When people think of the body's circulatory system, the first thing that usually comes to mind is the heart. But the heart couldn't do its job without blood vessels: a vast system of elastic tubes made of muscle. This network of vessels carries blood to every part of your body, ensuring that your heart, lungs, and all vital organs get the oxygen and nutrients they need, the National Heart, Lung, and Blood Institute (NHLBI) explains.

Here are 10 amazing facts about blood vessels:

1. Your blood vessels could circle the globe. Though blood vessels are relatively small, the network is amazingly long. In fact, if they were laid out in a line, they would measure more than 60,000 miles in length, the U.S. National Institute on Aging (NIA) calculates. Considering that the circumference of the Earth is 24,873.6 miles, according to NASA, that means your blood vessels could circle the globe more than twice.

2. They carry a million barrels of blood in a lifetime. The blood in your body is continuously flowing. Every day, your heart pumps about 1,800 gallons of blood through your blood vessels, the NIA states. Over the course of a lifetime, this vast system carries about a million barrels of blood throughout the body.

3. Blood vessels work as a team. The three major types of blood vessels – arteries, veins, and capillaries – all work together, according to the NHLBI. When the heart contracts, blood is pumped into arteries that carry it away from the heart. Arteries are connected to tiny, thin-walled blood vessels called capillaries, which allow oxygen to move from the blood into the cells of the body. Then veins carry deoxygenated blood back to the heart.

4. Serious conditions can affect all types of blood vessels. Most people are aware of health conditions that plague larger blood vessels, from atherosclerosis (hardening of the arties) to varicose veins. But even tiny capillaries can be affected. Capillary leak syndrome is a rare disease in which the walls of these tiny blood vessels leak, flooding surrounding tissues with blood. It can lead to severe swelling and dangerously low blood pressure, according to the National Institutes of Health.

5. Blood vessels act as a force field for the brain. Blood vessels are part of an important defense system known as the blood-brain barrier. A network of blood vessels and tissue comprised of closely-spaced cells helps keep harmful substances from reaching the brain, the National Cancer Institute explains. The blood-brain barrier allows some essential substances, such as water, oxygen, and carbon dioxide, to pass into the brain, but keeps bacteria and other dangerous substances out. Although general anesthetics can pass through the blood-brain barrier, many important medications, including some anti-cancer drugs, are unable to, presenting challenges for doctors treating many serious and debilitating diseases that affect the brain, the NCI notes. These include brain cancer and Parkinson's disease.

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6. Blood vessels are affected by the weather. The circulatory system helps maintain body temperature. Blood vessels expand to release heat, allowing you to cool down, and narrow or constrict to conserve heat, according to the National Library of Medicine. In extreme cases, such as when your feet are exposed to very cold or wet conditions for prolonged periods of time — a condition called trench foot — the constriction of blood vessels can shut down circulation, causing skin tissue to die, according to the U.S. Centers for Disease Control and Prevention. Another consequence of extreme exposure is frostbite, which can happen after just a few minutes in freezing conditions.

7. Blame that ice cream headache on your blood vessels. Anyone who likes popsicles or ice water may be familiar with the uncomfortable sensation known as brain freeze. When something cold touches the warm roof of your mouth, local blood vessels constrict to minimize heat loss, then relax to restore blood flow. This response triggers a burst of pain that lasts for a few minutes, or until the body adapts to the sudden change in temperature, the National Institute of Neurological Disorders and Stroke explains. The agency notes that ice cream headaches are more common among people who have migraines.

8. Your blood vessels might get a boost from chocolate. Eating moderate amounts of chocolate could offer some benefits, including keeping your heart and blood vessels healthy and helping to lower heart disease and stroke risk, according to a June 2015 study published in Heart. How does this guilty pleasure benefit your blood vessels? Chocolate, particularly dark chocolate, contains micronutrients called flavonoids that are believed to have strong antioxidant properties, the American Institute for Cancer Research points out.

9. Obesity takes a toll on the blood vessels. It's estimated that every pound of fat requires about one extra mile of blood vessels, according to the Obesity Action Coalition – and that means more work for the heart. This could put added strain on the heart, notes David Zhao, MD, section chief and professor of cardiology at Wake Forest Baptist Medical Center in Winston-Salem, North Carolina. "Obesity has a threshold phenomenon," Dr. Zhao explains. For someone who weighs 110 pounds, a one-pound gain isn't going to cross the threshold and put a lot of strain on the heart and blood vessels. But for someone who is already 300 pounds, it can put a burden on the heart and increase the risk for blockages inside blood vessels, he cautions.

10. Blood vessel damage can start early. Blood vessels undergo changes with age and time, but damage can start early, even during childhood, Zhao warns. Obese teens with high blood pressure may show signs of thicker arteries by the time they are 30 years old, the American Heart Association reports. Exposure to tobacco smoke causes immediate damage not only to the lungs, but also to blood vessels throughout the body. Smoking can cause scar tissue and fats to accumulate inside blood vessels, restricting blood flow, according to the American Lung Association. Over the course of a lifetime, these insults take a cumulative toll on the blood vessels, Zhao adds. He points out that exercising regularly, eating a healthy diet, maintaining a healthy weight, and not smoking are key lifestyle changes that can help protect your blood vessels.