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The Heart. The Heart. right pulmonary arteries semilunar valves right atrium superior vena cava right pulmonary veins Inferior vena cava septum aorta left pulmonary arteries pulmonary trunk left ventricle left pulmonary veins right ventricle left atrium atrioventricular valve.
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The Heart • right pulmonary arteries • semilunar valves • right atrium • superior vena cava • right pulmonary veins • Inferior vena cava • septum • aorta • left pulmonary arteries • pulmonary trunk • left ventricle • left pulmonary veins • right ventricle • left atrium • atrioventricular valve
Control of the Heartbeat • You cannot hold your pulse even for a single beat. • Your heart continues beating regularly if you are knocked unconscious, and may even continue beating for a while after you die. • The impulse that triggers the heartbeat actually originates from within the heart itself. • There are nerves (autonomic NS) that connect to the heart but they do not initiate or control the heartbeat • A cardiac cycle is defined as a complete cardiac movement, including systole, intervening pause, and diastole
Control of the Heartbeat • The contraction phase is systole, while the filling phase is diastole • A bundle of specialized muscle tissue, located in the wall of the right atrium, stimulates the muscle fibres to contract and relax rhythmically. • Thesinoatrial node (S-A node) = the pacemaker • Atria contract while ventricles relax, and the ventricles contract while atria relax. • Heart sounds are created primarily from turbulence in blood flow created by valves closing, not from contraction. • Why do heart sounds come in pairs?
Control of Heartbeat • The Atrioventricular (AV) node is also located on the right side of the heart, just beneath the surface of the interventricular septum. • The Bundle of His, is a band of nerve fibers that originates at the AV node, then passes along the interventricular septum to the ventricles. • The right and left bundle branches proceed along the right and left sides of the interventricular septum to the tips of the two ventricles. • The Purkinje Fibers are the tree-like terminal branchings of the right and left bundles.
Control of Heartbeat • After the SA node fires: • the electric signal spreads throughout the muscles of both atria • Atrium contract • The impulse then passes through the AV node to the Bundle of His • The signal is then divided between right and left bundle branches • When they reach the terminals of the Purkinje fibers they leap across to the cardiac muscle fibers • Ventricles contract • All this happens in less than a second.
Electrocardiographs (ECGs) • Represents (and measures) the electric activity of the heart • A normal ECG graph appears as follows:
An upward deflection of the wave represents an electric impulse traveling towards a sensor
ECGs • Each of the letters designates a different phase of the cardiac cycle. • P wave: generation of the electrical impulse at the SA node and its subsequent spread through the atria. • PR interval: During this interval the impulse travels through the atria and the AV node.
ECGs • QRS complex. The time necessary for the impulse to spread through the bundle of His and its branches to complete ventricular contraction • ST segment. The ST segment represents the period between the completion reversal of charges in the ventricular muscle tissue. • T wave. The T wave represents the return to normal state of ventricular muscle tissue that occurs after ventricular contraction.
Chemical Regulators • When you are relaxed, your S-A node fires regularly • around 70 times a minute. • This firing rate adjusts, however, to meet your body’s needs. • Read the Chemical Regulators section on p. 305 • There are two negative feedback loops described • Fill in the worksheet with the appropriate information for each of these loops
Control of Heartbeat • Physical activity is not the only trigger for an increased heart rate. • The nervous system releases adrenaline when you are nervous, angry, or excited, or after a sudden shock or sharp pain. • “fight or flight” response: • a physiological change that prepares the body for anticipated activity • attack, defence, or escape. • As the heart rate increases, so does blood flow to the muscles, resulting in more oxygen being delivered to the muscle cells.
Cardiac Output • The amount of blood pumped by the heart is often referred to as the cardiac output • = volume of blood pumped from each ventricle per unit of time. • a measure of the level of oxygen delivery to the body • Indicatesthe total level of work the muscles must perform • Two factors affect the cardiac output • heart rate (HR) = number of times the heart beats in a unit of time (minute) • stroke volume (SV) = the amount of blood forced out of the heart with each heartbeat cardiac output = SV × HR • Average person has a stroke volume of about 70 mL and a resting heart rate of about 70 beats per minute, for a cardiac output of about 4900 mL/min.
Cardiac Output • Out of Shape • Average • Extremely Fit
Cardiac Output • Individual A = Average • Individual B = Out of Shape, Unhealthy • Low stroke volume results in a high resting heart rate • Individual C =Exceptionally fit • very high stroke volume results in a low resting heart rate • can maintain the same level of oxygen delivery at a much lower heart rate than the less fit individual B. • Why is a low resting heart rate healthier? • When the heart is forced to work harder, it will break down sooner
ECGs Activity: • Research 1 of 3 other conditions on www.ecglibrary.com • left ventricular stenosis • atrioventricular block • Wolf-Parkinson White • Draw a normal ECG • Draw the abnormal ECG for the condition • Identify where the major differences are (which sections of the ECG) between the two ECGs • Explain the pattern and cause of the abnormal ECG
