THE MYOCARDIUM (HEART MUSCLE): THE STRUCTURE & THE CELLS OF HEART MUSCLE
Structure of the Myocardium (Heart Muscle)
The heart is shaped like a co the point (apex) at the bottom broader base at the top. The apex of the heart is the tip of the ventricles and points down to the left sic chest. The wide upper part of the heart includes the right and left atria origins of the major blood vessels.
The heart has three layers o the myocardium, the epicardium, and the endocardium. The myocardium is the thick main layer of heart muscles. Its outside surface is covered b) glossy membrane called the epicardium. Another smooth, gloss membrane, the endocardium, covers the inside surfaces of the four heart chambers, the valves, and the muscle that attach to the valves.
Myocytes: The Cells of the Heart Muscle
The myocardium is composed of individual muscle cells called myocytes. These myocytes act together to contract and relax the heart chambers in the correct sequence to pump blood to the lungs and the body.
Although the cells are individual units, they are coordinated and work together. Remember, the purpose of the heart is to pump blood. It is able to accomplish this pumping in a coordinated manner because of the way the cells are arranged and because electrical messages can pass easily between the cells.
When filaments within the heart muscle cells contract, the cells shorten. Shortening of the cells contracts the heart muscle and so makes the pumping chambers become smaller; as a result, blood is squeezed out. When the filaments within the cells relax, the cells lengthen and the heart muscle relaxes; the relaxation makes the pumping chambers expand. When the chambers expand, blood flows back into them.
Cardio & Blood-holesterol
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