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The Cardiovascular System The Cardiovascular System • major function - transportation. • Uses blood as the vehicle • the system carries: –Oxygen – nutrients – cell wastes – hormones – and other substances vital for body homeostasis The Heart • The heart is located in the bony thorax – its apex is pointed towards the left hip and rests on the diaphragm. • Your heart is roughly the size of your fist. • Divided into four chambers Heart – Coverings • The heart is enclosed by a double sac called the pericardium. • Parietal Pericardium- loose outer layer, reinforced with fibrous tissue that helps protect the heart and anchor it to surrounding structures. • Visceral Pericardium – tightly hugs the external surface of the heart and is continuous with the heart wall. Heart - Walls • The heart walls are composed of three layers: 1. Visceral Pericardium (epicardium) 2. Myocardium – thick bundles of cardiac muscle twisted into ring-like arrangements (the contracting part) 3. Endocardium- thin sheet of epithelium that lines the chambers and is continuous with the blood vessels entering and leaving the heart. Heart - Chambers • The heart has 4 hollow chambers. • The superior two “receiving” chambers are called atria. • The inferior two “discharging” chambers are called ventricles. Heart – Great Vessels • Blood coming and going to and from the heart travels in blood vessels. • Veins carry blood away from the tissues towards the heart. • Arteries carry blood away from the heart. Key Great Vessels • Superior and Inferior Vena Cava – supply the right atrium. • Pulmonary Trunk (with R and L pulmonary arteries)– drain the right ventricle. • R and L Pulmonary Veins – supply the left atrium. • Aorta – drains the left ventricle. Blood Flow • The right side of the heart receives oxygen poor blood from the veins and pumps it through the pulmonary arteries to the lungs. • Now oxygen rich blood returns to the left side of the heart through the pulmonary veins. • This is Pulmonary Circulation Blood Flow • Oxygen rich blood in the left side of the heart is pumped into the aorta and travels to all the body’s tissues in systemic arteries. • It returns to the heart through systemic veins, and eventually the superior and inferior vena cava. • This is Systemic Circulation Valves • 4 valves which allow the blood to flow in only one direction through the chambers. Atrioventricular Valves • AV valves are between the atria and ventricles chambers on either side. • They prevent backflow into the atria when the ventricles contract. • Left AV valve – bicuspid valve • Right AV valve – tricuspid valve Semilunar Valves • The semilunar valves guard the bases of the two large arteries leaving the ventricular chambers. • Pulmonary Semilunar Valve – R ventricle to pulmonary trunk • Aortic Semilunar Valve – L ventricle to aorta Coronary Arteries • The blood supply that nourishes and oxygenates the heart is provided by the coronary arteries which stem from base of the aorta and encircle the heart. • These arteries fill when the heart is relaxed, and are compressed when the heart is contracting. Angina and Heart Attacks • If the heart beats at a very rapid pace it may receive inadequate blood supply • deprives the heart of oxygen and causing chest pain called angina. • If angina persists heart cells may die causing a myocardial infarction or “coronary”, otherwise known as a heart attack. Heartbeat • Unlike skeletal muscle cells, cardiac muscle cells contract independent of nerve stimulation in a regular and continuous way. • However, different areas of the heart beat in different rhythms. (Atria 60 bpm, Ventricles20-40 bpm) Controlling the Heartbeat • Autonomic nervous system - can increase or decrease heart rate. • Intrinsic Conduction System or Nodal System– causes heart depolarization in one direction (atria ventricle) and enforces the heart to beat at a unified contraction rate of approximately 75 beats per min. Intrinsic Conduction System • This nodal system is composed of special tissue found nowhere else in the body. It is like a cross between muscle and nervous tissue. • One of the most important parts is the sinoatrial node, located in the right atrium whose job it is to start each beat and set the pace for the whole heart. (the pacemaker) Intrinsic Conduction System • Form the SA node, the impulse spreads through the atria to the… • Atrioventricular (AV) Node where the impulse is delayed briefly to allow the atria to finish contracting. • It then passes rapidly through the AV bundle, the bundle branches, and the Purkinje fibers resulting in a contraction of the ventricles starting from the apex and moving toward the atria. The Cardiac Cycle • In a healthy heart the Atria contract together, then as they start they start to relax, the ventricles contract. • Systole- means contraction • Diastole – means relaxation • Because the ventricles do the pumping, these terms refer to the condition of the ventricle. The Cardiac Cycle Cardiac Cycle • Mid to Late Diastole – the heart is completely relaxed. The AV valves are open and the ventricles are filling. Then the atria contract. Cardiac Cycle • Ventricular Systole – Ventricle contraction begins and the AV valves close. Pressure builds in the ventricles, forcing open the semilunar valves, and blood is pumped out of the ventricles. • During this time the atria are relaxed and filling with blood. Cardiac Cycle • Early Diastole- The ventricles relax and the semilunar valves snap shut. When ventricular pressure drops below atrium pressure the AV valves open and blood again begins to fill the ventricles. Listening to your heart… • When you listen to your heart through a stethoscope you should be able to hear 2 distinct sounds: • Lub – the first is the longer and louder closing of the AV valves. • Dup- the second is the short and sharp closing of the semilunar valves. lub dup lub dup lub dup lub dup Blood Vessels • From the heart arteries smaller and smaller arteries arterioles capillary beds which feed the tissues and are drained by venules which empty into veins which empty into the great veins serving the heart. Blood Vessels • Blood is moved through the circulatory system by the elastic expansion and constriction of the blood vessels. • Vasoconstriction – reduction in the diameter of a blood vessel. • Vasodilation – enlargement of blood vessel diameter. Structure of Blood Vessels Arteries vs. Veins vs. Capillaries • Artery walls are much thicker than vein walls because arteries are closer to the pumping action of the heart and must be able to expand and recoil with that pumping action. Arteries vs. Veins vs. Capillaries • The pressure in veins tends to be low at all times, so they have thinner walls. Veins have larger lumen and some have valves to prevent back flow. Arteries vs. Veins vs. Capillaries • Capillary walls are only one cell layer thick and therefore allow for easy exchanges between blood and tissues. Circulation • The alternating expansion and recoil of an artery that occurs with each beat of the left ventricle creates a wave of pressure called a pulse. Blood Pressure • Blood pressure is the pressure the blood exerts against the inner walls of the blood vessels. • Continual blood flow depends on the stretchiness of the arteries and their ability to recoil and keep pressure on the blood. Measuring Blood Pressure • Two arterial blood pressure measurements are made. Systolic Pressure – the pressure in the arteries at the peak of ventricular contraction Diastolic Pressure – the pressure when the ventricles are relaxing Blood Pressure • Blood pressure depends on two main factors, - Cardiac output - Peripheral resistance • Anything that increases either of these factors, raises blood pressure. • • • • • Automatic nervous system Renal factors Temperature Chemicals Diet Measuring Blood Pressure