Listen to the apical heart rate at this location.
SLIDE 3 Contraction of the Heart to Pump Blood The heart's pumping action is sparked by specialized pacemaker cells and conduction fibers that initiate spontaneous electrical activity, causing muscle contractions that result in a heartbeat. The conduction pathways are located in the myocardium and transmit the electrical impulse throughout the heart. The sinoatrial (SA) node is located in the right atrium and is called the “pacemaker” of the heart because it normally initiates the electrical impulses. The atrioventricular (AV) node (or junction) is located in the lower part of the right atrium. It relays the impulse from the SA node to the bundle of His and throughout the ventricles via the Purkinje fibers. The heart rate and rhythm are influenced by the autonomic nervous system; factors affecting the autonomic nervous system can speed up or slow down
the heart rate. SLIDE 4 The Cardiac Cycle The cardiac cycle consists of contraction of the muscle (systole) and relaxation of the muscle (diastole). The heart pumps out about 5 L of blood every minute. The amount of cardiac output depends on the heart rate, the amount of blood returning to the heart (venous return or preload), the strength of contraction, and the resistance to the ejection of the blood (afterload). Stroke volume equals the amount of blood ejected by a ventricle during one contraction. Cardiac output equals stroke volume multiplied by the heart rate. SLIDE 8 Blood Flow Throughout the Body
Three types of blood vessels make up the vascular system: arteries veins, capillaries These vessels conduct the blood from the body tissues to the heart –lung circulation and from the heart back to the tissues. Arteries carry oxygenated blood away from the heart Veins carry oxygen-depleted blood back to the heart for reoxygenation by the lungs Small veins, venules, and small arteries, arterioles, are connected by the capillaries. It is in the capillaries that the oxygen is transported to cells and waste products are removed from them The aorta is the largest artery in the body, and it receives blood from the left
ventricle. The inferior and superior vena cava are the largest veins in the body and empty blood into the right atrium of the heart. Arteries are elastic and accommodate changes in blood flow by constricting or dilating. Three layers of tissue make up the artery wall: The outer layer (the tunica adventitia) is connective tissue The middle layer (the tunica media) is smooth muscle; and the inner layer (the tunica intima) consists of endothelial cells. SLIDE 9 Veins have the same three layers but with less smooth muscle and connective tissue.
The veins are thinner and less rigid and thus can hold more blood. The heart pumps blood through the arterial system with each contraction.
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- Fall '17