I. LOCATION OF THE HEART
The heart is located in the chest between the lungs behind the sternum and above the diaphragm. It is surrounded by the pericardium. Its size is about that of a fist, and its weight is about 250-300 g. Its center is located about 1.5 cm to the left of the midsagittal plane. Located above the heart are the great vessels: the superior and inferior vena cava, the pulmonary artery and vein, as well as the aorta. The aortic arch lies behind the heart. The esophagus and the spine lie further behind the heart.
II. FUNCTIONS OF THE HEART
The role of circulation is to:
1. Continuously deliver oxygen, nutrients, hormones, and antibodies to organs, tissues and cells throughout the body in response to varying tissue demands. 2. Remove end products of metabolism from tissue and cells. The role of the heart is to:
1. Pump oxygenated blood into the arterial system, where it is carried to the capillaries supplying tissues. 2. Collect oxygenated-poor blood from the venous system and pump it through the lungs to be re-oxygenated. The role of the blood vessel (arteries, capillaries, veins) is to carry blood to and from the bodies, tissues and cells.
III. ANATOMY OF THE HEART
The walls of the heart are composed of cardiac muscle, called myocardium. It also has striations similar to skeletal muscle. It consists of four compartments: the right and left atria and ventricles. The heart is oriented so that the anterior aspect is the right ventricle while the posterior aspect shows the left atrium. The atria form one unit and the ventricles another. The left ventricular free wall and the septum are much thicker than the right ventricular wall. This is logical since the left ventricle pumps blood to the systemic circulation, where the pressure is considerably higher than for the pulmonary circulation, which arises from right ventricular outflow. The heart has four valves. Between the right atrium and ventricle lies the tricuspid valve, and between the left atrium and ventricle is the mitral valve. The pulmonary valve lies between the right ventricle and the pulmonary artery, while the aortic valve lies in the outflow tract of the left ventricle (controlling flow to the aorta).
THE ANATOMY OF THE HEART AND ASSOCIATED VESSELS
Blood from the body returns to the right atrium through two large veins, the superior and inferior venae cavae; in addition the blood that has supplied the heart muscle is drained directly into the right atrium through the coronary sinus. Return of venous blood to the right atrium takes place during the entire heart cycle of contraction and relaxation, and to the right ventricle only during the relaxation part of the cycle, called diastole, when both right heart cavities constitute a common chamber; near the end of diastole, contraction of the right atrium completes the filling of the right ventricle with blood. Rhythmic contractions of the right ventricle expel the blood through the pulmonary arteries into the capillaries of the lung, where the blood receives oxygen. The lung capillaries then empty into the pulmonary veins, which in turn empty into the left atrium. Pulmonary venous return to the left atrium and left ventricle proceeds simultaneously in the same manner as the venous return to the right heart cavities. Contraction of the left ventricle rhythmically propels the blood into the aorta and from there to all arteries of the body, including the coronary arteries, which supply the heart muscle.
V. ELECTROPHYSIOLOGIC PROPERTIES OF THE HEART
Seven special properties of cardiac muscle are necessary for regulation of heart rate and rhythm. 1. Rhythmycity – rhythm in both the formation and conduction of electrical impulses from atria to ventricles. The heart beats with definite rhythm base on four phases: (a.)stimulation (b)transmission (c)contraction and (d)relaxation. Each contraction is accompanied...