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Vasoconstriction is the body’s way of narrowing the blood vessels. When the blood vessels are made smaller, less blood is able to go through them. This is important in stopping bleeding, keeping the body warm and keeping blood pressure normal. Vasoconstriction is also used to control blood flow to organsdepending on how much blood is needed there.

The body can cause vasoconstriction by flexing small muscles which are found around the walls of the blood vessels. Flexing or tightening of these muscles can be caused by natural signalsor using medications for many different reasons. =Natural Vasoconstriction= The human body uses signals that travel through the blood stream which tell the blood vessels to become smaller. Adrenalinein the body causes this effect. This natural response to stress is important because it restricts blood flow, by making blood vessels narrower, to areas of the body which are not needed in the fight or flight response. For example, in response to stress the amount of blood that goes to the intestines is lowered by vasoconstriction. This way the blood can be diverted to muscles, like the heart.

Reducing Blood Loss
Blood loss is a serious medical emergencythat happens in patients who are bleeding on the inside or on the outside of their body. In order to keep the body and organs working, they need a certain amount of blood to stay alive. Vasoconstriction keeps the blood pressure near normal by making the blood vessels smaller, which causes the blood to fill up more of the vessels. Making blood vessels smaller in bleeding parts of the body also lowers the amount of blood that is lost from that area. This keeps the heart pumping the required amount of blood. If enough blood is lost, the body cannot make the blood vessels any smaller and the person can die.

Controlling Body Temperature
Vasoconstriction can be used to control a person’s body temperature. When a person is cold the body makes the blood vessels smaller in order to move blood from where it is not needed to where it is needed. This is most often seen on the skin of people who are cold. Areas which have a lot of blood vessels in the skin often turn a pale color when cold because blood flow to the skin is decreased. By decreasing the amount of blood to a cold part of the body the blood stays warmer. This warmer blood then keeps the rest of the body warm. =Medicine and Vasoconstriction= A wide range of medications and illegal drugscan act as vasoconstrictors. These drugs act like the natural adrenaline in the body, by signaling to the blood vessels they should become smaller. Vasoconstrictors make up groups of medications which can treat symptoms from low blood pressure to nasal congestion. All of these symptoms can be treated by making blood vessels smaller and decreasing blood flow, either throughout the body or in a smaller area (e.g. the nose and sinuses). Vasoconstrictors can also be used during surgery to both reduce blood flow to areas being operated on and can keep other medicines, like anesthetics, in areas of the body doctors would like to keep them in. Also, people with brain injuries that cause swellingof the brain are often given vasoconstrictors. Reducing the amount of blood in the injured brain can prevent too much swelling. This increase in swelling can cause too much pressure on the brain, which can lead to death. Limiting the amount of fluid in the brain reduces this dangerous pressure.

The following are examples of medicines or groups of medicines that cause vasoconstriction: =Unwanted Vasoconstriction= Not all vasoconstriction is good. Vasoconstriction, for any reason, of the blood vessels which supply blood to the heart can cause chest pain known as angina. This chest pain is often associated with heart disease and can be reversed by vasodilating the blood vessels, or making them larger. The reduction in blood flow causes the heart to work harder than it has fuel for and this decrease in blood and oxygen causes pain which is similar to that in muscles after periods of exercise. Additionally, vasoconstriction for long periods of time, and reduced blood flow can cause permanent damage. Instead of protecting the body by keeping blood from leaving the blood vessels, vasoconstriction can starve organs or muscles of much needed blood and cause permanent injury or illness.
 * Amphetamines
 * Antihistamines
 * Caffine
 * Cocaine
 * LSD
 * Phenylephrine
 * Psuedoephedrine
 * Psilocybin