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Transcript
Chapter 13 The Heart Location, Size, and Position of the Heart • In mediastinum • 2/3 to the left of the body midline • Apex = point – Most inferior portion • Shape and size of a closed fist • Septum divides right and left sides (internally) Pericardium • Two-layered fibrous sac – Inner layer = visceral pericardium or epicardium – Pericardial Cavity filled with pericardial fluid – Outer layer = parietal pericardium Three layers of the Heart Wall – Epicardium • Outer layer • Connective tissue – Myocardium • Middle layer • Thick • Muscle – Endocardium • Inner layer (lining) • Very thin, smooth Summary of layers • Outside (external) to Inside (internal) • • • • • Parietal Pericardium Pericardial cavity (filled with fluid) Visceral Pericardium/Epicardium Myocardium Endocardium Coronary Circulation • Blood for the myocardium of the heart, flows through the right and left coronary arteries • Blockage of blood flow through the coronary arteries can cause myocardial infarction (heart attack) Anatomy of the Heart • Heart chambers – Two upper chambers are • Right and left atria (atrium) • Small chambers • Receive blood – Two lower chambers called ventricles • Right and left ventricles • Larger chambers • Pump blood out of heart Vessels • Pulmonary Arteries – Carry blood from R ventricle to lungs – R pulmonary artery to R lung – L pulmonary artery to L lung • Pulmonary Veins – Carry blood from lungs to L atria – R pulmonary veins from R lung – L pulmonary veins from L lung Vessels cont. • Vena Cava – Inferior and superior – Empties blood into heart from body Valves – Cuspid valves • Tricuspid: between right atrium and ventricle • Bicuspid (mitral): between left atrium and ventricle • Open and close from chordae tendineae – Semilunar valves • Pulmonary Semilunar: base of pulmonary arteries • Aortic Semilunar: base of aorta • Open and close from pressure within heart The heart acts as two pumps Right atrium and ventricle pump deoxygenate blood to the lungs Left atrium and ventricle pump oxygenated blood to the body Blood Flow Pathway • Superior and Inferior Vena Cava • Right atrium • Tricuspid valve • Right ventricle • Pulmonary Semilunar Valve • Pulmonary Arteries • Lungs • • • • • Pulmonary Veins Left atrium Bicuspid valve Left Ventricle Aortic Semilunar Valve • Aorta • Body Conduction System of the Heart – SA (sinoatrial) node • The pacemaker • In wall of right atrium near superior vena cava – AV (atrioventricular) node • In the floor of right atrium near septum – AV bundle (bundle of His) • Located in the septum of the ventricle – Purkinje fibers— • Located in the walls of the ventricles • Cause contraction of myocardium Conduction System of the Heart • Electrocardiography – Measures the electrical impulses that result in contraction of the heart – Impulses transformed into visible tracings by a machine called an electrocardiograph – The visible tracing of these electrical signals is called an electrocardiogram or ECG Conduction System of the Heart – The normal ECG has three deflections or waves called the P wave, the QRS complex, and the T wave • P wave—associated with depolarization of the atria • QRS complex—associated with depolarization of the ventricles • T wave—associated with repolarization of the ventricles Some other odds and ends… Heart Actions • Contraction is called systole • Relaxation is called diastole Heart Sounds • Two distinct heart sounds in every heartbeat or cycle—“lubb-dupp” • First (lubb) sound is caused by the vibration and closure of AV valves during contraction of the ventricles • Second (dupp) sound is caused by the closure of the semilunar valves during relaxation of the ventricles Cardiac Cycle • Heart beat is regular and rhythmic—each complete beat called a cardiac cycle— average is about 72 beats per minute • Each cycle, about 0.8 seconds long, subdivided into systole (contraction phase) and diastole (relaxation phase) Cardiac Cycle • Stroke volume is the volume of blood ejected from one ventricle with each beat • Cardiac output is amount of blood that one ventricle can pump each minute—average is about 5 L per minute at rest