Vasodilatation, also referred to as vasodilation, is the widening of blood vessels that occurs when the muscles in the walls of such vessels become relaxed. Vasodilatation can occur for many different reasons, from drugs to exercise. It is the opposite of vasoconstriction, by which the blood vessels constrict and narrow. The dilation of blood vessels leads to a decrease in blood pressure, while the constriction of blood vessels leads to an increase. Either process can be restricted to a single organ or organ system, or it can happen throughout the entire body.
Anything that leads to vasodilatation is known as a vasodilator. Vasodilators can be natural or artificial and they can be internal or external. Some medicines are vasodilators; these are usually used to control high blood pressure. Dilation and constriction of blood vessels occurs almost nonstop based on the amount of blood that is needed in any given part of the body at any given moment. It can also occur because of various hormones or signals in the nervous system.
Drugs that induce this condition are commonly used to treat several different conditions. They are frequently used to treat hypertension, a condition in which one persistently has very high blood pressure. They can also be used to treat heart conditions such as angina and congestive heart failure by maintaining a lower, healthier blood pressure. Maintaining a lower blood pressure through the use of medications that lead to vasodilatation can reduce the risk of many different heart-related illnesses in those with abnormally high blood pressure.
In some warm-blooded animals, this process is one method by which a consistent, healthy temperature is maintained. When the external environment is very warm, some of the blood vessels of such animals will dilate and redirect warm blood to the skin or extremities of the animals. When the warm blood is close to the skin, heat can escape into the environment, cooling the animal down to better temperatures. When the outside environment is cold, vasoconstriction can occur and have the opposite effect, keeping the warm blood around the animal's vital organs.
There are many different things inside and outside of the human body that can cause vasodilatation. Inside, histamine and lactic acid are among the many different chemicals that can cause blood vessels to dilate. Exercise and muscle work can also cause the dilation of some blood vessels. External causes can be as simple as an absence of excessive amount of environmental noise and light. Tetrahydrocannabinol (THC), the active component of marijuana, also causes mild vasodilatation and leads to a reddening of the eyes of marijuana users.