CARDIOVASCULAR SYSTEM Heart is enclosed by a membrane (pericardium) Wall of Heart: Epicardium: visceral pericardium = protection by reducing friction Myocardium: cardiac muscle Endocardium: inner layer of epithelium & elastic and collagenous connective tissue The heart has 4 chambers top = atria (right and left) bottom = ventricles (right, left) Ear-like projections = auricles Right & left side separated by the septum.

Atrioventricular (AV) valves Right side tricuspid valve-3 cusps Left side bicuspid valve-2 cusps The cusps of the valves are attached to strong fibrous strings (chordae tendinae) that prevent cusps from swinging back into the atrium. The valves only allow blood to flow in one direction (atrium to ventricle). The right ventricle has a thinner wall- pumps blood to the lungs The left ventricle has thicker walls because it must pump blood to the entire body. Heart sounds-lubb- AV valves close. Ventricles contract dubb-pulmonary & aortic valves close. Ventricles relax. Normal and abnormal EKGs and heart sounds

Right Side-blood low in oxygen returns to the heart via superior & inferior vena cava. As the right atrium relaxes, a vacuum is created, drawing in venous blood. The right atrium contracts, forcing blood through the tricuspid valve into the right ventricle. The ventricle contracts closing the tricuspid valve & blood is sent through the pulmonary valve into the pulmonary arteries, where it is carried to the lungs to eliminate CO 2 and pick up fresh O 2. Left Side-oxygenated blood enters the heart on the left side through the pulmonary veins. The left atrium contracts, forcing blood through the bicuspid valve into the left ventricle. The left ventricle contracts, closing the bicuspid valve and opening the aortic valve into the aorta.

Cardiac Conduction System SA Node (sinoatrial node) – special cardiac tissue near opening of the superior vena cava. It is responsible for the rhythmic activity of the heart by initiating an impulse that spreads into the myocardium and stimulates contraction. The SA node is called the pacemaker, initiating impulses per minute. AV Node (atrioventricular node)- located in the inferior portion of the upper septum. Impulses flow slowly through fibers from the SA node to the AV node, then quickly through the AV bundle. AV Bundle – large bundle of fibers whose branches give rise to purkinje fibers which spread down the septum to the base of the heart, then upward through the lateral walls of the heart. This causes the heart to contract from the bottom upward, forcing blood into the aorta and pulmonary arteries.

Vascular System– blood vessels 1. Arteries – strong, elastic walls adapted for carrying blood at high pressure. Arteries sub- divide into thinner vessels called arterioles. The inside layer is the endothelium which is a smooth surface to prevent blood clotting. It secretes substances that dilate and contract blood vessels. Arteries carry blood away from the heart. 2. Capillaries – smallest blood vessels. They connect arterioles and venules. They have thin walls, allowing substances in blood & tissue to be exchanged. Capillaries carry blood with high levels of O 2 & nutrients.

3. Veins – carry blood back to the heart. Path parallels the arteries. Veins have thinner walls and less elastic tissue than arteries. Veins have valves which keep blood flowing toward the heart. Veins subdivide into venules which can’t carry high pressure blood. Blood Pressure : is the force of blood against the inner walls of the blood vessels. During contraction of ventricles, arterial pressure (systolic pressure) is the highest. During ventricle relaxation, arterial pressure (diastolic pressure) is the lowest. Normal blood pressure is below 120/ /80 to 140/90 is prehypertensive. Normal heart rate is about 72 beats per minute. Blood pressure depends on: 1. Blood volume (5 L in adults) 2. Blood viscosity (ease of flow) 3. Resistance to flow (friction between blood and vessel walls 4. Stroke volume-volume of blood discharged from left ventricle with each contraction.