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(7) Heart Attack and Cardiac Disorders

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Heart Disease and Heart Attacks

heart

What is the nerve control of the heart?

Two separate nervous systems link your heart and your brain. The sympathetic (accelerator) system releases noradrenalin and speeds up your heart rate, whereas the vagus (inhibitory) system tends to slow your heart rate. The major effect of the vagus system is to depress the frequency of heart impulses fired by the sinus node.

You could compare this function with that of an automobile: the sympathetic nerve works like the accelerator, and the vagus nerve acts like the brake. Thus, your nervous system controls your heart functions according to the needs of your body.

Maintaining the normal contractile (pumping) force of your heart depends primarily upon the influence of the sympathetic nerve. This nerve increases the pumping action of the heart muscle and thus increases your heart rate.

What are the coronary arteries of a normal heart?

Your heart has two major (coronary) arteries: the right coronary artery and the left main coronary artery with many small branches. These coronary arteries, like other arteries that supply blood to other parts of your body, branch off from the aorta. Your heart has to receive oxygen and necessary nutrients constantly from these coronary arteries rather than from the blood passing through the heart chambers.

The coronary artery is relatively small, with a diameter of about 2 to 3 mm in a normal heart. In such a normal heart, the diameter (caliber) of the coronary arteries enlarges to supply larger amounts of blood to the heart muscle when the heart needs to increase its pumping action.

When the size of the coronary arteries is narrowed, usually as a result of atherosclerosis (hardening of the arteries), only an inadequate supply of blood to the heart muscle is possible. The narrowing (stenosis) of the coronary artery is called coronary artery stenosis, and it may not produce obvious symptoms in its early stage.

When the narrowing of the coronary artery progresses further, an affected patient begins to experience chest pain, especially during physical exertion. This entity is called angina pectoris, or angina, often signaling the beginning of a heart attack.

When the atherosclerosis becomes far-advanced, it may completely block one or more coronary arteries, which causes a portion of the heart muscle to receive no blood supply at all. This stage of coronary artery disease is called myocardial infarction (MI). “Myo” means muscle, “cardial” means heart, and “infarction” means dead tissue: thus, dead heart muscle. Heart attack in lay peoples’ terms means myocardial infarction in medical terms.

Your nervous system controls your heart functions according to the needs of your body.

When the atherosclerosis becomes far advanced, it may completely block one or more coronary arteries.

Terms:

Sympathetic system - nerve system that speeds up the heart rate.

Vagus system - inhibitory nerve system that slows the heart rate.

Coronary artery - blood vessel in the heart that supplies nutrients and oxygen-rich blood to the heart muscles.

Atherosclerosis - hardening of the arteries, the usual cause of angina pectoris and heart attack.

Stenosis - narrowing.

Coronary artery disease - heart disease due to narrowing or blockage of coronary arteries from atherosclerosis.

Myocardial infarction - heart attack.

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