Heart blood supply 4 points the first branches off

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Heart Blood Supply: (4 points)
BIO 202 – Chapter 18
Page 4
What is a myocardial infarction? (1 point) A heart attackCardiac cycle: (13 points)The cardiac cycle consists of (1) the atria beating in unison (atrial systole), (2) the contraction of both ventricles, (ventricular systole), and (3) the entire heart relaxes for a brief moment (diastole).During the cardiac cycle, pressure within the heart chambers rises and falls with the systole and diastoleof atria and ventricles.When the atria fill, pressure in the atria is higher than that of the ventricles, which forces the atrioventricular valves open. Pressure inside atria rises further as they contract, forcing the remaining blood into the ventricles.When ventricles contract, pressure inside them rises sharply, causing atrioventricular valves to close andthe pulmonary and aortic valves to open.As the ventricles contract, papillary muscles contract, pulling on chordae tendineae and preventing the backflow of blood through the A-V valves.Heart sounds: (4 points)Heart sounds are described as a "lubb-dupp" sound.The first sound (lubb) occurs as ventricles contract and atrioventricular valves are closing.The second sound (dupp) occurs as ventricles relax and aortic and pulmonary valves are closing.Cardiac Conduction system (4 points)Specialized cardiac muscle tissue conducts impulses throughout the myocardium and comprises the cardiac conduction system.A self-exciting mass of specialized cardiac muscle called the sinoatrial node (or pacemaker) is located onthe posterior right atrium and generates the impulses for heart contraction. This node initiates impulses
BIO 202 – Chapter 18
Page 5that spread throughout the myocardium and is self-exciting (-it does not require a signal from the nervous system).Impulses from the S-A node quickly spread throughout the atria and cause them to contract. Impulses also spread to the atrioventricular (A-V) node. The A-V node rapidly sends a signal down the AV bundle and into the interventricular septum. These impulses rapidly spread through purkinje fibers into the walls of the ventricles and cause the ventricles to contract.

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