Transcript Document
Chapter 12 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 Outer layer = parietal pericardium Pericardial cavity is filled with pericardial fluid Approximately 15-30 ml pericardial fluid present 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 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 4 valves The heart is where pulmonary circulation starts and ends. The valves support 1-way movement through the heart. The heart acts as two pumps Right atrium and ventricle pump deoxygenated blood to the lungs Left atrium and ventricle pump oxygenated blood to the body Sequence of Blood Flow 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 Heart Actions Contraction is called systole Relaxation is called diastole These actions create Blood Pressure Practical Application Supposed an individual was injured by falling off a roof and he severely damaged his right arm with copious blood loss. His blood pressure steadily dropped to dangerous levels. How would you explain the drop in his blood pressure? Continued In response to the drop in blood pressure, the heart begins beating more rapidly. The increase in HR increases overall blood flow and thus causes even more rapid blood loss from a wound. The more blood lost, the faster the heart beats and the faster blood volume is lost. How can you explain this? What type of feedback is this? 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 Benefit of exercise! Conduction System of the Heart SA (sinoatrial) node The pacemaker In wall of right atrium near superior vena cava AV (atrioventricular) node AV bundle (bundle of His) In the floor of right atrium near septum 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 Issues with the heart’s conduction system Bradycardia—slow heart rate (under 60 beats/min) Tachycardia—rapid heart rate (over 100 beats/min) Sinus dysrhythmia—variation in heart rate during breathing cycle Premature contraction (extrasystole)—contraction that occurs sooner than expected in a normal rhythm Fibrillation—condition in which cardiac muscle fibers are “out of step,” producing no effective pumping action Chronic diseases of the heart Coronary Circulation and Coronary Heart Disease Blood, which supplies oxygen and nutrients to 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 CHD Atherosclerosis (type of “hardening of arteries” in which lipids build up on the inside wall of blood vessels) can partially or totally block coronary blood flow Angina pectoris—chest pain caused by inadequate oxygen to the heart Heart Failure Heart failure—inability to pump enough returned blood to sustain life; it can be caused by many different heart diseases Right-sided heart failure—failure of the right side of the heart to pump blood, usually because the left side of the heart is not pumping effectively Heart Failure Left-sided heart failure (congestive heart failure)— inability of the left ventricle to pump effectively, resulting in congestion of the systemic and pulmonary circulations Diseased hearts can be replaced by donated living hearts (transplants) or by artificial hearts (implants), although both procedures have yet to be perfected