Discuss the events of one cardiac cycle (electrical and mechenical events) - Essay Example

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The cardiac cycle refers to the flow of blood or blood pressure that begins with one heart beat to the next, and is coordinated by a sequence of impulses that are either mechanical or electrical. From a mechanical perspective, the cardiac cycle is due to movement of blood. The…
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Discuss the events of one cardiac cycle (electrical and mechenical events)
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The Cardiac Cycle The cardiac cycle refers to the flow of blood or blood pressure that begins with one heart beat to the next, and is coordinated by a sequence of impulses that are either mechanical or electrical. From a mechanical perspective, the cardiac cycle is due to movement of blood. The frequency of the contraction and relaxation of the cardiac muscles is referred to as the heart beat. The cardiac is a special muscle that contracts continually without taking a break, and the importance of the cycle is to maintain blood flow to an individual and supply blood pressure to ensure adequate circulation. Cardiac muscles are myogenic, which means that their contractions are started by the muscle itself, the action beginning from the sino-atriol node. The first stage of the cardiac cycle is known as the ventricular filling, which involves the flow of blood from the atria to the ventricles. The other stages include the movement of blood from the right ventricle through the pulmonary artery and the left ventricle through the aorta (Guyton and Hall, 2006).
The contraction of the heart muscles on the left and right atria, which contract at the same time, is known as the atria systole (Klabunde, 2012). The events begin with the electrical current, which stimulates the myocardium contracts the heart chambers. This is then followed by the mechanical events. The electrical currents of the heart begin at the Sino atria node where action potential is generated (Williams, 2001). In the Sino-atria node, there is a rich supply of cells, capillaries and nervous supply, and the electrical current travels across the right and left atria. The atria are separated from the ventricles by a non-conducting band of connective tissues. Between the cardiac muscles are disc called gap junctions that provide electrical resistance at a low rate. The stimulation of each muscle fiber causes an electrical current to pass over the whole heart hence no external stimulus is required.
The wave reaches the atrio-ventricular nodes in the lower right atrium, where it delays for a short period of time before conduction to the ventricles through the bundles up the purkinje fibers (Klabunde, 2004). Delaying at the atrio-ventricular node allows enough time for blood in the atria to get into the right ventricles. The atrio-ventricular node may act as a pace maker, which makes the action potential slow and unstable, depolarization occurs constantly due to the fall of calcium and potassium ions and this effect on the resting potential affects the heart rate.
The mechanical sequences of the cardiac cycle are brought on by the rhythmic changes in the cardiac muscles, which include the relaxation and contraction of the muscle (Waxman, 2006). The mechanical events of the cardiac cycle in the left side of the heart include changes in pressure in the aorta and in the left ventricle, heart sounds and change in blood volume. Contractions begin when the ventricles are excited and cause an increase in the pressure in the ventricles, after which the atria ventricular valves close causing a heart sound. The chambers of the ventricles then become closed, after which there is iso-volumetric contraction where the pressure increases rapidly becoming more than the pressure in the pulmonary artery and aorta, hence opening the semi lunar valve.
Guyton, A.C. and Hall, J. E. 2006. Textbook of Medical Physiology. Philadelphia: Elsevier.
Klabunde, R. 2004. Cardiovascular Physiology Concepts. Boston: Lippincott Williams & Wilkins.
Klabunde, R. 2012. Cardiac Cycle. [Online]. Available
Waxman, S. 2009. Clinical Neuroanatomy. Boston: McGraw-Hill Medical.
Williams, G. 2001. Advanced Biology for You. New York: Nelson Thornes. Read More
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