The cardiovascular system is divided into two circuits. The Heart. The Heart. The Heart

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1 The cardiovascular system is divided into two circuits The Heart Chapter 20 Pulmonary circuit Carries blood to and from the lungs Systemic circuit Carries blood to and from the rest of the body Vessels carry the blood through the circuits Arteries carry blood away from the heart Veins carry blood to the heart Capillaries permit gas, nutrient, and waste, transfer The Heart Despite its impressive workload, the heart is a small organ, roughly the size of a clenched fist The heart has four chambers, two associated with each circuit The right atrium receives blood from the systemic circuit and passes it to the right ventricle, which pumps blood to the pulmonary circuit The left atrium receives blood from the pulmonary circuit and passes it to the left ventricle, which pumps blood to the systemic circuit The Heart The heart is located in the anterior chest wall directly posterior to the sternum The heart is surrounded by the pericardial cavity, which is lined with the pericardium The pericardium is lined with a serous membrane which can be subdivided into the visceral pericardium and parietal pericardium The visceral pericardium, or epicardium, covers and adheres closely to the surface of the heart The parietal pericardium lines the inner surface of the pericardial sac, or fibrous pericardium, which stabilizes the position of the heart 1

2 Superficial Anatomy of the Heart The four chambers of the heart are two atria and two ventricles The coronary sulcus is a deep groove that marks the border between the atria and ventricles The anterior interventricular sulcus and posterior interventricular sulcus, mark the boundary between the left and right ventricles The Heart Wall Components of the heart wall include The epicardium, the visceral pericardium that covers the surface of the heart The myocardium, the muscular wall of the heart, which forms both the atria and ventricles, and also contains blood vessels and nerves The endocardium, a layer of simple squamous epithelium, that lines the inner surface of the heart, including the valves Internal Anatomy The atria are separated by the interatrial septum, the ventricles separated by the interventricular septum The atrioventricular (AV) valves are folds of fibrous tissue that permit blood flow in only one direction, from the atria to the ventricles 2

3 The Right Atrium The right atrium receives blood from the systemic circuit via the superior vena cava and inferior vena cava The superior vena cava carries blood from the head, neck, upper limbs, and chest The inferior vena cava carries blood from the rest of the body The coronary veins of the heart return blood to the heart via the coronary sinus The Right Ventricle Blood travels from the right atrium to the right ventricle through the right AV or tricuspid valve The free edges of the fibrous flaps of the valve are attached to the ventricular wall by the chordae tendineae, which prevent the flaps of the valve from swinging into the atrium when the ventricle contracts The superior end of the right ventricle tapers to the conus arteriosus and ends at the pulmonary semilunar valve From the right ventricle blood flows into the pulmonary trunk The Left Atrium Blood returns from the lungs via the left and right pulmonary veins and enters the left atrium From the left atrium blood passes into the left ventricle via the left AV, bicuspid, or mitral valve The Left Ventricle Despite the fact that their blood volumes are equal, the left ventricle is much larger than the right The thick muscular walls of the left ventricle account for this size difference and enable the left ventricle to develop sufficient pressure to push blood through the systemic circuit Blood leaves the left ventricle through the aortic semilunar valve and flows into the ascending aorta 3

4 Connective Tissues & The Fibrous Skeleton of The Heart Connective tissue fibers of the heart Provide physical support and elasticity Distribute the force of contraction Prevent overexpansion The fibrous skeleton Stabilizes the heart valves Physically isolates atrial from ventricular cells Musculature of the Heart Blood Supply to the Heart The coronary circulation supplies blood to the tissues of the heart Arteries include the right and left coronary arteries, marginal arteries, anterior and posterior interventricular arteries, and the circumflex artery Veins include the great cardiac vein, anterior and posterior cardiac veins, the middle cardiac vein, and the small cardiac vein 4

5 The Heartbeat Two types of cardiac muscle cells are involved in the normal heartbeat Cells of the conducting system control and coordinate the heartbeat Contractile cells produce powerful contractions that propel the blood The Conducting System The conducting system is responsible for initiating and distributing the stimulus to contract It includes: The sinoatrial i l(sa) node The atrioventricular (AV) node Conducting cells Atrial conducting cells are found in internodal pathways Ventricular conducting cells consist of the AV bundle, bundle branches, and Purkinje fibers 5

6 Impulse Conduction through the heart Cells in the SA node spontaneously depolarize more rapidly than other cells of the conducting system and thus begin the action potential The stimulus spreads to the AV node where it is delayed briefly The impulse then travels through ventricular conducting cells and is distributed by Purkinje fibers The electrocardiogram (ECG or EKG) An EKG is a recording of the electrical events occurring during the cardiac cycle The EKG shows several important features A P wave accompanies the depolarization of the atria The QRS complex appears as the ventricles depolarize and contract The T wave indicates ventricular repolarization Contractile Cells The Purkinje fibers distribute the stimulus to the contractile cells, which form the bulk of the atrial and ventricular walls Like skeletal muscle, the action potential leads to the release of Ca 2+ and the binding of Ca 2+ to troponin initiates the contraction The contraction is of considerably longer duration in cardiac muscle and called Plateau 6

7 The Cardiac Cycle The Cardiac Cycle is the period between the start of one heartbeat and the beginning of the next During each cardiac cycle Each heart chamber goes through systole (contraction) and diastole (relaxation) Correct pressure relationships are dependent on the careful timing of contractions Heart sounds Auscultation listening to heart sound via stethoscope There are four heart sounds S 1 lubb caused by the closing of the AV valves S 2 dupp caused by the closing of the semilunar valves S 3 a faint sound associated with blood flowing into the ventricles S 4 another faint sound associated with atrial contraction Stroke Volume and Cardiac Output Cardiac output the amount of blood pumped by each ventricle in one minute Cardiac output equals heart rate times stroke volume When needed HR can increase by 250% and SV can double CO Cardiac output (ml/min) = HR Heart rate (beats/min) X SV Stroke volume (ml/beat) 7

8 Factors Affecting Cardiac Output Factors Affecting Cardiac Output Exercise and Cardiac Output Heavy exercise can increase output by percent Trained athletes may increase cardiac output by 700 percent Cardiac reserve The difference between resting and maximal cardiac output 8