The Heart Coverings of the Heart Heart Wall Pericardium friction reducing fluid filled space between which is the pericardial cavity The sack like enclosure of the heart it has visceral and parietal layers and a Epicardium the outermost covering it is the same thing as the visceral pericardium the cardiac muscle a thin epithelial lining of the heart chambers Myocardium Endocardium Valves structures that prevent backflow meaning they allow flow in only one direction 2 types 1 Atrioventricular The bicuspid on the left and the tricuspid on the right Each consists of two or three cusps triangular flaps valves are each located between an atrium and a ventricle The pointed end of the triangle points into a ventricle In the same direction as the blood flow When the heart ventricle contracts pumps blood pressure closes the valve and blood cannot go back into the atrium prevents backflow attached to each cusps are cords the chordae tendineae which run to the papillary muscles these cords prevent the cusps from everting going all the way through the opening weak or stretched chordae tendineae can lead to prolapse and leaky valves 2 Semilunar Valves located between a ventricle and its exiting artery They work slightly different when a ventricle contracts the pressure opens a semilunar valve and blood goes through When the ventricle relaxes the exiting blood tries to backflow but this closes the valve The Cardiac Cycle The 2 atria contract pumping blood into the two relaxed ventricles then The ventricles contract while the now relaxed atria are refilled by either the vena cavae or pulmonary veins Systole Diastole the phase of contraction the phase of relaxation During ventricular diastole the tri and bicuspids are open the semilunar close the two atria are in systole and the ventricles are filling During atrial diastole ventricular systole the cuspids close the semilunars open and the ventricles empty while the atria fill up Then there is a brief pause and it repeats 72 beats min Conduction system The cardiac muscle contracts without neural stimulation It has intercalated disks which weave the cell ends together this allows easy communication between cells thus the cells beat as a unit The orderly sequence of atrial then ventricle systole is maintained by an intrinsic and or the autonomic nervous system can vary the cycles rate The conduction system consists of specialized muscle tissue which can generate and These impulses stimulate cardiac muscle to contract in cycles as a unit internal regulatory system Hormones not start or stop it conduct electrical impulses These tissues include Sinoatrial node SA node or pacemaker located in right atrial wall initiates cardiac cycle sets pace by sending impulses to both atria causing them to contract The impulse also travels to the atrioventricular node AV node located between the rt Atria and rt Vent which sends impulses to both ventricles over a bundle of branching fibers the frequency of the S A node s impulses can be neutrally and or hormonally varied Other Heart Terms the atria each have expandable appendages called auricles in the wall separating the two atria interatrial septum is a depression scar called the fossa ovalis it used to be an opening during fetal development such that blood could flow from the right atrium to the left atrium the wall between the two ventricles is called the interventricular septum the heart has its own circulatory system Coronary circulatory system most heart problems can be traced to faulty coronary circulation coronary artery disease Ischemia Angina Infarction Myocardial infarction usually due to ischemia infarction and a weakened heart of vessels decreases of blocks flow above reductions in blood supply reduced blood flow weakens heart muscles cells chest heart pain due usually to ischemia buildup of cholesterol and or other fatty compounds on the inside a condition of damaged heart muscle due to one of the death of tissue due to an interrupted blood supply Coronary artery disease Atherosclerosis heart attack Heart murmur unusual sounds generally due to valve disorders leaky valves faulty chordae tendineae valve cusps damaged by disease rheumatic fever and endocarditis stenosis refers to cusps which are stiff due to the buildup of scar tissue
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