CHAPTER 7: CARDIOVASCULAR SYSTEM

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The heartbeat consists of phases: Systole refers to contraction of heart chambers and Diastole is relaxation of heart chambers. Atria contract first while ventricles relax (0.15 sec), then ventricles contract while atria relax (0.30 sec), then all chambers rest (0.40 sec). When the heart beats, the familiar lub-dup sound is heard as valves of the heart close. Lub is caused by vibrations occurring when the atrioventricular valves close due to ventricular contraction. Dup is heard when the semilunar valves close due to back pressure of blood in the arteries. A heart murmur is often due to ineffective valves, which allow blood to pass back into the atria after the atrioventricular valves have closed Rhythmical contraction of the atria and ventricles is due to the intrinsic conduction system of the heart. SA (Sinoatrial) node is found in the upper dorsal wall of the right atrium. It initiates the heartbeat by sending out an excitatory impulse every 0.85 seconds that cause atria to contract. It is called the pacemaker because it serves to keep the heartbeat regular. AV (Atrioventricular) node is found at the base of the right atrium very near the septum. When stimulated by impulses from SA node, it sends out impulses through septum to cause ventricles to contract. An electrocardiogram (ECG) is a recording of the electrical changes that occur in myocardium during a cardiac cycle. An abnormality called ventricular fibrillation can be detected using an ECG. Ventricular fibrillation is the most common cause of sudden cardiac death in seemingly healthy individuals over the age of 35. IV. Features of the Cardiovascular System A. Pulse Causes uncoordinated contraction of the ventricles. Can be caused by injury or drug overdose. The surge of blood entering the arteries causes their elastic walls to stretch and then recoil. This alternating stretching and recoiling of an arterial wall can be felt as a pulse in any artery that runs close to the body’s surface.
Pulse can be felt by placing several fingers on the radial artery which lies near the outer border of the palm side of a wrist. A carotid artery, on either side of the trachea in the neck, is another accessible location for feeling the pulse. Normally the pulse rate indicates the rate of heartbeat because the arterial walls pulse whenever the left ventricle contracts. B. Blood Flow The pulse rate is usually 60–80 beats per minute. Blood pressure is the pressure of blood against the wall of a blood vessel. A sphygmomanometer which has a pressure cuff is used to measure blood pressure in the brachial artery of the arm. Systolic pressure is the highest arterial pressure reached during ejection of blood from the heart. Diastolic pressure is the lowest arterial pressure that occurs while the heart ventricles are relaxing. Normal resting blood pressure for a young adult is 120mm mercury (Hg) over 80 mm Hg or 120/80. The higher number is the systolic pressure and the lower number is the diastolic pressure. Blood pressure varies throughout the body. It is highest in the aorta and lowest in the vena cava. Both systolic and diastolic pressure decrease with distance from the left ventricle. Blood pressure is minimal in venules and veins. Instead of blood pressure, venous return is dependent on skeletal muscle contraction, the presence of valves in veins, and respiratory movements. V. The Cardiovascular Pathways A. The cardiovascular system has 2 major circular pathways: The pulmonary circuit which circulates blood through the lungs and the systemic circuit which serves the needs of the body tissues. B. The Pulmonary Circuit Deoxygenated blood from the body collects in the right atrium and then passes into the right ventricle, which pumps it to pulmonary trunk.
Page 1 and 2: I. The Blood Vessels Chapter 5: Car
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CHAPTER 7: CARDIOVASCULAR SYSTEM

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