Circulatory System
Your circulatory system is composed of no fewer than 65,000 miles of blood vessels, arteries, veins, and capillaries, some as wide as a garden hose, some so fine that it would take ten of them lying side by side to form the thickness of a human hair. Together they transport about 6 qts of blood throughout your entire body at the dizzying rate of three times every minute. Arteries carry blood away from the heart to the capillaries, where nutrients and oxygen flow out into the tissues. The veins collect the de-oxygenated blood from the capillaries and carry it back to the heart for replenishment. Because your blood vessels need to work under powerful pressure, they're normally strong, flexible, and resilient.

Aneurysms
But sometimes an artery can develop an aneurysm, a bulge in a weak area of the artery caused by the pressure of the blood inside the vessel, something like a bulge in an over-inflated inner tube. Typically aneurysms occur where the vessel branches.

You might live with an aneurysm your entire life and never know it was there. Aneurysms can be small and slow growing, or they may be large, over 2-1/4 inches (5.5 cm). Brain, or cerebral, aneurysms are considered to be giant if they are over 1 inch (2.5 cm). Most aneurysms never rupture. Large, fast-growing aneurysms are the most dangerous because they are the most likely to rupture. When they do, they can be life threatening.

More on this topic

What is an Aneurysm? (VIDEO)
Aneurysms Explained
Where Aneurysms Happen
Head & Neck Aneurysms
Risk Factors
Symptoms, Tests, and Diagnosis
Aneurysm Complications
Abdominal Aortic Aneurysm Surgery
Cerebral Aneurysm Surgery
Prevention

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