뒤로Anatomy & Physiology: The Cardiovascular System - The Heart
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The heart has two side-by-side pumps: the right side pumps oxygen-poor blood to the lungs via the pulmonary circuit, and the left side pumps oxygenated blood to body tissues via the systemic circuit.
The heart is roughly fist-sized, located in the mediastinum between the second rib and fifth intercostal space, with about two-thirds left of the midsternal line.
The pericardium is a double-walled sac with a superficial fibrous layer and a deep serous layer (parietal and visceral layers) separated by a fluid-filled cavity to reduce friction.
Three layers: epicardium (visceral serous pericardium), myocardium (cardiac muscle with fibrous skeleton), and endocardium (endothelial lining of chambers and valves).
Four chambers: two atria (receiving chambers) and two ventricles (pumping chambers). Great vessels include the aorta, pulmonary trunk, venae cavae, and pulmonary veins.
Prevent backflow into atria during ventricular contraction. Right AV valve is tricuspid (3 cusps), left AV valve is mitral/bicuspid (2 cusps). Chordae tendineae anchor valve cusps to papillary muscles.
Prevent backflow from arteries into ventricles during relaxation. Pulmonary valve between right ventricle and pulmonary trunk; aortic valve between left ventricle and aorta. Each has three crescent-shaped cusps.
Right ventricle pumps to low-pressure pulmonary circuit; left ventricle pumps to high-pressure systemic circuit and has walls 3 times thicker.
Supplies blood to heart muscle itself via coronary arteries from the aorta; cardiac veins drain into coronary sinus and then right atrium.
Cardiac myocytes are short, branched, interconnected by intercalated discs containing desmosomes and gap junctions, allowing the heart to function as a syncytium.
Cardiac muscle has autorhythmic pacemaker cells, contracts as a unit, has longer refractory periods preventing tetanus, and relies mainly on aerobic respiration.
Network of autorhythmic cells including SA node, AV node, AV bundle, bundle branches, and Purkinje fibers that coordinate heartbeat.
Impulse starts at SA node → AV node → AV bundle → bundle branches → Purkinje fibers, completing ventricular depolarization in ~0.22 seconds.
Sympathetic stimulation increases heart rate and contractility; parasympathetic stimulation decreases heart rate via vagus nerve.
Rapid depolarization by Na+ influx, plateau phase due to Ca2+ influx, and repolarization by K+ efflux; long action potential prevents tetanus.
P wave: atrial depolarization; QRS complex: ventricular depolarization; T wave: ventricular repolarization.
Includes ventricular filling, isovolumic contraction, ventricular ejection, and isovolumic relaxation, coordinated with valve opening and closing.
First sound (lub) is AV valves closing at ventricular systole start; second sound (dup) is SL valves closing at ventricular diastole start.
CO = Heart Rate (HR) × Stroke Volume (SV); average adult CO is about 5.25 L/min at rest.
Preload (degree of muscle stretch), contractility (strength of contraction), and afterload (arterial pressure opposing ejection).
Influenced by autonomic nervous system, hormones (epinephrine, thyroxine), ions, age, sex, exercise, and body temperature.
Includes arrhythmias, fibrillation, heart block, congestive heart failure, and congenital defects like patent foramen ovale and tetralogy of Fallot.