The Circulatory System The Heart and Blood Vessels

The Circulatory System “The Heart and Blood Vessels”

Location of the Heart • The heart is a 4 chambered muscle that pumps blood through a closed circulatory system • 2/3 of the heart lies to the left of the midline of the body • The apex lies on the diaphragm and the upper border (base) just below the second rib

Anterior View

Posterior View

Coverings of the Heart Pericardium is the tough sac that surrounds the heart. • Fibrous pericardium- tough inelastic sac around the heart. • Serous pericardium-consists of parietal layer (outside) and visceral layer (touches the heart). • Pericardial space is filled with lubricating (pericardial) fluid.

3 Layers of the Heart • Epicardium- same as the visceral layer of the pericardium • Myocardium- thick contractile cardiac muscle cells. The cells are tightly joined together to form a syncytium which transmits action potentials seamlessly. • Endocardium- thin layer that covers muscular projections called trabeculae. This tissue’s folds make up the valves. It is also continuous with lining of blood vessels.

Chambers of the Heart Septum separates the chambers Atria- two upper chambers of heart - “receiving chambers” Veins carry blood into the atria Ventricles- two lower chambers which have very thick myocardial “pumping chambers”

Valves of the Heart Valves permit blood flow in only one direction. Atrioventricular (cuspid valves) are anchored to papillary muscles through chordae tendineae – Tricuspid valve has three flaps of endothelium and connects right atrium and ventricle – Bicuspid valve (mitral valve) has two flaps and connects left atrium and ventricle Semilunar Valves have half-moon shaped flaps growing out of lining of blood vessels. – Pulmonary semilunar valve – Aortic semilunar valve

Blood Flow Through the Heart Arteries always carry blood away from heart Veins always carry blood toward the heart • • • • Superior and inferior vena cavae Right atrium Tricuspid valve Right ventricle Semilunar pulmonary valve Pulmonary arteries Lungs Pulmonary veins Left atrium Mitral valve Left ventricle Aortic semilunar valve Aorta to the rest of the body

Blood Supply to the Heart Coronary Arteries branch off directly from the aorta. They can form anastomoses to ensure blood flow. Coronary Veins drain blood into the right atrium through the coronary sinus.

Heart Disorders Myocardial infarction (heart attack) – when coronary arteries are clogged (by a clot or plaque) and cardiac cells are starved of oxygen (ischemia). Mitral valve prolapse – mitral valve (bicuspid) flaps extend into atrium causing leaking