• The heart is hollow organ. One septum divides the heart into two chambers. The left cardiac chamber discharges blood received from the pulmonary circulation. This blood is discharges out through the aorta to the systemic circulation. The right heart chamber discharges blood received from the systemic circulation. This blood is discharges to the lungs through the pulmonary arteries.
• Physiologists have determined that in the adult the heart makes from 60-72 beats per minute.
• Each beat of the heart is followed by a period of rest for the cardiac muscle. Each wave of contraction and a period of rest following it compose a cardiac cycle. a) Auricular systole b) Ventricular systole c) Joint diastole
• Each cardiac cycle consist of three phases: physiologists have called the first phase of short contraction of both atria- the atrial systole. The second phase of a more prolonged contraction a both ventricles-the ventricular systole. The period of rest of the cardiac muscle is called the diastole.
• This phase involves the contraction of the 2 auricles, pushing the blood into the respective ventricles. There is no back flow of blood due to the presence of the bicuspid and the tricuspid valves. The atrial systole takes 0.1 second. This is followed by the atrial diastole when both the auricles relax simultaneously. This is about 0.7 seconds.Auricular Systole (AtrialSystole)
• Ventricular systole is followed by ventricular diastole. The auricles are already in diastole, so all the chambers of the heart are in diastole.• When the ventricles are in diastole, the pressure in the ventricles decreases more than that in the great arteries. So to prevent the backward flow of blood, the semilunar valves close rapidly. This produces the second heart sound called dup.• During a complete cardiac diastole, blood from the superior and inferior vena cava flows into the auricles slowly. The pressure in the ventricles decreases and finally becomes lower than atrial pressure. Then the AV values open and blood from the atria starts entering into the relaxing ventricles. A complete cardiac diastole takes only 0.4 seconds.Joint Diastole.
• The left ventricle discharges out the blood received by the left atrium from the pulmonary circulation through the aorta to the systemic circulation.
• The blood received from the systemic circulation by the right atrium is discharged out of the right ventricle to the lungs through the pulmonary arteries.
Factors that affect theincidence of coronaryheart disease.