Anatomy And Physiology Test 2 Answers

805 Words 4 Pages
Jennifer Datus
Anatomy and Physiology II
Essay Questions Test 2
Professor Vernet

1. The beginning of the cardiac cycle starts with deoxygenated blood from the systemic circulation entering the heart into the right atrium from the superior and inferior vena cava. A chamber of the heart beats because of the electrical impulses located around areas of the heart that travel across the heart which allows the muscles to contract.The SA node located in the right atrium is also known as the pacemaker of the heart, this node conducts an electrical impulse that makes the right atrium contract causing the tricuspid valve to open and for blood to pass through into the right ventricle. Then when the right ventricle is ready to contract the tricuspid
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But before this, the impulse travels along the Bundle of His which separates into two branches, the right and left bundle branches which lie in the septum.The branches spread into Purkinje fibers that lie in inner walls of the ventricles. The reoxygenated blood then comes back from the lungs through the pulmonary veins and fills the left atrium. The left atrium then contracts opening the mitral valve and allowing blood to fill up the left ventricle. The left ventricle contracts closing the mitral valve and opening the aortic valve. The aortic valve opens, and blood is pushed through the valve into the aorta and distributed throughout the body.After ventricular contraction in order to prevent blood from regurgitating back from the aorta into the left ventricle the aortic valve closes. The heart makes a sound throughout its cycle known as “lub dub”. The first heart sound lub is due to the atrioventricular tricuspid and mitral valve closing and the second sound dub is the closing of the semilunar valves, aortic and pulmonary. During diastolic also the point at which the heart is relaxed, the AV valves are opening …show more content…
Cardiac muscle cells are short, striated, branched, and interconnected. This cells usually have one nucleus but there are times when you can see two nuclei. Cardiac muscle cell contain large mitochondria that allows the heart to to not get tired. Z discs, A bands and I bands are all found in it’s sarcomere. These cells also contain a small amount of T tubules. Cardiac muscle cells and skeletal muscle cells both depolarizing action potentials causes muscle contraction. Depolarization waves travel down the T tubules causing the SR to release calcium. Calcium then binds to troponin causing sliding filaments. The difference between these cells is that cardiac cells beat alone they don’t need nervous system circulation. All cardiomyocytes contract as one unit whereas skeletal contracts independently. Cardiac cells also contain longer refractory period than skeletal therefore tetanic contractions don’t occur. Cardiac cells cannot function without oxygen, they require aerobic respiration meanwhile if skeletal muscles don’t have oxygen they can go through

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