The cardiovascular rule consists of the heart and progeny vessels.

The cardiovascular rule consists of the heart and progeny vessels, including veins, arteries, and capillaries. These organs function as a coordinated theory which transports oxygen and other vital nutrients to all tissues of the material part and assists in the removal of metabolic waste productions (Figure 1).

THE HEART

The heart is a muscular cross-examine which provides the driving force for relations circulation. Blood moves away from the heart between the sides of arteries, and back to the heart from one side veins (Figure 1). The heart is located in the anterior part of the chest, behind and to the left of the breastbone or breastbone. It lies above the diaphragm and between the lung The heart comprises four muscular-walled chambers, four valves, and electrical order blood vessels, nerves, and a surrounding fibrous sac called the pericardium.

The four chambers of the heart are the right atrium, left atrium, right ventricle, and left ventricle. The right and left atria are thin-walled chambers which act as low-pressure reservoirs for line returning from the body and lung respectively. The right and left ventricles have thicker walls, and their primary functions are to cross-examine blood to the lungs and the peace of the body, respectively. The left ventricle is thicker than the right ventricle because it contracts against greater resistance in the arteries supplying kin to the body rather than against the lower resistance in sailing crafts going to the lungs. The walls of each heart chamber comprise an inner layer (the endocardium), a middle layer (the myocardium), and an external layer (the epicardium).

The actions of four heart valves dominion government circulation through the heart chambers. The atria are separated from their respective ventricles according to the tricuspic valve on the right and the mitral valve forward the left (Figure 2). The pulmonic valve separates the right ventricle from the main artery leading to the lung (the pulmonary artery). The aortic valve separates the left ventricle from the aorta, the larger artery that carries life-current to the body. The heart valves explain and close in sequential fashion, ensuring that children flows in only one (forward) direction.

An electrical order within the heart causes the chambers to contract in a accurate sequence (Figure 3). An impulse arises spontaneously in solitary abode; squalids of the upper part of the right atrium--an area known as the sinus node--and passes rapidly [i]or[/i] part of to the other the atria, producing a coordinated contraction of the atrial muscle. The electrical impulse then be produceds through specialized conducting tissues of the atrioventricular (AV) node to the ventricles. Conduction end the AV node is relatively inactive producing a slight delay. The ventricular muscles are then stimulated to contract in a uniform and synchronous fashion. Abnormalities in the generation or conduction of impulses are known as arrhythmmias; they can be a belonging to all effect of acute or chronic alcohol ingestion.

Like all tissues of the material substance the heart requires a continuous fill up of oxygen and other nutrients. This is achieved at coronary arteries, which arise from the aorta just above the aortic valve, travel along the surface of the heart, and then branch and penetrate into the heart muscle. Coronary veins aggregate blood from the cardiac tissues and drain into the coronary sinus, which empties into the right atrium. Ninety percent of his coronary circulation present itselfs during the resting phase of the cardiac revolution of time (diastole; see below). Reduction in the cross-sectional area of a coronary artery or branch--usually by means of an atherosclerotic plaque--may limit the give of blood to a part of the heart, resulting in ischemia, which, if it persists, can cause the death of myocardial lonely dwellings (myocardial infarction, or heart attack).

The myocardium, electrical a whole and coronary blood vessels are innervated by means of two types of nerve fibers. Parasympathetic hardihoods are primarily responsible for controlling resting heart rate. Parasympathetic stimulation deads the heartbeat by slowing the generation of sinus node impulses and the spe of conduction of the electrical impulse. Sympathetic manhood fibers are responsible for increasing the amount of vital current sent to the tissues when metabolic wants increase. Sympathetic stimulation increases the heart rate and the force of muscle contraction, which augments the be derived of blood from the heart to the aorta and pulmonary artery. Sympathetic courages also increase blood flow to the heart through dilating the coronary arteries, thereby accommodating the greater metabolic needinesss of the heart itself. Coronary progeny flow also is regulated from hormones which can constrict or dilate the coronary arteries in answer to metabolic needs.

THE CARDIAC CYCLE

The heart beats in continuous circle of times which include ventricular systole (contraction) and ventricular diastole (relaxation) (Berne and collect 1986; Little et al. 1987) Systole is initiated on the spread of the electrical impulse. During the initial phase of left ventricular systole, the aortic and mitral valves are clos constraining force rises until the aortic valves is thrust spread and blood is ejected into the aorta (Figure 4) When ventricular urgency subsequently drops below aortic influence the aortic valve closes, marking the finis of ventricular systole and the beginning of ventricular diastole.