Circulatory Pathways

The sequence of events, which take place during the completion of one heart beat is called cardiac cycle. The duration of cardiac cycle is about 0.8 second.

Blood pressure is the pressure of blood against the walls of the main arteries. Pressure is highest during systole, when the ventricles are contracting (systolic pressure), and lowest during diastole, when the ventricles are relaxing and refilling (diastolic pressure). Blood pressure is measured in millimetres of mercury by means of a sphygmomanometer at the brachial artery of the arm, where the pressure is most similar to that of blood leaving the heart. The normal range varies with age, but a young adult would be expected to have a systolic pressure of around 120 mmHg and a diastolic pressure of 80 mmHg. So, the difference between systolic and diastolic pressure is 120 mm Hg - 80 mmHg = 40 mmHg

SA node is a pacemaker of the heart. It is a small mass of specialised muscle cells in the mammalian heart, found in the wall of the right atrium near the opening for the vena cava. The cells initiate and maintain the heart beat.