Cardiovascular System Anatomy

Structure of the Heart

• The heart lies within a fibroelastic sac called the pericardium
• The wall of the heart is composed of three layers: epicardium, myocardium, and endocardium
• The heart has four major blood vessels: vena cava, pulmonary artery, pulmonary vein, and aorta
• The heart has four chambers: right atrium/auricle, right ventricle, left atrium/auricle, and left ventricle
• The heart has four valves: tricuspid, pulmonic semilunar, mitral, and aortic semilunar

Cardiac Conduction System

• The cardiac conduction system consists of the Sinoatrial node (SAN), atrioventricular node (AVN), atrioventricular (AV) bundle, and Purkinje fiber network
• The myocardium consists of cardiac muscle cells

Function of the Heart

• The heart maintains an adequate and steady supply of nutrients to all organs and tissues
• The heart facilitates the removal of waste products from all organs and tissues
• Cardiac myocytes provide the force of contraction
• The conduction system and the nervous system control the flow and volume of blood

Dysfunction of the Heart

• Pump failure: weak contractility and emptying of chambers, impaired filling of chambers
• Obstruction to forward blood flow: valvular stenosis, vascular narrowing, systemic or pulmonary hypertension
• Regurgitant blood flow: volume overload of chamber behind failing affected valve
• Shunted blood flows from congenital defects: septal defects in heart, shunts between blood vessels
• Rupture of the heart or a major vessel: cardiac tamponade, massive internal hemorrhage
• Cardiac conduction disorders (arrhythmias): failure of synchronized cardiac contraction

Pathology of the Cardiovascular System

• Portals of entry: pericardium, hematogenous dissemination, foreign body penetration, direct extension from pleura or mediastinum
• Cardiac tamponade: compression of the heart caused by accumulation of blood in the pericardial sac, leading to reduced cardiac output and poor perfusion of vascular beds
• Hydropericardium: accumulation of clear, light yellow, watery, serous fluid in the pericardial sac
• Epicardial calcification: seen in hereditary calcinosis in mice, cardiomyopathy in hamsters, vitamin E-selenium deficiency in sheep and cattle, and vitamin D toxicity in several species

Other Conditions

• Gout: visceral gout occurs in birds and reptiles, characterized by white urate deposits on the epicardial surface
• Pericarditis: thrombosis or embolism of the coronary arteries can result in myocardial infarction and cardiac failure
• Lymphangitis: inflammation of the lymphatic vessels, caused by bacterial, mycotic, or parasitic infections