Cardiovascular System

Cardiovascular System - Cardiovascular System I....

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Cardiovascular System I. Introduction: Skeletal and Cardiac muscle a. Similarities i. Function to contract and re-lengthen ii. Functional cell type is a myocyte iii. Contraction requires excitation-contraction coupling iv. Critical proteins needed for regulation of contraction found only in myocytes themselves. b. Differences i. Heart does not require neural stimulation to contract. ii. Most heart cells spontaneously depolarize (~1/sec) and those in the SA node do it the fastest = Pacemaker cells iii. Heart contracts upon itself, a force that applies pressure to the blood in the ventricles. iv. Rate and strength of contraction depends on autonomic tone. v. The ability to pump blood is tied to the physiology of the vasculature. vi. ACh (muscarinic) and adrenergic (beta-1) stimulation regulate both mechanical and electrical properties of the heart. (no nicotinic receptors on the heart) II. The Cardiac Cycle a. Used blood returns through vena cava and enters right atrium . Increase in pressure forces the tricuspid valves open and allow blood to go into right ventricle b. When both atrium and ventricle are full of blood atrium suddenly contracts and pushes all the blood into the ventricle which contracts more powerfully into the pulmonary artery . c. Tricuspid valves prevent blood from being pushed back into the atrium. Tendinous cords prevent the valves from being turned inside out. Semi lunar valves prevent blood falling back into the ventricle. d. Pulmonary artery takes the blood to exchange carbon dioxide with oxygen. The oxygenated blood returns to the left ventricle via the pulmonary vein and gets pumped to the rest of the body. e. Flow of blood is the same on the right side but bicuspid valves instead of tricuspid. Blood enters the aorta and flows to the rest of the body. III. Systole and Diastole a. Cardiac muscle fibers relax and contract within a single functional organ as opposed to skeletal muscle where application of force moves the muscle. b. Systole -all cells in organ contract at every beat (synctium) i. Right side contracts first then left side ii. As deoxygenated blood is being pumped from the right ventricle to the lungs, oxygenated blood is being pumped from the left ventricle to the aorta. c. Diastole - timed relaxation after systole and heart fills with blood
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d. Complete cycle is controlled by electrical impulses in the heart wall. IV. Afterload and Preload a. Afterload - load against which the heart must contract is a volume of blood that is at the same pressure in the aorta when the aortic valve opens. i. Increase in afterload = decrease in cardiac output b. Preload - volume of blood comes into the heart at a different pressure (aortic valve closed and mitral valve open) also called filling pressure i. Filling and stretching of the heart affects its subsequent contraction. ii.
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Cardiovascular System - Cardiovascular System I....

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