What Is the Function of Arterioles?

How Blood Vessels Play a Unique Role In Blood Pressure

Illustration of a capillary system with metarterioles and precapillary sphincters, as is present in the mesenteric microcirculation.
Wikimedia Commons

Arteries are the blood vessels that carry oxygenated blood away from the heart. As they move down through the arterial network, they get smaller and smaller like the branches and twigs of a tree. When they have decreased in size to a certain point, we refer to them as arterioles.

Arterioles share many of the properties of arteries. They are strong, have a relatively thick wall, and contain a high percentage of smooth muscle.

But they also serve another important function. Arterioles are the most highly regulated blood vessels in the human body and contribute the most to the rise and fall of blood pressure.

As a group, arterioles respond to a wide variety of chemical and electrical messages from the brain, immune system, and endocrine system and are constantly changing in size in response to those messages. By doing so, the blood flow can either speed up or slow down, causing relative changes in the blood pressure.

Tracing the Blood Flow to the Arterioles

The circulatory system is considered a closed system insofar as the blood never leaves the confines of the vascular network. At its most basic, the system is a loop which starts and ends at the heart, distributing oxygen molecules on the outward journey and carrying carbon dioxide back on the inward journey.

The outward route begins as the heart pumps blood through the aorta and continues pumping as the blood makes it way to the smallest of blood vessels called capillaries.

But, before this, the blood must pass through the arterioles where its speed is constantly being adjusted and regulated. These adjustments can occur for any number of reasons, including a rise or fall in temperature, physical activity, food, stress, or exposure to toxins or medications.

Whatever the cause, this change can directly impact a person’s blood pressure.

A constriction of the arterioles can cause the blood pressure rise while the relaxing of the arterioles can cause it to fall. The aim, ultimately, is to regulate blood pressure so that remains steady and less prone to fluctuation.

As a result of this action, the blood will no longer be moving in a pulsing fashion as it reaches the capillaries. Instead, the flow will be more continuous, allowing for the steady exchange of oxygen and carbon dioxide molecules. Once the exchange is complete, the blood will make the inward journey through the network of veins, finally returning to the heart through the inferior and superior vena cava.

Conditions That Can Affect Arteriole Action

When the body is functioning at it should, the arterioles help ensure that the blood pressure remains within normal, healthy limits. However, there are conditions that can affect or impede their performance. Among them:

  • Arteriosclerosis is the thickening, hardening, and loss of elasticity of the arterial walls. This process restricts the arteriole’s ability to regulate blood flow and allows the progressive buildup of plaque and cholesterol on the arterial walls.
  • Arterial stenosis is the abnormal narrowing of the arteries. This can be caused by any number of things including pollution, smoking, diabetes, infection, and birth defects. The persistent constriction of vessels due to pollutants or chronic infection can lead to the progressive scarring (fibrosis) of arterial tissue.
  • Arteritis is inflammation of the arterial walls in and around the scalp, often associated with autoimmune diseases.
  • Meanwhile, medications called antihypertensives are used to relax the arterial walls thereby lowering the overall systemic pressure.

Source:

Nobel, A.; Johnson, R.; Bass, P. et al. (2010) The Cardiovascular System. London: Churchill Livingstone/Elsevier.

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