The Cardiovascular System A&P Chapter 11 The cardiovascular system is the body’s way of transporting substances such as oxygen & nutrients using blood as a vehicle. The force to move the blood around the body is provided by the beating heart The blood vessels are the network of tubes through which the blood is moved.

The Heart The heart is approximately the size of a person’s fist. It is hollow and cone-shaped, typically weighing less than one pound. It is enclosed by the middle cavity of the thorax (mediastinum) and flanked by the lungs on each side. It’s apex (pointed end) is directed toward the left hip and rests on the diaphragm. The base points towards the right shoulder & lies beneath the second rib.

Coverings of the Heart The heart is enclosed by a double sac of serous membrane called the pericardium. The pericardium consists of several parts: Epicardium or visceral pericardium – tightly encloses external surface of heart Parietal pericardium – joins loosely with epicardium at base of heart Fibrous pericardium – protects heart and anchors it to surrounding structures The serous membrane produces a slippery lubricant that allows the heart to beat without friction.

The Walls of the Heart The heart walls are composed of three layers: Outer epicardium: composed of the visceral pericardium Myocardium: consists of thick bundles of cardiac muscle twisted and whorled into ring-like arrangements, reinforced by a dense, fibrous connective tissue The layer that actually contract Endocardium: Thin sheet of endothelium that lines the heart chambers and is continuous with blood vessels entering and leaving the heart

Layers of the Heart Tissue

Chambers of the Heart The heart has four hollow cavities or chambers, lined with endocardium which helps the blood flow smoothly. Two Atria: Superior Receiving chambers Do not help with pumping Two Ventricles: Inferior and thick-walled Discharging chambers Contractions pump blood out of heart

Separation of the Heart The right ventricle forms the anterior surface of the heart. The left ventricle forms the apex of the heart. The septum that divides the heart longitudinally.

Pulmonary Circulation The right side of the heart functions as the pulmonary circuit pump. Steps of Pulmonary Circulation: 1.) Right atria receives oxygen-poor blood from the body through the superior & inferior venae cavae. 2.) Right ventricle pumps blood out through the pulmonary trunk which splits into the pulmonary arteries which carry the blood to the lungs. 3.) In the lungs the blood releases CO2 and picks up oxygen to return to the left side of the heart.

Systemic Circulation The left side is the pump for systemic circulation which supplies oxygen-rich blood to the body. Steps of systemic circulation: 1.) Blood from the lungs enters the left atria. 2.) Left ventricle pumps blood out the aorta which branches into arteries carrying blood to all tissues of the body. 3.) Systemic veins gather oxygen-poor blood from tissues of the body and it flows back into either the superior or inferior vena cava. Left ventricle has thicker walls & is a stronger pump due to greater distance it must pump blood.

Heart Valves The heart is equipped with four valves which allow blood to flow in only one direction through the chambers. Two atrioventricular or AV valves Flow between atria and ventricles Two semilunar valves Flow from ventricles out large arteries leaving the heart

AV Valves The AV valves prevent backflow into the atria when the ventricles contract. The left AV valve or bicuspid valve consists of two flaps or cusps of endocardium. The right AV valve or tricuspid has three flaps. Tiny, white cords called chordae tendineae anchor the flaps to the walls of the ventricle and work to close the valve during a contraction.

Semilunar Valves Semilunar valves guard against backflow into the ventricles from the major arteries. Each has three leaflets that close the valve after the ventricular contraction. AV valves are open when the heart is relaxed and semilunar valves are closed. AV valves close when the heart contracts and semilunar valves are open. A leaky valve can cause the heart to work harder because it is pumping the blood more than once.

Cardiac Circulation The blood supply that oxygenates the heart is provided by the right and left coronary arteries. The coronary arteries branch off of the aorta. The coronary arteries are compressed when the ventricles are contracting and fill when the heart is relaxed. The myocardium is drained by cardiac veins into the coronary sinus which empties into the right atrium.

Physiology of the Heart The heart circulates the 6 L of blood in the body about 1000 times a day. Cardiac muscle cells contract spontaneously and independently of nerve impulses. Cardiac contractions are regular and continuous, however the different areas of the heart contract with different rhythms.

Regulating Heart Activity Two systems act to regulate heart activity: Autonomic nervous system acts to accelerate or slow down the heart in response to stimulus. Intrinsic Conduction System or nodal system is built into the heart and sets its normal rhythm. Composed of special tissue that is a cross between muscle and nervous tissue. Causes heart to depolarize in only one direction from atria to ventricles.

Intrinsic Conduction System The intrinsic conduction system consists of several parts: Sinoatrial or (SA) node: right atrium Atrioventricular (AV) node: junction of atria and ventricles Atrioventricular (AV) bundle: located in the interventricular septum Bundle bunches: interventricular septum Purkinje fibers: muscle of ventricle walls

Action of the ICS The SA node starts each heartbeat and sets the pace for the entire heart. (1) The impulse spreads through the atria to the AV node, and then the atria contract. (2) The impulse is delayed & then passed through the AV bundle, bundle branches &Purkinje fibers in a motion that “wrings out” the ventricles from the apex towards the atria.

Problems with the Heart Rate Damage to the AV node can result in a slow or uneven heart rate. Fibrillation is a rapid, uncoordinated shuddering of the heart caused by inadequate supply of blood to heart muscle. Tachycardia is a rapid heart rate, over 100 beats per minute. Bradycardia is a slow heart rate, less than 60 beats per minute.