Transportation – O2, CO2, metabolic wastes, nutrients, hormones, medications and heat. • Regulation – pH within body through buffers, composition of intracellular fluid, body temperature (coolant properties of water – absorbs heat with little change to temp, carries heat to body surface for loosing excess). • Protection – from disease (immunity, inflammation) The heart: Base – Superior surface of the heart Apex – inferior pointed tip Layers of the heart wall: Myocardium – Middle, muscular layer (contains cardiac muscle tissue, blood vessels, and nerves) Endocardium – Lines the inner surfaces of the heart, including valves. Forms endothelium continuous with blood vessels endothelium. Epicardium • Visceral pericardium – Serous membrane covers surface of heart and attached myocardium • Parietal pericardium – not a heart wall layer but is continuous serous membrane with visceral pericardium. Pericardial cavity – between the Epicardium (visceral) and the parietal pericardium. Contains serous fluid. Cardiac muscle: Features • Only in heart • Cells are striated to organized myofibrils • Single, centrally located nucleus • Intercalated disks o Contain: § Desmosomes § Gap Junctions – Allow ions and molecules to move directly between cells; Create direct electrical connection so an action potential can pass directly between cells. o Stabilize relative positions of adjacent cells o Myofibrils allow to ‘pull together’ for maximum efficiency o Functional syncytium – Cells so connected that they all act as a single muscle cell. Energy Requirements • Aerobic metabolism for ATP o Large numbers of mitochondria to store O2 o Large numbers of capillaries to supply nutrients and O2 • Is adaptable, can switch from glucose to an alternative nutrient source (lactic acid, or fatty acid) • Fatigue resistant Blood supply to cardiac muscle – Coronary circulation Right coronary artery – Supplies the right atrium and portions of both ventricles. Left coronary artery – Supplies the left ventricle, left atrium and interventricular septum. Internal heart anatomy Right Atrium • Receives blood from the superior vena cava and inferior vena cava. Right Ventricle • Blood travels from the R.A to the R.V through an opening of the atrioventricular (AV) valve, a tricuspid valve. • The blood is then pushed through the pulmonary semilunar valve into the pulmonary trunk, where the blood is oxygenated in the lungs. Left Atrium: • The oxygenated blood returns to the L.A through the pulmonary veins. Left Ventricle • The blood is passed from the L.A through an AV valve, a bicuspid valve. • The L.V has thicker muscular walls to develop pressure sufficient enough to push blood throughout all the circulatory system. • Blood leaves the L.V through the aortic semilunar valve, into the ascending aorta. Interatrial septum – Separates the atria Interventricular septum – separates ventricles by thick muscular wall