Vasoconstrictor: controls the volume of the circulation

2021-05-27 02:30 PM

When the sympathetic nervous system is stimulated, the sympathetic nerve endings in specific tissues release norepinephrine, which stimulates the heart and constricts the veins and arterioles.

Fluid control of circulation means controlling secretions or absorption into body fluids such as hormones and factors that are produced. One of the substances produced by special glands and transported in the blood throughout the body. The rest are generated from local tissues and cause only local circulatory effects. The most important humoral factors affecting circulatory function are described in the following sections.

Norepinephrine vĂ  epinephrine

Norepinephrine is a potent vasoconstrictor hormone, epinephrine is less abundant and in some tissues even mild vasodilation (a particular example of epinephrine-induced vasodilatation is the occurrence of coronary vasodilation during increased cardiac activity). .

When the sympathetic nervous system is stimulated in most parts of the body during stress or exercise, the sympathetic nerve endings in individual tissues release norepinephrine, stimulating the heart and contracting the heart. veins and arterioles. Furthermore, the sympathetic nervous system in the adrenal medulla tells its glands to secrete both norepinephrine and epinephrine into the bloodstream. These hormones circulate to all areas of the body, causing most of the circulatory effects such as sympathetic stimulation: (1) sympathetic nerve stimulation (2) indirect effects of norepinephrine and/ or the effect of epinephrine on the circulation.

Angiotensin 2

Angiotensin 2 is another vasoconstrictor. Less than one part per million per gram can increase a person's arterial pressure by 50 mmHg or more. The effect of Angiotensin 2 is strong vasoconstriction on small arteries. If vasoconstriction occurs in isolated areas of tissue, blood flow to the area may be disrupted. However, the real importance of angiotensin 2 is that it acts normally on the arterioles of the body at the same time to increase the resistance of the entire peripheral vessels and to decrease the renal excretion of fluids and electrolytes. , thereby increasing arterial pressure. Therefore, this hormone plays a sensitive role in the regulation of blood pressure.

Vasopressin

Vasopressin also called the antidiuretic hormone, is even more potent than angiotensin 2 so it is one of the most powerful vasoconstrictors in the body. It is produced in neurons in the hypothalamus system of the brain but is then transported down to the posterior pituitary by axons, where it is secreted into the bloodstream. Vasopressin has a powerful effect on the function of the circulatory system. Because only small amounts of vasopressin are secreted under most physiological conditions, most physiologists think that vasopressin plays a minor role in vascular control. However, experiments have shown that the circulating concentration of vasopressin after severe bleeding can be increased to increase vascular pressure to 60 mmHg. In many examples, the possible effect is to return arterial pressure to near normal. Vasopressin has a major role in increasing the reabsorption of water from the renal tubules into the bloodstream and thus helping to control the body's fluid volume. That is why this hormone is called the antidiuretic hormone.