7.THE CIRCULATORY SYSTEM: HEART

• The circulatory system includes the heart, which has a specific size, shape, and position, and is enclosed in the pericardium.
• The heart wall consists of the right and left ventricles, the right and left atria, and the septum.
• Some MIs are painless, “silent” heart attacks, especially in elderly or diabetic individuals.
• 17 isch = holding back; em = blood; ia = condition
• 15 infarct = to stuff
• Infarctions weaken the heart wall and disrupt electrical conduction pathways, potentially leading to fibrillation and cardiac arrest.
• 16 angina = to choke, strangle; pectoris = of the chest
• MI causes about 27% of deaths in the United States.
• The chambers of the heart include the right and left atria, the right and left ventricles, and the septum.
• The valves of the heart are the tricupid, mitral, and aortic valves.
• Blood flows through the chambers of the heart in a specific pattern.
• The coronary circulation is a part of the circulatory system that includes the heart and its surrounding vessels.
• Venous drainage is a part of the circulatory system that includes the heart and its surrounding vessels.
• Cardiac muscle and the cardiac conduction system are parts of the heart.
• The electrical and contractile activity of the heart is regulated by the cardiac rhythm, pacemaker physiology, impulse conduction to the myocardium, and the electrocardiogram.
• The cardiac cycle includes phases of the pressure and flow, heart sounds, and volume changes.
• Stress and hypertrophy of a ventricle can even- tually cause it to weaken and fail.
• Right ventricular failure due to obstructed pulmonary circulation is called cor pulmonale.
• A sustained program of exercise causes hypertrophy of the ventricles, which increases their stroke volume, allowing the heart to beat more slowly and still maintain a normal resting cardiac output.
• The effects of aging on the heart are discussed in section 29.4a, and some common heart diseases are listed in table 19.2.
• Cor pulmonale is a common complication of emphysema, chronic bronchitis, and black lung disease.
• Sympathetic output from the cardiac centers then increases cardiac output to meet the expected demand.
• The main reason the heart rate increases at the beginning of exercise is that proprioceptors in the muscles and joints transmit signals to the cardiac centers, signifying that the muscles are active and will quickly need an increased blood flow.
• Disorders of the blood and blood vessels are described in chap- ters 18 and 20.
• Exercise increases cardiac output by increasing the heart rate and stroke volume.
• As the right ventricle works harder to overcome this resistance, it gets larger like any other muscle.
• Some world-class, endurance- trained athletes have resting heart rates as low as 30 to 40 bpm, but because of the higher stroke volume, their resting cardiac output is about the same as that of an untrained person.
• Such athletes have greater cardiac reserve, so they can tolerate more exertion than a sedentary person can.
• As the exercise progresses, muscular activity increases venous return, which increases the preload on the right ventricle and is soon reflected in the left ventricle as more blood flows through the pulmonary circuit and reaches the left heart.
• The regulation of cardiac output hinges on the autonomic innervation of the heart, cardiac output, heart rate and chronotropic agents, stroke volume and inotropic agents, and exercise and cardiac output.
• The pericardium allows the heart room to expand, yet resists excessive expansion.
• The heart wall consists of three layers: epicardium, myocardium, and endocardium.
• In pericarditis —inflammation of the pericardium—the membranes may become roughened and produce a painful friction rub with each heartbeat.
• The fibrous pericardium is anchored by ligaments to the diaphragm below and the sternum anterior to it, and more loosely anchored by fibrous connective tissue to mediastinal tissue posterior to the heart.
• The heart isn’t inside the pericardial cavity but enfolded by it.
• The relationship of the heart to the pericardium is often described by comparison to a fist pushed into an underinflated balloon.
• The space between the parietal and visceral layers of the serous pericardium is called the pericardial cavity.
• The balloon surface in contact with the fist is like the epicardium; the outer balloon surface is like the parietal layer, and the air space between them is like the pericardial cavity.
• The pericardial cavity contains 5 to 30 mL of pericardial fluid, exuded by the serous pericardium.
• The fluid lubricates the membranes and allows the heart to beat with minimal friction.