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Unformatted text preview: Ch 18: The Cardiovascular System: The Heart The heart is at the center, structurally and functionally, of the cardiovascular system. It is the heart that provides the power to move blood through blood vessels and it is at the heart that the 2 separate circuits within the circulatory system the pulmonary and the systemic meet. If the heart does not function properly all bodily systems will be affected, since blood will not flow normally through its circuits and tissues will be deprived of gas exchange, nutrient delivery and waste removal. The ability of blood to reach tissues and perform these functions is called perfusion . If blood cannot perfuse tissue, that tissue will suffer ischemia , which can lead to tissue death. OVERVIEW + terminology The heart sits in the center of the thoracic cavity, between the pleural cavities containing the lungs, in anterior to the vertebral column and behind the sternum and ribcage (bony thorax) = the mediastinum. The heart is slightly tilted to the left: Inferior point= apex Superior surface= base The heart itself is contained w/in the pericardial cavity formed by the pericardial sac : Outer layer of sac = pericardium ( peri = around, cardium=heart )=dense collagenous network of fibers Inner layer of sac = outer layer of heart = epicardium ( epi =over, cardium=heart)= dense fibrous connective tissue, areolar tissue, simple squamous epithelium Beneath the epicardium is the muscular layer of the heart---> myocardium The chambers of the heart are lined w/simple squamous epithelium= endocardium Blood vessels are named based on whether they are carrying blood to the heart ( veins ) or away from the heart ( arteries ). W/in the systemic and pulmonary circuits, arteries are connected to veins by capillaries . The pulmonary circuit operates between the heart and the gas exchanges surfaces of the lungs. The systemic circuit operates between the heart and all the organs and tissues of the body. ANATOMY of the Heart The heart is divided into 4 chambers, 2 top and 2 bottom Each upper chamber is an atrium----> R & L atria (the flap-like edge of each atrium=an auricle) Each lower chamber is a ventricle-----> R & L ventricles The atria are thin-walled, the ventricles are thick walled, which reflects their functions (see below). The chambers are separated by septa: an atrioventricular septum divides top from bottom An interventricular septum divides right from left On each side of the heart, the upper & lower chambers are connected through valves, which can be open (allowing blood flow btwn chambers) or closed (preventing blood flow btwn chambers). R side = R atrioventricular valve, or the tricuspid valve L side = L atrioventricular valve, or the biscuspid , or mitral valve These valves are anchored by strands of dense fibrous connective tissue (chordae tendinae ) to pads of muscle on the ventricular walls called papillary muscles....
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