Vasoconstriction: when the blood vessels constrict
Vasoconstriction is a physiological mechanism that causes the diameter of the body’s blood vessels to decrease by contraction of the muscles that make up the lining of the blood vessels (arteries, veins). It can be caused for several reasons and factors, but in any case for an immediate response to a necessary adaptation, in particular to stop a bleeding.
What is vasoconstriction?
Vasoconstriction is a natural process consisting in reducing the diameter of the blood vessels, by contraction of its muscle fibers. Its opposite action corresponds to vasodilation; both movements encompass what is called vasomotricity.
Vasoconstriction has the utility of limiting, for example, bleeding when a lesion of a blood vessel appears. This is the first phase of hemostasis. The vasoconstrictor nerve centers are at the origin of this mechanism, but also the hormones angiotensin, adrenaline and noradrenaline. Vasoconstriction thus causes a decrease in blood flow in the organ in question. The surfaces of the vessel will then stick together, they become adhesive.
What are the causes of vasoconstriction?
There are several factors that trigger vasoconstriction in the body. The most common is damage to muscle cells, whose blood vessels, by constricting, will stop the bleeding.
Certain substances also cause this tightening:
- Serotonin, released by platelets;
- Activation of pain receptors passing through the nervous system (catecholamines, adrenaline, noradrenaline);
- Certain toxins or foods present in food (caffeine for example).
Beyond these first causes, the vasoconstriction mechanism can be set up during the regulation of heat exchanges in the body, involving the nervous, endocrine, cardiac and respiratory systems.
When the body temperature drops, during very cold weather for example, one can observe the appearance of cutaneous vasoconstriction: this phenomenon makes it possible to isolate the peripheral tissues of the center of the body. The narrowing of the diameter of the blood vessels at the periphery of the body has the effect of recreating a “gradient” (difference) in temperature between the skin and the organs of the heart, lungs, brain, kidneys. Accompanied by arterial hypertension and an increase in the tone of the nervous system, this vasoconstriction thus increases the heart rate. This leads to a 10% increase in the plasma concentration of red and white blood cells, platelets, but also cholesterol and fibrinogen. Consequence: an increase in blood viscosity around 20%.
In conclusion, when your body is subjected to the cold, the internal thermostat turns on automatically and burns a fairly large amount of energy. Heart requirements and oxygen requirements also increase.
Also, stress can also be responsible for activating vasoconstriction. By the action of adrenaline, sending a punctual stress message, the vessels will operate to tighten their diameter, momentarily.
Nicotine causes vasoconstriction in the arteries, reducing blood flow, and therefore the amount of oxygen supplied to the tissues and toxins eliminated from the same tissues.
This vasoconstriction is reversible and disappears a few hours after smoking. Vasoconstriction becomes permanent during the day, for high dose smokers.
Finally, vasoconstriction can be a sign of potential disease, intoxication or envenomation. For example, Raynaud’s syndrome is manifested by excessive vasoconstriction of the small vessels in the extremities of the body (hands, feet), particularly during cold weather or stress. This disease causes loss of blood supply to the affected area and pain when blood flow returns to those same areas.
Vasoconstriction can be caused by drug treatment, in order to limit certain bleeding in specific situations.
What about vasodilation?
This vascular movement is the opposite effect of vasoconstriction and therefore corresponds to an increase in the size of the vessels by dilation.
This dilation is made possible by the relaxation of the muscles surrounding the blood vessels.
The causes of vasodilation are:
- The heat ;
- Illness, poisoning, envenomation;
- Allergic, inflammatory reaction (edema);
- Alcohol has a vasodilator effect and dilates the blood vessels in the brain;
- Caused by a drug, such as hypertensive drugs.
In the latter case, a hypertensive person has vessels that are too “narrow” for the blood pressure exerted on their veins, damaging them. We will therefore use a drug to dilate its vessels in order to reduce blood pressure.