The Function of Arterioles in Blood Pressure

How the Specialized Vessels Regulate Blood Pressure

A blood pressure monitor.
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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 of a tree. When they have decreased in size to less than 300 micrometers (µm), we refer to them as arterioles.

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

But, they also serve another important function. Arterioles are, in fact, the most highly regulated blood vessels in the 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

The circulatory system is considered closed 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 the capillaries.

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

The function of the arterioles, therefore, is to regulate blood pressure so that it remains steady and less prone to fluctuation.

By doing so, the blood will no longer be pulsing 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.

Arteriole Disorders

When the body is functioning as it should, the arterioles help ensure that the blood pressure remains within normal, healthy limits. However, there are conditions that may 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 for the progressive buildup of plaque and cholesterol on the arterial walls. The three main causes of arteriosclerosis are high cholesterol, high triglycerides, cigarette smoking, and even high blood pressure itself.
  • 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. More specifically, the persistent constriction of blood vessels due to pollutants or chronic infection can lead to the progressive scarring (fibrosis) of arterial tissue.
  • Arteritis is the inflammation of the arterial walls in and around the scalp, often associated with autoimmune diseases. The inflammation of the arterial walls leads to a decrease in blood flow. A prime example is giant cell arteritis (GCA) which affects the branches of the external carotid artery of the neck. With GCA, the impaired blood flow can cause symptoms of​ a headache, vision changes, vision loss, and jaw pain when chewing.

A Word From Verywell

If you have been diagnosed with high blood pressure, you need to seek the care of a doctor who can place you on antihypertensive medications. While you may feel well and have no symptoms, the very presence of high blood pressure can increase your risk of heart attack and stroke.

It is why high blood pressure is rightly called the "silent killer."

Sources:

Lehmann, M. and Schmieder, R. "Remodeling of retinal small arteries in hypertension," Am J Hypertens. 2011; 24(12):1267-73. DOI: 10.1038/ajh.2011.166.

Nobel, A.; Johnson, R.; Bass, P. et al. (2010) The Cardiovascular System (Second Ed.). London: Churchill Livingstone/Elsevier. ISBN: 9780702050824.