11 Striking Facts About the Jugular


The human body is an amazing thing. For each one of us, it's the most intimate object we know. And yet most of us don't know enough about it: its features, functions, quirks, and mysteries. Our series The Body explores human anatomy, part by part. Think of it as a mini digital encyclopedia with a dose of wow.

Jugular veins are popular in horror flicks for their gushing at the mouths of vampires, werewolves, and knife-wielding assassins. While that's unlikely to happen to most of us, this crucial vein does give up copious blood. Jugular veins are big—much larger than the veins you typically offer to your doctor for a blood test and those you find spidering off the side of your legs. Jugular veins are also key players in the circulation and drainage systems to the brain, face, and neck. To learn more, Mental Floss spoke with William W. Ashley, a cerebral-vascular neurosurgeon at Sandra and Malcolm Berman Brain & Spine Institute at LifeBridge Health Hospital, in Baltimore, Maryland. Here are 11 things you might not have known about this crucial body part.


"The jugular vein is an important body part because it drains deoxygenated blood from the head and the neck," Ashley tells Mental Floss. "Most important is to drain the brain. If you block the jugular veins, the pressure in the brain goes up."


There's an internal and an external jugular vein on each side of the neck. The internal jugular vein (really a pair of veins) largely drains the cerebral veins—those coming from the brain—while the external jugular vein (also a pair) drains those structures more on the surface of the head, such as the scalp, sinuses, and other portions of the face. The left vein is usually smaller than the one on the right, but both possess valves that help transport blood. At two points in the vein it looks wider, and these parts are called the superior bulb and the inferior bulb.


Your jugular veins run alongside the thyroid gland down to just above your collarbone, and close to your trachea, or windpipe. When you're picking up a heavy box, or clenching your jaw, your jugular veins might bulge slightly. "They respond to changes in pressure, so you can see them get big and small," Ashley says.


According to the Indian Journal of Plastic Surgery, during a surgery to treat a 65-year-old woman's cancer of the tongue, surgeons discovered a surprise: She had two right internal jugular veins, "a rare congenital abnormality," the authors write. While unusual, it didn't appear to cause any other health problems.


Ashley had a patient with the opposite issue: "I've seen an absence of one [right vein] where everything drained on the left side. We found it incidentally. If she injured her one jugular vein, she'd be in bad shape. We were doing an angiogram to see if she had a brain aneurism." Her dearth of jugulars hadn't caused any health problems, however, he said, because "the body had adopted a different pattern [of drainage]."


A bulging or "distended" jugular vein can be a sign of emergency. Unless you're The Hulk, that distended vein is a sign that the jugular is carrying more blood than the heart has the ability to pump back out. The conditions that can cause this include tension pneumothorax—where air has leaked from the lungs into the chest cavity and can't get back out without being released by a needle—or cardiac tamponade, a condition where fluid leaks from the heart into the pericardium, the sac that surrounds the heart. In this case, pericardiocentesis is required—drawing the fluid out through a needle. Lastly, constrictive pericarditis, an infection of the pericardium, can also cause this condition, which may require surgery and antibiotics to treat.


A blood clot in the internal jugular veins (IJV), known as a thrombosis, is a very serious condition that can prove fatal if not caught and treated quickly. Clots in the IJV are rare compared to those that occur in legs and lungs, but they can happen. Most commonly they are the result of an infection or a tumor. In a very small number of cases, in vitro fertilization (IVF) treatments, in which a woman receives hormones and drugs to stimulate ovulation to increase chances of pregnancy, can cause a thrombosis of the IJV. This seems to be related to ovarian hyper stimulation syndrome (which can occur in an IVF cycle), where swelling and inflammation of the ovaries also causes blood leaving the ovaries to become hypercoagulated, or extra thick. This thickened blood can then form a clot in the IJV. Any thrombosis is treated with anticoagulation medicines, and if infection is present, antibiotics.


"One interesting thing about them is that they can cause a variety of brain problems, such as elevated pressure in the brain," says Ashley. One is a condition known as Eagle syndrome, which he calls "pretty cool" (as only a cerebral-vascular neurosurgeon could). In this syndrome, "a congenital bony prominence at the base of skull pushes on the jugular vein and causes the brain to swell up and become engorged with blood," Ashley describes. As the pressure builds in the brain, it has to be surgically released or it will cause serious damage. "We can do that by putting in a shunt [in the brain] to drain off fluid," he says. Occasionally, doctors can also surgically remove the piece of the bone that's causing the problem.


Other than congenital issues—those you're born with—the most common causes of constriction in the jugular veins are from traumas, such as car accidents and other traumatic brain or neck injuries. "Blood clots and trauma can constrict the jugular vein," Ashley says, as can "congenital narrowing of the vein."


In the past five to 10 years, surgeons have begun to use stents, metal tubes inserted directly into the vein, to open it up. "A shunt is a tube that goes into the brain that helps drain off spinal pressure. The stent goes into the vein, that's a little more elegant a solution," Ashley says.


If your jugular is punctured, Ashley warns, "you can rapidly lose blood." A needle is less likely to cause problems than a knife, but blood is likely to flow out of your jugular "more rapidly than out of a vein in wrist or arm," making a puncture a serious problem.

Why Can You Sometimes See Your Breath?

Chalabala/iStock via Getty Images
Chalabala/iStock via Getty Images

The human body is made up of about 60 percent water, meaning that when we breathe, we don’t just exhale carbon dioxide—we also exhale a certain amount of water vapor.

Water molecules need a lot of energy in order to remain in a gaseous form. When the warm water vapor molecules from your lungs reach colder air, they condense into “tiny droplets of liquid water and ice,” according to Wonderopolis. In fact, this process of condensation is also how clouds are formed.

But it’s actually relative humidity, not just temperature, that determines whether you can see your breath. The water vapor in your breath condenses into a liquid when it hits dew point—the temperature at which the air is saturated and can’t hold any more water in gas form. Since cold air can’t hold as much water vapor as warm air, you're much more likely to see your breath on a chilly day, but that's not always the case.

On more humid days, you may be able to see your breath even when it’s relatively warm outside. That’s because the air is already more saturated, making the dew point higher. And on especially dry days, even if it's cold outside, you may not be able to see your breath at all. Dry, unsaturated air can hold more water vapor, so you can huff and puff without seeing any evidence of it at all.

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7 Facts About Blood

Moussa81/iStock via Getty Images
Moussa81/iStock via Getty Images

Everyone knows that when you get cut, you bleed—a result of the constant movement of blood through our bodies. But do you know all of the functions the circulatory system actually performs? Here are some surprising facts about human blood—and a few cringe-worthy theories that preceded the modern scientific understanding of this vital fluid.

1. Doctors still use bloodletting and leeches to treat diseases.

Ancient peoples knew the circulatory system was important to overall health. That may be one reason for bloodletting, the practice of cutting people to “cure” everything from cancer to infections to mental illness. For the better part of two millennia, it persisted as one of the most common medical procedures.

Hippocrates believed that illness was caused by an imbalance of four “humors”—blood, phlegm, black bile, and yellow bile. For centuries, doctors believed balance could be restored by removing excess blood, often by bloodletting or leeches. It didn’t always go so well. George Washington, for example, died soon after his physician treated a sore throat with bloodletting and a series of other agonizing procedures.

By the mid-19th century, bloodletting was on its way out, but it hasn’t completely disappeared. Bloodletting is an effective treatment for some rare conditions like hemochromatosis, a hereditary condition causing your body to absorb too much iron.

Leeches have also made a comeback in medicine. We now know that leech saliva contains substances with anti-inflammatory, antibiotic, and anesthetic properties. It also contains hirudin, an enzyme that prevents clotting. It lets more oxygenated blood into the wound, reducing swelling and helping to rebuild tiny blood vessels so that it can heal faster. That’s why leeches are still sometimes used in treating certain circulatory diseases, arthritis, and skin grafting, and helps reattach fingers and toes. (Contrary to popular belief, even the blood-sucking variety of leech is not all that interested in human blood.)

2. Scientists didn't understand how blood circulation worked until the 17th century.

William Harvey, an English physician, is generally credited with discovering and demonstrating the mechanics of circulation, though his work developed out of the cumulative body of research on the subject over centuries.

The prevailing theory in Harvey’s time was that the lungs, not the heart, moved blood through the body. In part by dissecting living animals and studying their still-beating hearts, Harvey was able to describe how the heart pumped blood through the body and how blood returned to the heart. He also showed how valves in veins helped control the flow of blood through the body. Harvey was ridiculed by many of his contemporaries, but his theories were ultimately vindicated.

3. Blood types were discovered in the early 20th century.

Austrian physician Karl Landsteiner discovered different blood groups in 1901, after he noticed that blood mixed from people with different types would clot. His subsequent research classified types A, B and O. (Later research identified an additional type, AB). Blood types are differentiated by the kinds of antigens—molecules that provoke an immune system reaction—that attach to red blood cells.

People with Type A blood have only A antigens attached to their red cells but have B antigens in their plasma. In those with Type B blood, the location of the antigens is reversed. Type O blood has neither A nor B antigens on red cells, but both are present in the plasma. And finally, Type AB has both A and B antigens on red cells but neither in plasma. But wait, there’s more! When a third antigen, called the Rh factor, is present, the blood type is classified as positive. When Rh factor is absent, the blood type is negative.

Scientists still don’t understand why humans have different blood types, but knowing yours is important: Some people have life-threatening reactions if they receive a blood type during a transfusion that doesn’t “mix” with their own. Before researchers developed reliable ways to detect blood types, that tended to turn out badly for people receiving an incompatible human (or animal!) blood transfusion.

4. Blood makes up about 8 percent of our total body weight.

Adult bodies contain about 5 liters (5.3 quarts) of blood. An exception is pregnant women, whose bodies can produce about 50 percent more blood to nourish a fetus.)

Plasma, the liquid portion of blood, accounts for about 3 liters. It carries red and white blood cells and platelets, which deliver oxygen to our cells, fight disease, and repair damaged vessels. These cells are joined by electrolytes, antibodies, vitamins, proteins, and other nutrients required to maintain all the other cells in the body.

5. A healthy red blood cell lasts for roughly 120 days.

Red blood cells contain an important protein called hemoglobin that delivers oxygen to all the other cells in our bodies. It also carries carbon dioxide from those cells back to the lungs.

Red blood cells are produced in bone marrow, but not everyone produces healthy ones. People with sickle cell anemia, a hereditary condition, develop malformed red blood cells that get stuck in blood vessels. These blood cells last about 10 to 20 days, which leads to a chronic shortage of red blood cells, often causing to pain, infection, and organ damage.

6. Blood might play a role in treating Alzheimer's disease.

In 2014, research led by Stanford University scientists found that injecting the plasma of young mice into older mice improved memory and learning. Their findings follow years of experiments in which scientists surgically joined the circulatory systems of old and young mice to test whether young blood could reverse signs of aging. Those results showed rejuvenating effects of a particular blood protein on the organs of older mice.

The Stanford team’s findings that young blood had positive effects on mouse memory and learning sparked intense interest in whether it could eventually lead to new treatments for Alzheimer’s disease and other age-related conditions.

7. The sight of blood can make people faint.

For 3 to 4 percent of people, squeamishness associated with blood, injury, or invasive medical procedures like injections rises to the level of a true phobia called blood injury injection phobia (BII). And most sufferers share a common reaction: fainting.

Most phobias cause an increase in heart rate and blood pressure, and often muscle tension, shakes, and sweating: part of the body’s sympathetic nervous system’s “fight or flight” response. But sufferers of BII experience an added symptom. After initially increasing, their blood pressure and heart rate will abruptly drop.

This reaction is caused by the vagus nerve, which works to keep a steady heart rate, among other things. But the vagus nerve sometimes overdoes it, pushing blood pressure and heart rate too low. (You may have experienced this phenomenon if you’ve ever felt faint while hungry, dehydrated, startled, or standing up too fast.) For people with BII, the vasovagal response can happen at the mere sight or suggestion of blood, needles, or bodily injury, making even a routine medical or dental checkup cause for dread and embarrassment.