Circulatory System

• The location of the heart is in the mediastinum, surrounded by the anterior sternum, the posterior vertebral column and laterally by lungs, with the apex being the tip of the left ventricle and the base being the posterior surface.
• The pericardium is a double-layered serous membrane enclosing the heart and the major blood vessels that attach to the heart.
• The inner layer of the pericardium, also known as the visceral pericardium, is firmly attached to the surface of the heart.
• The fibrous pericardium is a tough, inelastic, dense irregular connective tissue that functions to prevent overstretching, for protection of the heart, and anchorage of the heart in the position.
• The outer layer of the pericardium, also known as the parietal pericardium, consists of the fibrous pericardium (thick) and the serous pericardium (thin).
• The base of the heart is the posterior surface.
• The apex of the heart is the tip of the left ventricle.
• The pericardium consists of three layers: the epicardium, the myocardium, and the endocardium.
• The epicardium, also known as the visceral layer of the pericardium, functions as a protective layer.
• Systemic Circulation is the blood flow from heart to body systems.
• Coronary Circulation is the blood supply to the heart, especially to the myocardium, and begins at the base of the ascending aorta.
• The conduction pathway consists of the sinoatrial (SA) node, atrioventricular (AV) node, atrioventricular (AV) bundle, and His-Purkinje system.
• Pulmonary Circulation is the blood flow from heart to lungs.
• Coronary (cardiac) veins parallel the arteries, collect deoxygenated blood, and empty into the right atrium.
• Nerve impulses from the autonomic nervous system (ANS) and hormones modify the timing and strength of each heartbeat.
• The Refractory period is the time interval during which the second contraction cannot be triggered and lasts longer than the contraction itself.
• The non-SA nodal autorhythmic tissues are latent pacemakers.
• The main phases of an action potential are Depolarization, Plateau, Repolarization, and Refractory period.
• Action potential in contractile cells is initiated by the SA node and spreads out to excite "working" fibers called contractile fibers.
• The myocardium, which is relatively thick and consists largely of the cardiac muscle tissue, functions as a forcing the blood out of the heart chambers.
• The endocardium, which consists of epithelium and connective tissue (elastic and collagenous fibers), is continuous with the inner linings of the blood vessels attached to the heart.
• The heart valves include atrioventricular (AV) valves such as the tricuspid valve and bicuspid/mitral valve, and semilunar (SL) valves like the aortic semilunar valve and pulmonary semilunar valve.
• Papillary muscles are muscular projections of the inner ventricular wall.
• The conduction system of the heart is formed by groups of autorhythmic cells in a few regions of the heart and undergoes spontaneous excitation and rapid conduction of action potentials.
• The right ventricle discharges to the pulmonary trunk.
• Autorhythmic cells are the specialized cardiac muscle fibers that repeatedly generate action potentials that trigger heart contractions.
• The conduction system consists of the sinoatrial (SA) node, atrioventricular (AV) node, atrioventricular bundle, right & left bundle branches, and Purkinje fibers.
• The right atrium receives from the vena cava & coronary sinus.
• The function of chordae tendineae is to help anchor the AV valve flaps in their closed position to prevent backflow of blood into atria during ventricular contraction.
• If the SA node fails to fire, then the AV node will take over.
• The two important features of cardiac muscle are the existence of gap junctions between cardiac muscle cells and the existence of the conducting system.
• The two important functions of autoryhthmic cells are to act as a pacemaker, the SA node, and to form the conduction system.
• The left atrium receives from the pulmonary veins.
• The SA node acts as the natural pacemaker and is faster than other autorhythmic fibers.
• The left ventricle discharges to the aorta.
• The heart consists of the right and left atria, which are receiving chambers and small and thin-walled, and the right and left ventricles, which are discharging chambers and big and thick-walled.