Anatomy II - The Heart (I) PDF

The Heart (I) DR. MARIE P. AFFANA, M.D ALL SAINTS UNIVERSITY SCHOOL OF MEDICINE INTRO TO ANATOMY II PREMED 2 Position  Lies within the pericardium in middle mediastinum...

The Heart (I) DR. MARIE P. AFFANA, M.D ALL SAINTS UNIVERSITY SCHOOL OF MEDICINE INTRO TO ANATOMY II PREMED 2 Position  Lies within the pericardium in middle mediastinum  Behind the body of sternum and the 2nd to 6th costal cartilages  In front of the 5th to 8th thoracic vertebrae  A third of it lies to the right of median plane and 2/3 to the left  Anterior to the vertebral column, posterior to the sternum EXTERNAL CHARACTERISTICS  A hollow muscular organ, pyramidal in shape , somewhat larger than a closed fist; consists of four chambers (right and left atria, right and left ventricles)  Cardiac Apex is formed by left ventricle and is directed downwards and forwards to the left.  It lies at the level of the fifth left intercostal space, 1~2cm medial to the left midclavicular line (9cm from the midline) EXTERNAL CHARACTERISTICS  The apex beat 【 point of maximum impulse (PMI) 】 , is the furthermost point outwards (laterally) and downwards (inferiorly) from the sternum at which the cardiac impulse can be felt.  Lateral and/or inferior displacement of the apex beat usually indicates enlargement of the heart, called cardiomegaly  Cardiac base is formed by the left atrium and to a small extent by the right atrium. It faces backward, upward and to the right  In its typical anatomical orientation, the heart has 5 surfaces, formed by different internal divisions of the heart:  Anterior (or sternocostal) – Right ventricle.  Posterior (or base) – Left atrium.  Inferior (or diaphragmatic) – Left and right ventricles.  Right pulmonary – Right atrium.  Left pulmonary – Left ventricle. Borders of the heart  Separating the surfaces of the heart are its borders. There are four main borders of the heart:  Right border – Right atrium  Inferior border – Left ventricle and right ventricle  Left border – Left ventricle (and some of the left atrium)  Superior border – Right and left atrium and the great vessels Grooves of the heart  Coronary sulcus (circular sulcus) which marks the division between atria and ventricles, contains the trunks of the coronary vessels and completely encircles the heart  Interatrial groove － separates the two atria and is hidden by pulmonary trunk and aorta in front  Interventricular grooves － anterior and posterior, mark the division between ventricles (which separates the RV from the LV), the two grooves extend from the base of the ventricular portion to a notch called: the cardiac apical incisure The Heart Wall The heart wall itself can be divided into three distinct layers: Endocardium Myocardium Epicardium Endocardium  The innermost layer of the cardiac wall  Lines the cavities and valves of the heart.  Comprised of loose connective tissue and simple squamous epithelial tissue – it is similar in its composition to the endothelium which lines the inside of blood vessels.  In addition to lining the inside of the heart, the endocardium also regulates contractions and aids cardiac embryological development. Subendothelial layer  Lies between, and joins, the endocardium and the myocardium.  Consists of a layer of loose fibrous tissue, containing the vessels and nerves of the conducting system of the heart.  The purkinje fibres are located in this layer.  Damage to this layer can result in various arrhythmias. Myocardium  Composed of cardiac muscle and is an involuntary striated muscle.  The myocardium is responsible for contractions of the heart. Subepicardial Layer  The subepicardial layer lies between, and joins, the myocardium and the epicardium. Epicardium  Outermost layer of the heart, formed by the visceral layer of the Pericardium.  Composed of connective tissue and fat.  Connective tissue secretes a small amount of lubricating fluid into the pericardial cavity.  In addition to the connective tissue and fat, the epicardium is lined by on its outer surface by simple squamous epithelial cells. The pericardium The Pericardium  the pericardium is a fibroserous, fluid filled sack that surrounds the muscular body of the heart and the roots of the great vessels (the aorta, pulmonary artery, pulmonary vein and the superior and inferior vena cava). The Pericardium - Functions  Fixes the heart in the mediastinum and limits its motion – this is due to its attachment to the diaphragm, the sternum and the tunica adventitia (outer layer) of the great vessels  Prevents overfilling of the heart – The relatively inextensible fibrous layer of the pericardium prevents the heart from increasing in size too rapidly, thus placing a physical limit on the potential size of the organ  Lubrication – A thin film of fluid between the two layers of the serous pericardium reduces the friction generated by the heart as it moves within the thoracic cavity  Protection from infection – The fibrous pericardium serves as a physical barrier between the muscular body of the heart and adjacent organs prone to infection, such as the lungs. The Pericardium – Anatomical Structure  Thepericardium is made up of two main layers  Fibrouspericardium: a tough external layer  Serous Pericardium: a thin, internal layer Fibrous Pericardium  Continuous with the central tendon of the diaphragm  Made of tough connective tissue and is relatively non-distensible.  This rigidity prevents rapid overfilling of the heart, but can have several serious clinical consequences (cardiac tamponade)  Serous Pericardium  Divided into two layers  the outer parietal layer which lines the internal surface of the fibrous pericardium  Internal visceral layer which forms the outer layer of the heart (also known as the epicardium).  Each layer is made up of a single sheet of epithelial cells, known as mesothelium.  Found between the outer and inner serous layers, is the pericardial cavity, which contains a small amount of lubricating serous fluid.  This fluid serves to minimize the friction generated by the heart as it contracts and moves about within the thoracic cavity. Beck's triad The triad describes the classic findings in cardiac tamponade: Hypotension Jugular venous distension Muffled heart sounds on auscultation Also Pulsus paradoxus: a drop in systolic blood pressure of > 10 mm Hg during inspiration Pericardiocentesis  A needle is inserted into the pericardial space.  Fluid is removed to relieve pressure on the heart.  A catheter can be placed for periodic drainage. Subxiphoid approach for pericardiocentesis: This approach allows the drainage of pericardial fluid. An 80-year-old man presents to the emergency department for gnawing substernal chest pain that radiates to his neck and left arm. A 12-lead electrocardiogram (ECG) is obtained and shows an ST-elevation myocardial infarction. He is admitted for treatment and his symptoms resolve, but on day four of his hospitalization, he suddenly develops chest pain and shortness of breath. Blood pressure is 70/40 mm Hg, respiratory rate is 28/min, and pulse is 110/min. Physical examination shows jugular venous distention (JVD), distant heart sounds, and clear lung fields on auscultation. There is no peripheral edema. What is the most likely cause of this man’s condition? A. Right heart failure B. Ventricular fibrillation C. Cardiac tamponade D. Pericarditis E. Posterior papillary muscle rupture Chambers of the heart Atria  Receiving chambers of the heart  Receive venous blood returning to heart  Pump blood into ventricles  Separated by an interatrial septum (wall)  Foramen ovale - opening in interatrial septum in fetus  Fossa ovalis - remnant of foramen ovale  Each atrium has a protruding auricle  Pectinate muscles mark atrial walls  Blood enters right atria from superior and inferior venae cavae and coronary sinus  Blood enters left atria from pulmonary veins Left atrium  Left auricle － projecting to the right, pectinate muscles in wall  Four inlets － four orifices of pulmonary veins open through the posterior wall  One outlet － left atrioventricular orifice, blood leaves through left atrioventricular orifice to left ventricle Ventricles  Discharging chambers of the heart  Separated by an interventricular septum  Papillary muscles and trabeculae carneae muscles mark ventricular walls  Contains components of the conduction system  Right ventricle pumps blood into the pulmonary trunk  Left ventricle pumps blood into the aorta  Thicker myocardium due to greater work load Left Ventricle  It’s wall is three times thicker than that of right ventricle  One inlet － left atrioventricular orifice  One outlet － aortic orifice