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Anatomy and Physiology
Jacqueline Carnegie

Chapter 18 The Cardiovascular SystemHeart AnatomySize Location Orientation superior surface of diaphragm on topleft of the midline from 2nd rib to 5th intercostal between ribs spaceanterior in front to the vertebral column posterior to the sternum mediastinum middle of chest Coverings of the Heartthe heart is enclosed in a doublewalled sac called the pericardiumthe loosely fitting superficial part of this sac is the fibrous pericardiumprotects the heartanchors it to surrounding structuresprevents overfilling of the heart with blood below the fibrous pericardium is the serous pericardiuma thin slippery 2 layer serous membrane the parietal layer of the serous pericardium lines the internal surface of the fibrous pericardium it attaches to the large arteries exiting the heart and then turns and continues over the external heart surface of the visceral layer epicardium between the parietal and visceral layers is the pericardial cavity look at pg 663 which contains a film of serous fluid this allows the heart to work in a relatively frictionfree environment Layers of the Heart Wallthe heart wall consists of the epicardium myocardium and the endocardiumthe superficial epicardium is the visceral layer of the serous pericardium and is often infiltrated with fat especially in old people the myocardium is the middle layer and is composed mainly of cardiac muscle and forms the bulk of the heartit is the layer that contractsbranching cardiac muscle cells are tethered to one another by crisscrossing connective tissue fibres and arranged in a spiral or circular bundles the fibrous skeleton of the heart forms a dense network and reinforces the myocardium internally and anchors the cardiac muscle fibres it also limits the direct spread of action potentials across the heart to specific pathways the endocardium inside the heart is a glistening white sheet of endothelium squamous endothelium that rests on a thin connective tissue layerit lines the heart chambers and covers the fibrous skeleton of the valvesendocardium is continuous with the endothelial linings of the blood vessels leaving and entering the heart Chambers and Associated Great Valvesthe heart has 4 chambers2 superior atria and 2 inferior ventriclesthe internal partition that divides the heart longitudinally is called the interatrial septum where it separates the atria and the interventricular septum where it separates the ventricles the right ventricle forms most of the anterior surfacethe left ventricle dominates the inferoposterior aspect of the heart and forms the apextwo grooves visible on the heart surface indicate the boundaries of its 4 chambers and carry the blood vessels supplying the myocardium the coronary sulcus or atrioventricular groove encircles the junction of the atria and ventricles like a crown the anterior interventricular sulcus marks the anterior position of the septum separating the right and left ventricles and continues as the posterior interventricular sulcus Atria The Receiving Chambersexcept for protruding appendages called auricles little ear which increase atrial volume somewhat the right and left atria are remarkably free of distinguishing surface featuresthe right atrium has 2 basic partsa smoothwalled posterior part and an anterior portion where the walls are ridged by bundles of muscle tissue that look like the teeth of a comb and are called pectinate muscles pectincombthe posterior and anterior of the right atrium are separated by a Cshaped ridge called the crista terminalis terminal crest the left atrium is mostly smooth and pectinate muscles are found around the auricle functionally the atria are receiving chambers for blood returning to the heart from circulation small and thinwalled chambers since they contract minimally contribute little to the propulsive pumping activity of the heart blood enters the right atrium via 3 veins1 the superior vena cava returns blood from body regions superior to the diaphragm above the diaphragm2 the inferior vena cava returns blood from body areas below the diaphragm3 the coronary sinus collects blood draining from the myocardium 4 pulmonary veins enter the left atrium which transport blood from the lungs back to the heart
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