Chapter 11 — Chapter 11 — Human Circulatory System

Cone-shaped muscular organ in mediastinum, size of fist, in pericardium (fibrous + serous with pericardial fluid). Wall: epicardium (outer, visceral pericardium), myocardium (cardiac muscle — thickness varies), endocardium (endothelium lining, covers valves). Four chambers: two thin-walled atria (receive blood, pump only to ventricles), right ventricle (pumps to lungs — moderately thick), left ventricle (thickest, ~3× right, pumps to whole body against high resistance). Valves: tricuspid (right atrium–right ventricle), bicuspid/mitral (left atrium–left ventricle), pulmonary semilunar (right ventricle–pulmonary trunk), aortic semilunar (left ventricle–aorta); chordae tendineae and papillary muscles prevent eversion of AV valves. Flow: venae cavae → RA → tricuspid → RV → pulmonary semilunar → pulmonary arteries → lungs → pulmonary veins → LA → bicuspid → LV → aortic valve → aorta → body.