Difference Between Vasodilation and Vasoconstriction

Main Difference – Vasodilation vs Vasoconstriction

Warm-blooded animals are capable of regulating their body temperature independently from the environmental temperature. Vasoconstriction and vasodilation are the two types of mechanisms involved in the thermoregulation in the above-mentioned animals. The main difference between vasodilation and vasoconstriction is that vasodilation is the widening of blood vessels whereas vasoconstriction is the narrowing of blood vessels. Both vasodilation and vasoconstriction occur under the influence of the nervous system. Smooth muscles are responsible for both vasodilation and vasoconstriction.

Key Areas Covered

1. What is Vasodilation
       – Definition, Role, Vasodilators
2. What is Vasoconstriction
      – Definition, Role, Vasoconstrictors
3. What are the Similarities Between Vasodilation and Vasoconstriction
      – Outline of Common Features
4. What is the Difference Between Vasodilation and Vasoconstriction
      – Comparison of Key Differences

Key Terms: Blood Capillaries, Blood Vessels, Smooth Vessels, Vasoconstriction, Vasoconstrictors, Vasodilation, Vasodilators

Difference Between Vasodilation and Vasoconstriction - Comparison Summary

What is Vasodilation

Vasodilation refers to the dilation of blood capillaries near the skin while constricting the deeper blood vessels to lose heat from the body. The relaxation of smooth muscles of the blood capillaries near the skin causes vasodilation. This leads to the widening of those blood capillaries, reducing the vascular resistance to the blood flow inside the blood vessel. On that account, the blood flow through the blood capillaries near the skin increases. Other than that, the blood pressure in these blood capillaries is also reduced. The effect of vasodilation and vasoconstriction on blood capillaries is shown in figure 1.

Main Difference - Vasodilation vs Vasoconstriction

Figure 1: Cross Section of Blood Vessels

As vasodilation increases the flow of blood to the skin, it brings the internal body heat near the skin, cooling the body in high environmental temperatures. Vasodilation also enhances the entry of clotting factors and white blood cells into the damaged tissues. It increases the delivery of nutrients and oxygen throughout the body during energy-consuming activities.

Vasodilators refer to the bodily natural signals that cause vasodilation. They include parasympathetic nerve impulses, the release of hormones and bradykinin, and drugs. The drugs that cause vasodilation may be given for angina, congestive heart failure, hypertension or pulmonary hypertension.

What is Vasoconstriction

Vasoconstriction refers to the constriction of blood capillaries near the skin while dilating the deeper blood vessels for the conservation of the body heat. The constriction of the smooth muscles of the blood capillaries near the skin causes vasoconstriction. This leads to the narrowing of those blood capillaries, increasing the vascular resistance to the blood flow inside the blood vessel. Thus, the blood flow through the blood capillaries near the skin decreases. Moreover, the blood pressure also increases in these blood capillaries. The effect of the diameter of a blood vessel on blood pressure is shown in figure 2.

Difference Between Vasodilation and Vasoconstriction

Figure 2: Effect of the Diameter of Blood Vessels

Vasoconstriction decreases the blood flow to the skin, preventing the loss of metabolic heat from the body. Vasoconstriction takes place in case of an injury to a blood vessel, preventing the blood loss. It also prevents orthostatic hypotension. The sympathetic nerve impulses that cause vasoconstriction are considered as natural vasoconstrictors or vasopressors. Epinephrine, serotonin, and prostaglandins are also considered as vasoconstrictors. Cocaine, stimulants, decongestants, amphetamines, and antihistamines are the drugs that lead to vasoconstriction.

Similarities Between Vasodilation and Vasoconstriction

  • Vasodilation and vasoconstriction are two mechanisms involved in the thermoregulation in warm-blooded animals.
  • Both vasodilation and vasoconstriction are controlled by the nervous system.
  • Smooth muscles in blood vessels are responsible for both vasodilation and vasoconstriction.

Difference Between Vasodilation and Vasoconstriction

Definition

Vasodilation: Vasodilation refers to the dilation of blood capillaries near the skin.

Vasoconstriction: Vasoconstriction refers to the constriction of blood capillaries near the skin.

Diameter of Blood Vessels

Vasodilation: Vasdilaiton widens the blood capillaries near the skin while constricting the deeper blood vessels.

Vasoconstriction: Vasoconstriction narrows the blood capillaries near the skin while dilating the deeper blood vessels.

Vascular Resistance

Vasodilation: Vasodilation reduces the vascular resistance to the blood flow.

Vasoconstriction: Vasoconstriction increases the vascular resistance to the blood flow.

Blood Flow

Vasodilation: Vasodilation increases the blood flow through the vessels near the skin.

Vasoconstriction: Vasoconstriction decreases the blood flow near the skin.

Blood Pressure

Vasodilation: Vasodilation decreases the blood pressure inside the blood vessel near the skin.

Vasoconstriction: Vasoconstriction increases the blood pressure inside the blood vessel near the skin.

Caused by

Vasodilation: Vasodilation is caused by the increasing temperature in the environment.

Vasoconstriction: Vasoconstriction is caused by the decreasing temperature in the environment.

Nerve Impulses

Vasodilation: Vasodilation is caused by the parasympathetic nerve impulses.

Vasoconstriction: Vasoconstriction is caused by sympathetic nerve impulses.

Other Reasons

Vasodilation: Vasodilation is caused by noradrenaline, histamine, prostaglandin, niacin, and rising levels of carbon dioxide.

Vasoconstriction: Vasoconstriction is caused by epinephrine, insulin, antidiuretic hormone, and low oxygen levels.

Role

Vasodilation: Vasodilation leads to the loss of body heat to the surroundings through conduction, convection, and radiation.

Vasoconstriction: Vasoconstriction conserves body heat.

Conclusion

Vasodilation and vasoconstriction are two mechanisms mainly involved in the thermoregulation of the warm-blooded animals. Blood capillaries near the skin are dilated and the deeper vessels are constricted in vasodilation, losing the body to the surroundings. Blood capillaries near the skin are constricted and the deeper vessels are dilated in vasoconstriction, conserving the body heat. The main difference vasodilation and vasoconstriction is the effect of each mechanism on blood vessels.

Reference:
1. “Vasodilation and Vasoconstriction”, NORMALBREATHING.com, Available here.
Image Courtesy:
1. “Vasoconstriction and Vasodilation” By Elizabeth2424 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Blausen 0092 BloodPressureFlow” By Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014″. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work (CC BY 3.0) via Commons Wikimedia

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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