Because your brain needs so much blood, it's well supplied with an abundance of arteries, the blood vessels that carry oxygenated blood from your heart to your body's tissues. There are two pairs of big arteries that carry blood from your heart up to your brain:

• The internal carotid arteries, which run along the front of your neck
• The vertebral arteries, which run along the back of your neck

In the skull, the internal carotid arteries divide into several branches. The vertebral arteries unite to form the basilar artery, which then also divides into several branches. These arteries continue to branch throughout the brain, supplying fresh, oxygenated blood to all of its tissue, unless they, and other arteries located elsewhere in the body, become clogged or blocked completely by atherosclerosis.

Atherosclerosis
Atherosclerosis, or hardening of the arteries, is the underlying condition that causes ischemic stroke. Atherosclerosis begins with the formation of plaques, which are hard, fatty deposits that develop over a period of years in medium-to-large size arteries. Plaques are composed of cholesterol and other fats, calcium, inflammatory cells, and other substances.

It's theorized that plaques may be the body's attempt to heal the injured inner lining of the arteries. Arteries may be damaged by irritating substances carried in the bloodstream, like alcohol and nicotine, or by high blood pressure, high cholesterol, or certain diseases, like diabetes. Cells of the immune system and platelets, blood cells that assist in clotting, clump at the injured site in an attempt to repair it, leading to inflammation. Cholesterol and other substances in the bloodstream accumulate at the site and harden over time.

The ever-growing plaques reduce the diameter of the arteries, decreasing blood flow and increasing the amount of pressure the blood exerts against the arterial wall. To defend against the higher blood pressure, the arteries reinforce their walls, making them thicker and stiffer. This makes it even more difficult for blood to get through the arteries.

When the carotid arteries become narrowed and stiffened by atherosclerosis, the condition is called carotid artery disease.

More on this topic

What Is Stroke? (VIDEO)
Your Brain Needs Oxygen
Clogged Carotids
Degree of Blockage
Types of Stroke
Risk Factors
Symptoms, Test & Diagnosis
Treating Stroke
Life After Stroke

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