1. Describe the cellular and sub-cellular process of excitation- contraction coupling, and the role of calcium in cardiac muscle cell.
2. Write and essay on short term and long term regulation of blood pressure. Add a note on the renin-angiotensin system used as a drug Targeting system to control high blood pressure. For calcium in cardiac muscle cell..
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Cellular and Sub-Cellular Processes of Excitation
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Cellular and Sub-Cellular Processes of Excitation
All the people owe much to the feeling in their lives owing to the beating of their hearts. Schlüter (2016) points out that the heartbeats are products of cellular mechanisms of excitation-contraction (EC) coupling. The excitation-contraction coupling has since become a critical component of the pathology and cardiac physiology. Consequently, it has led to a greater interest in the understanding of the sub-cellular, cellular, and even the molecular pathways of the cellular excitation process.
The Excitation-Contraction (EC) Coupling
The concept of the excitation-contraction (EC) coupling has been defined as the processes at the cellular level that precedes electrical excitation leading to the activation of the myofilaments (Schlüter, 2016). The excitation-contraction (EC) coupling has been found to control the cardiac and skeletal muscles, with some notable differences. Plopper et al. (2015) point out that the resting muscles cells have a much-reduced concentration of Ca2+ in the cytol in comparison to the concentration outside the cell and inside the SR Ca2+ storage organelles. When the excitation-contraction (EC) coupling commences, the Ca2+ enters the cytosol and exits it as the cell starts to enter the resting position. The process creates an increase and reduction of cytosolic Ca2+ concentration that goes on in the cells. The process of the repeated increase and decrease in the Ca2+ cytosolic concentration is termed as the Ca2+ transient.
The process of excitation-contraction (EC) coupling in a cardiac cell is divided into four major steps. According to Plopper et al. (2015), the first step is the initiation of a signal at the sarcolemma through the process of polarization. During this process, a potential is created when the membrane becomes more positive relative to its resting potential due to an incoming action potential. The Cav channels that are voltage-dependent sense the change in membrane potential thus opening during the second phase of the cardiac action potential. The result is a flow of the calcium ions (Ca2+)through the established electrochemical potential and down into the cell. The second phase is the calcium ions (Ca2+) influx through the Cav 1.2 Ca2+ channels that are responsible for the stimulation of the release of Ca2+ from the SR Ca2+ organelle (Plopper et al., 2015). The SR Ca2+ organelle has been found to have storage of calcium ions in millimolar concentration. Schlüter, 2016,) points out that the excitation and contraction of the cardiomyocytes are linked with the change in the concentration of the Ca2+. The process begins with the triggering of the Ca2+ release from the sarcoplasmic reticulum. This leads to the sarcolemmal Ca2+ influx leading to an increase in the intracellular Ca2+………………………………………………………………………………………………
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