BSC 1086C Chapter 18: Chapter 18 book notes

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Florida Gulf Coast University
Biological Sciences
BSC 1086C

Chapter 18- Cardiac Physiology Cardiac muscle contraction - The sinoatrial node or SA node is the physiological pacemaker of the heart. o It depolarizes faster than any other part of the autorhythmic system. o 90-95 action potential (= heart beats) per minute - The atrioventricular or AV node depolarizes slower than the SA node (40-60 potentials per minute) - The atrioventricular bundle or bundle of His is the only electrical connection between atria and ventricles. - It splits into right ad left bundle branches that run inside the interventricular septum toward the apex of the heart. - Purkinje fibers spread all over the myocardium of both ventricles (30-40 bpm) - Defects in the cardiac conduction system may be cause of an irregular heartbeat (arrhythmia) and even lead to fibrillations o Abnormal pacemaker called ectopic focus takes over. ▪ AV nodes take over and develop 40-60 bpm. o Partial or total heart block may develop and few or no impulses from the SA node reach the ventricles. - There are two cardiac center located in the medulla oblongata. o Cardioacceleratory centers sends signals via sympathetic fibers to SA and AV node, cardiac muscle cells, and coronary arteries. ▪ Increase heart rate, increase contractility, and increase the blood flow to the heart. o Cardioinhibitory center only inhibits SA and AV nodes through parasympathetic fibers in the vagus nerve Electrocardiography - Electrocardiogram (ECG, EKG) can measure the flow of ions across the sarcolemma during repolarization and depolarization and displaying in form of static and dynamic recordings. o P Wave is caused by depolarization of SA node o QRS complex is caused by ventricular depolarization o T wave is caused by ventricular repolarization Heart Sound - AV valves up and the valves close o First audible sound of the cardiac cycle is called the first heart sound - Course of the semilunar valves o Second heart sound occurs later in the heart cycle. - Both heart sounds are not closing sounds of the valves, but are caused by turbulent blood flow. - Abnormal sounds are called heart murmurs. o Cause: malfunction of a heart valve o If a valve doesn’t close completely the condition is called the insufficiency or regurgitation - Eight basic valve defects with impairment of blood flow. o Tricuspid stenosis: obstructs the flow from right atrium and right ventricle o Tricuspid regurgitation: blood flows back from right ventricle to right atrium. o Pulmonary stenosis: obstructs flow into the pulmonary trunk o Pulmonary regurgitation: blood flows back into the right ventricle o Mitral stenosis: obstructs the flow from the left atrium and left ventricle o Mitral regurgitation: blood flow back from the left ventricle and left atriums o Aortic stenosis: blood flow back into the aorta o Aortic regur
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