Hormones also contribute to regulation of the amount of blood that your heart pumps. Norepinephrine is one of several hormones that affect blood pressure by varying the quantity of blood your heart pumps. Because your heart is composed mostly of muscle that is affected by hormones, hormones can cause it to contract more vigorously with each beat. More vigorous contractions mean that more blood is pumped with each beat.Hormones also can change the total quantity of your blood. When the quantity increases, your heart pumps more blood and your blood pressure increases. Your kidney makes a hormone called renin, which increases blood volume because it causes your body to retain salt, which in turn causes retention of water. Some of this extra water joins your bloodstream and adds to the volume of blood in your body. Renin also causes formation of another hormone, angiotensin, which acts to constrict or squeeze the muscle cells of the arterioles.Your arterioles and heart are also regulated by your nervous system, specifically your autonomic nervous system, over which you have no conscious control. In the presence of any type of stress, including excitement or exercise, your body increases the quantity of blood that is pumped by your heart, and blood pressure goes up. Your autonomic nervous system also is responsible for releasing the hormone norepinephrine, which causes veins to contract and blood to return to your heart more rapidly. This also increases the amount of blood pumped by your heart.
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Monday, July 11th, 2011 | Author: admin
Category: Cardio & Blood- Сholesterol
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