The Anatomy of the Heart PDF

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The Anatomy of the Heart...

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The Anatomy of the Heart •

The heart is positioned obliquely between the lungs in the mediastinum. § About 2/3 of its bulk lies to the left side of the midline of the body.

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Shaped like a blunt cone. About the size of a closed fist. Approx. 5 in long (12 cm), 3.5 in wide at its broadest point (9 cm), and 2.5 in thick (6 cm).

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It is enclosed in a loose fitting serous membrane known as the pericardial sac (parietal pericardium). § Pericardial sac is made up of 2 layers: § The outermost layer is the fibrous layer or fibrous pericardium. § It is made of tough fibrous connective tissue and connects to the large blood vessels that enter and leave the heart, to the diaphragm muscle, and to the inside of the sternal wall of the thorax. § It prevents overdistention of the pumping heart by acting as a tough protective membrane surrounding the heart. § It also anchors the heart in the mediastinum. § The innermost layer is the serous layer or serous pericardium. § This layer is thin and delicate. § It is continuous with the outermost layer of the wall of the heart, called the epicardium, at the base of the heart. § It is also continuous with the large blood vessels of the heart and is also known as the parietal layer of the pericardial sac.

The Layers of the Heart Wall •

The outermost layer of the wall of the heart is called the epicardium or visceral pericardium. § It is a thin, transparent layer composed of serous tissue and mesothelium. § B/c of its serous nature, it can also be called the serous pericardium of the heart.

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Between the epicardium of the heart and the serous pericardium of the pericardial sac is a space called the pericardial cavity. § This cavity contains a watery fluid called the pericardial fluid, which reduces friction and erosion of tissue between these membranes as the heart expands and contracts during a cardiac cycle. § If an inflammation of the innermost layer of the pericardial sac develops, it is known as pericarditis.

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Underneath the epicardium is the second layer of the wall of the heart. § This makes up the bulk of the heart and is called the myocardium. § This is the layer of cardiac muscle tissue; its cells or fibers are involuntary, striated, and branched. § The tissue of this layer is arranged in interlacing bundles and is the layer responsible for contraction of the heart.

The Anatomy of the Heart •

The third or innermost layer of the wall of the heart is called the endocardium. § It is a thin layer of endothelium that overlies a thin layer of connective tissue penetrated by tiny blood vessels and bundles of smooth muscle. § It acts as a lining for the myocardium. § It covers the valves of the heart and the chordae tendineae of the valves.

The Chambers of the Heart •

The inside of the heart is divided into four chambers that receive blood from various parts of the body. § The 2 upper chambers are called the right atrium and the left atrium. § Each atrium has an external appendage called an auricle, named b/c of its similarity to the ear of a dog. § The auricle increases the volume of the atrium. § The lining of each atrium is smooth, except for the anterior atrial walls and the lining of the 2 auricles, which contain projecting muscle bundles called the musculi pectinati that give the auricles their rough appearance. § The 2 atria are separated from each other by an internal interatrial septum. § The lower 2 chambers are called the right ventricle and the left ventricle. § The 2 ventricles are separated from one another by an internal interventricular septum. § The irregular ridges and folds of the myocardium of the ventricles are called the trabeculae carneae.

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The muscle tissue of the atria and ventricles is separated by connective tissue that also forms the valves. § This connective tissue divides the myocardium into two separate muscle masses.

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Externally, a groove called the coronary sulcus separates the atria from the ventricles. Two other sulci are seen externally; the anterior interventricular sulcus and the posterior interventricular sulcus separate the right and left ventricles from one another. The sulci contain a varying amount of fat and coronary blood vessels (blood vessels that supply the heart tissue with blood).

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The Great Vessels of the Heart •

The right atrium receives blood from all parts of the body except the lungs. § It receives this blood through three veins: § The superior vena cava, a.k.a the anterior vena cava, brings blood from the upper parts of the body (head, neck, and arms). § The inferior vena cava, a.k.a the posterior vena cava, brings blood from the lower parts of the body (legs and abdomen). § The coronary sinus drains the blood from most of the vessels that supply the walls of the heart with blood. § This blood in the right atrium is then squeezed into the right ventricle.

The Anatomy of the Heart •

The right ventricle pumps the blood into the next major vessel, the pulmonary trunk, which splits into the right pulmonary artery and the left pulmonary artery. § These arteries each carry the blood to a lung. § In the lungs, the blood releases the carbon dioxide it has been carrying and picks up oxygen. § The oxygenated blood returns to the heart via 4 pulmonary veins that empty into the left atrium. § The blood is then squeezed into the left ventricle.

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The left ventricle pumps the blood into the next great vessel, the ascending aorta. § From here the aortic blood goes to the coronary arteries (which supply the walls of the heart with oxygenated blood), the arch of the aorta (which sends arteries to the upper parts of the body), and the descending thoracic aorta, which becomes the abdominal aorta. § These arteries transport oxygenated blood to all parts of the body.

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The size of the chambers and the thickness of the chamber walls vary, due to the amount of blood received and the distance this blood must be pumped. § The right atrium, which collects blood coming from all parts of the body except the lungs, is slightly larger than the left atrium, which receives only the blood coming from the lungs. The thickness of the chamber walls also varies. § Ventricles have thick walls, whereas the atria are thin walled. § They are assisted with pumping blood by the reduced pressure caused by the expanding ventricles as they receive the blood. The thickness of the 2 ventricle walls varies also. § The left ventricle has walls thicker than the right ventricle since it must pump the oxygenated blood at high pressure through thousands of miles of blood vessels in the head, trunk, and extremities.

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The Valves of the Heart •

The valves of the heart are designed in such a way as to prevent blood from flowing back into the pumping chamber.

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There are 2 atrioventricular valves between the atria and their ventricles. § The valve between the right atrium and the right ventricle is called the tricuspid valve b/c it consists of 3 flaps or cusps. § These flaps are made of fibrous connective tissue that grows out of the walls of the heart and is covered with endocardium. § The pointed ends of the cusps project down into the ventricle. § Cord called chordae tendineae connect the pointed ends of the flaps or cusps to small conical projections called the papillary muscles located on the inner surface of the ventricle.

The Anatomy of the Heart §

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The atrioventricular valve between the left atrium and the left ventricle is known as the bicuspid or mitral valve. § It has 2 cusps or flaps, whose pointed ends project down into the ventricle with the same structures as the tricuspid valve. § It is the only valve in the heart with only 2 cusps; all others have 3 cusps.

The 2 arteries that leave the heart (the ascending aorta and the pulmonary trunk) also have valves that prevent blood from flowing back into the pumping chamber. § These are called the semilunar valves. § The pulmonary semilunar valve is found in the opening where the pulmonary trunk exits the right ventricle. § The aortic semilunar valve is found in the opening where the ascending aorta leaves the left ventricle. § Both of the valves are made of 3 semilunar cusps that allow blood to flow only in one direction....