CLOSE
iStock
iStock

11 Amazing Facts About Veins

iStock
iStock

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.

Beneath your skin, and deeper within your body, run networks of veins. These thin, tube-like structures are an essential part of the circulatory system, which distributes blood and nutrients throughout the body. What Thomas E. Eidson, a phlebologist (vein disease specialist) at Atlas Vein Care in Arlington, Texas, finds most compelling about veins is "how absolutely intricate and fragile the circulatory system can seem and yet at the same time be so resilient and adaptive."

1. VEINS ARE ONE OF THREE KINDS OF BLOOD VESSELS.

Three types of blood vessels make up the human circulatory system: arteries, veins, and capillaries. All three of these vessels transport blood, oxygen, nutrients, and hormones to organs and cells. While arteries carry oxygenated blood away from the heart to the tissues of the body, veins carry oxygen-depleted blood from the tissues back to the heart, and in fact have special valves that help them to achieve this directional flow. Capillaries are tiny blood vessels that connect arteries to veins and allow nutrients in the blood to diffuse to the body's tissues.

2. A SINGLE VEIN IS COMPRISED OF THREE LAYERS.

Veins, small as they are, consist of three layers. According to Eidson, these layers are known as the tunica adventitia, tunica media, and tunica intima. The tunica adventitia is the tough outer layer of arteries and veins and is made mainly of connective tissues. The middle layer, tunica media, is all smooth muscle and elastic fibers. This layer is thinner in veins than in arteries. The innermost layer, tunica intima, comes in direct contact with blood as it flows through the vein. This structure is made up of smooth cells and has a hollow center known as the lumen.

3. OUR BODIES CONTAIN UP TO 100,000 MILES OF BLOOD VESSELS.

All the arteries, veins, and capillaries of a human child, stretched end to end, are estimated to wrap around the Earth about 2.5 times (the equivalent of about 60,000 miles). The amount of blood vessels in a human adult would circle our planet four times, equaling 100,000 miles, according to Eidson.

4. CAPILLARIES ARE SMALLER THAN THE WIDTH OF A HUMAN HAIR.

Capillaries are tiny—at their smallest, they're less than a third of the thickness of a human hair. But to really put it into perspective, consider that when red blood cells flow through capillaries, "[they] must travel through them one cell at a time in a single-file line," Eidson says.

5. PHYSICIANS HAD THE CIRCULATORY SYSTEM ALL WRONG UNTIL THE 17TH CENTURY.

"Physicians followed an incorrect model of the circulatory system proposed by Greek physician and philosopher Galen of Pergamon from about the 2nd century CE until the 1600s," Eidson says. According to a paper in the Journal of Thrombosis and Haemostasis, Galen thought there were two systems: one in which the liver, not the heart, produced blood that was distributed in the body centrifugally, and another where arteries carried air from the lungs and more blood to tissues. "Blood was not seen to circulate but rather to slowly ebb and flow," author W.C. Aird wrote. This attitude prevailed until 1628, when English physician William Harvey first correctly described the circulatory system and the function of the heart.

6. THE BODY CAN FORM NEW VESSELS WHEN ONE IS BLOCKED.

Eidson says the body can form new blood vessels if a pathway gets blocked, a process called angiogenesis or neovascularization. On the positive side, this is the process by which flesh wounds heal, drawing nutrients and oxygen from the nearest healthy capillaries to the site of those that are damaged; this isn't too hard given how numerous capillaries are in the body. On the negative side, this same process can lead to corneal neovascularization, in which new blood vessels invade the cornea from the limbus, a part of the eye where the cornea meets the sclera—the white part of the eye. The extra blood vessels can cause inflammation and scarring of the cornea, and even result in blindness.

7. ONE PHYSICIAN PERFORMED A PIONEERING EXPERIMENT ON VEINS IN THE ARM—HIS OWN.

German physician Werner Forssmann performed a cardiac catheterization on himself in 1929. In this procedure, a thin tube called a catheter is inserted into one of the large blood vessels in the arm that leads to the heart. The medical community at the time believed studying the heart was highly unorthodox, but Forssmann was determined to prove them wrong. If the procedure succeeded, Forssmann would be able to show that a catheter could assess the pressure in the organ and how well the heart is working.

He made an incision on the inside of his left elbow and threaded the thin tube into his heart—and had a technician take an X-ray to prove the penetration was a success. Then he calmly removed the catheter from his arm with no side effects. Now, "it's a procedure performed in the U.S. approximately 1 million times per year," Eidson says. Forssmann also went on to win the Nobel Prize for Medicine in 1956, shutting up his detractors.

8. STRONG VEINS ARE ESSENTIAL TO A STRONG BODY.

Veins return oxygen-depleted blood back to the heart against the force of gravity. "If veins are too weak—a condition called venous insufficiency—blood can pool in the legs and skin causing swelling, pain, discoloration, and wounds," says Albert Malvehy, a venous and lymphatic specialist and phlebology sonographer in Delray Beach, Florida. Chronic venous insufficiency is more common in people who are obese, pregnant, or who have a family history of the problem. It can also be caused by high blood pressure in the leg veins, as a result of sitting or standing for long stints; not enough exercise, smoking, or deep vein thrombosis (blood clots). Depending on the severity, treatments may range from medication to surgery.

9. VARICOSE VEINS ARE CAUSED BY DAMAGED VALVES.

When venous valves are damaged, blood can flow in the wrong direction and lead to stretched-out, bulging veins, Gregory P. Kezele, the medical director of Vein Clinics of Cleveland, tells Mental Floss. Varicose veins, which can range in color from purplish to neutral, appear twisted and gnarled, and may be raised on the skin's surface. (Don't confuse them with spider veins, which are clusters of bluish or reddish veins near the surface of the skin that resemble webs, hence the name.) Conditions like pregnancy, obesity, and genetic predisposition can cause them. Once varicose veins appear—usually on the legs—they require a medical procedure to get rid of them.

Veins are a critical part of normal circulation in the body, so varicose veins can be more than just a cosmetic issue. "They can be a sign of a deeper circulation problem," Malvehy says. "People with varicose veins, leg pain, restless legs syndrome, leg wounds, and leg swelling should be checked by a vein specialist."

One in five people have vein disease. As recently as 10 years ago, there were few treatments to offer varicose vein sufferers except for vein stripping surgery, in which problematic veins are removed. Malvehy says that over the past decade, "there has been a revolution in treatment, such that almost all vein issues can be treated in the office with no downtime."

One common treatment is sclerotherapy, in which a liquid solution is forced into the bulging vein to stop the flow of blood. The vein will eventually turn into scar tissue and fade away, though follow-up treatments might be needed.

Another treatment is thermal ablation, performed using ultrasound guidance. Kezele explains that a physician will insert a small catheter into the diseased veins, which then delivers heat; the heat will close off blood flow to the problem veins and improve circulation as blood diverts to healthy veins.

10. AN EARLY DEPICTION OF VEIN DISEASE APPEARS IN A SCULPTURE FROM 340 BCE.

According to Kezele, the first depiction of vein disease appears on a Greek tablet dating to the 4th century BCE. The carving, from the sanctuary of Amynos, shows a man clutching a giant, disembodied leg with a bulging vein. Kezele suggests on his website that "it shows the Greek official Lysimachides dedicating a fake leg suffering from a varicose vein to Amynos," an Athenian hero revered as a healer.

11. VEINS MIGHT "POP OUT" WHEN YOU EXERCISE.

There are lots of theories on why athletes often have big, bodaciously bulging veins visible on their arms or legs after they work out. The ropy look is completely normal and temporary. Writing in Scientific American, physiology professor Mark A. W. Andrews said that a likely cause of protruding veins is arterial blood pressure during exercise. Blood that would otherwise be resting in capillaries is forced out by the pressure into the surrounding muscle. That process—called filtration—makes the muscles swell, which pushes nearby veins closer to the skin's surface so they take on a bulging appearance. The process is more noticeable in athletes and body builders with very little subcutaneous fat.

arrow
The Body
11 Amazing Facts About the Nipple

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.

Despite its relatively small size on the human body, the nipple gets a lot of attention. Biologically, the nipple serves two key functions: In women, nipples deliver milk out of the ducts within the breast to babies, and for women and men, they serve as erogenous zones. Check out our list of fascinating facts about this often-misunderstood body part.

1. THE NIPPLE HAS ITS OWN SWEAT GLANDS.

The nipple is the raised bump or protrusion on top of the breast that sits on the circular area known as the areola. The areola is often much larger in circumference than the actual nipple, as it holds small sweat glands called Montgomery glands (named for William Fetherstone Montgomery, an Irish obstetrician who first described them). The sole function of these glands is to secrete fluids during breastfeeding to lubricate the nipple and to produce a scent that attracts the baby to its mother's breast.

2. NIPPLES CAN POKE IN OR OUT.

Not all nipples point jauntily outward. Men's and women's nipples can be inverted, essentially pointing inward. In the worst-case scenario, "the skin adheres to itself and has to peel open to [turn outward] initially, and [that] can be painful," Constance Chen, a board-certified plastic surgeon and clinical assistant professor of plastic surgery at Weill Cornell Medical College in New York, tells Mental Floss. For most women, however, an inverted nipple causes neither pain nor prevents breastfeeding with proper technique or nipple shields.

3. SOME PEOPLE HAVE EXTRA NIPPLES.

While most people have two nipples, one atop each breast (yes, both women and men have breasts), some people have extra or "supernumerary" nipples outside of the typical location. One Indian man was even found to have seven.

Leigh Anne O'Connor, a certified lactation consultant in New York, says these extra nipples can appear on or below an area named the Tail of Spence (after Scottish surgeon James Spence), which extends from the breast up into the armpit.

"Some people have nipples in their armpits, or even tiny breasts, and these nipples may leak," O'Connor tells Mental Floss. But an extra nipple is just an extra nipple—no cause for alarm or shame.

4. HERE'S WHY MEN HAVE NIPPLES.

Since the main purpose of nipples is breastfeeding babies, and male breasts do not lactate, it begs the question: Why do men have nipples? Scientists Stephen Jay Gould and Richard C. Lewontin tried to get to the bottom of this conundrum in a seminal paper in 1993.

All human embryos start out essentially the same. If the embryo has XY chromosomes, a gene on the Y chromosome called SRY will activate within a couple weeks of conception and begin to differentiate the embryo into one with male genitals.

However, it turns out that breast tissue begins to develop before SRY kicks in, and since nipples in men essentially do no harm, Gould and Lewontin argue, there has simply never been a good enough reason—evolutionarily speaking—to do away with them. They linger because they're benign. Or as Andrew M. Simons, a professor of biology at Carleton University in Ottawa, Ontario wrote in Scientific American, "The presence of nipples in male mammals is a genetic architectural by-product of nipples in females. So, why do men have nipples? Because females do."

5. THE WORLD'S STRONGEST NIPPLES BELONG TO THE GREAT NIPPULINI.

Who needs pecs when you have nipples like those of The Great Nippulini, a.k.a. Sage Werbock, a performer who makes a living demonstrating the mighty power of his nipples? Each nipple can lift 70 pounds, and he holds a Guinness record for the heaviest vehicle pulled by nipples for 20 meters (66 feet)—988.5 kilograms (2179.27 pounds). He has also lifted a variety of dumbbells, anvils, and bowling balls.

6. THEY'RE VERY SENSITIVE TO STIMULATION.

It's no secret that many people take sexual pleasure from nipple stimulation. However, Michael Reitano, an expert in sexual health and wellness at Roman Health in New York, brings up a study published in 2011 in which researchers set out to map the neurology of sexual stimulation in women. Through MRI imaging, they determined that "when [the nipple is] stimulated, the sensations travel to the same part of the brain that is stimulated when the clitoris, vagina, or cervix is stimulated," Reitano says. The study, published in the Journal of Sexual Medicine, also confirmed that it was possible for some women to have an orgasm by nipple stimulation alone.

While the same brain mapping has not yet been done on men, "there is every reason to believe that it has some capacity to function as a source of sexual pleasure for men as well," Reitano tells Mental Floss.

7. NIPPLES ARE AS UNIQUE AS FINGERPRINTS.

Nipples come in many colors, including pale pink, reddish-beige, brown, and black. Your own two nipples can even vary from each other, as can the areolae. "They also come in many different shapes," O'Connor says. "Some are more flat, while others can be quite bulbous. A person can have two nipples that look very different from each other. Asymmetry is normal."

8. A SPECIFIC KIND OF BREAST CANCER TARGETS THE NIPPLE.

While most forms of breast cancer affect the whole breast, Paget disease of the breast is a rare cancer that targets the skin and ducts of the nipple. "Most patients get a rash on the nipples that looks like a severe case of eczema. It is a cancer of breast epithelial (skin) cells," Chen says. Paget disease of the breast represents between 0.5 and 5 percent of all breast cancers.

9. AFTER MASTECTOMY, NIPPLE SENSATION CAN OCCASIONALLY BE RESTORED.

In breast cancer cases where mastectomy—removal of the breast—is necessary, it is sometimes possible to spare the nipple, allowing for a more realistic post-treatment reconstruction, though sensation is often lost. However, Chen says that in certain cases, "it is possible to restore sensation to the nipples with nerve repairs and nerve grafts when a woman undergoes natural tissue breast reconstruction. Sensory restoration to the nipple after mastectomy is very cutting edge, but if you find the right surgeon, it is possible."

10. NIPPLE STIMULATION CAN HELP INDUCE LABOR IN PREGNANT WOMEN.

When a woman is ready to give birth but the baby isn't, one piece of often-shared advice is to stimulate the mother's nipples to induce labor. A 2005 analysis of six trial studies found a significant decrease in the number of women who hadn't gone into labor after 72 hours. Just under 63 percent of the women who received stimulation were not in labor versus 94 percent who hadn't received it.

The mechanism isn't entirely clear, but breast stimulation causes the uterus to contract. It may also help release the hormone oxytocin, which can start contractions. Once the baby's born, the baby's suckling also has benefits for the mother. "When a newborn suckles, the increased oxytocin causes the uterus to contract [and shrink to its original size over the subsequent weeks] following birth," Reitano explains.

11. BREAST MILK HAS MULTIPLE WAYS TO EXIT THE NIPPLE.

If you've ever pumped your own breast milk or seen it done, you may have noticed that the milk doesn't just come out in a single stream. In a typical nipple, "There are between four and 20 outlets for the milk to come out—it can look like one stream or [coming from] various holes," O'Connor says.

nextArticle.image_alt|e
iStock
arrow
The Body
12 Fantastic Facts About the Immune System
iStock
iStock

If it weren't for our immune system, none of us would live very long. Not only does the immune system protect us from external pathogens like viruses, bacteria, and parasites, it also battles cells that have mutated due to illnesses, like cancer, within the body.

Here are 12 fighting facts about the immune system.

1. THE IMMUNE SYSTEM SAVES LIVES.

The immune system is a complex network of tissues and organs that spreads throughout the entire body. In a nutshell, it works like this: A series of "sensors" within the system detects an intruding pathogen, like bacteria or a virus. Then the sensors signal other parts of the system to kill the pathogen and eliminate the infection.

"The immune system is being bombarded by all sorts of microbes all the time," Russell Vance, professor of immunology at University of California, Berkeley and an investigator for the Howard Hughes Medical Institute, tells Mental Floss. "Yet, even though we're not aware of it, it's saving our lives every day, and doing a remarkably good job of it."

2. BEFORE SCIENTISTS UNDERSTOOD THE IMMUNE SYSTEM, ILLNESS WAS CHALKED UP TO UNBALANCED HUMORS.

Long before physicians realized how invisible pathogens interacted with the body's system for fighting them off, doctors diagnosed all ills of the body and the mind according to the balance of "four humors": melancholic, phlegmatic, choleric, or sanguine. These criteria, devised by the Greek philosopher Hippocrates, were divided between the four elements, which were linked to bodily fluids (a.k.a. humors): earth (black bile), air (blood), water (phlegm) and fire (yellow bile), which also carried properties of cold, hot, moist, or dry. Through a combination of guesswork and observation, physicians would diagnose patients' humors and prescribe treatment that most likely did little to support the immune system's ability to resist infection.

3. TWO MEN WHO UNRAVELED THE IMMUNE SYSTEM'S FUNCTIONS WERE BITTER RIVALS.

Two scientists who discovered key functions of the immune system, Louis Pasteur and Robert Koch, should have been able to see their work as complementary, but they wound up rivals. Pasteur, a French microbiologist, was famous for his experiments demonstrating the mechanism of vaccines using weakened versions of the microbes. Koch, a German physician, established four essential conditions under which pathogenic bacteria can infect hosts, and used them to identify the Mycobacterium tuberculosis bacterium that causes tuberculosis. Though both helped establish the germ theory of disease—one of the foundations of modern medicine today—Pasteur and Koch's feud may have been aggravated by nationalism, a language barrier, criticisms of each other's work, and possibly a hint of jealousy.

4. SPECIALIZED BLOOD CELLS ARE YOUR IMMUNE SYSTEM'S GREATEST WEAPON.

The most powerful weapons in your immune system's arsenal are white blood cells, divided into two main types: lymphocytes, which create antigens for specific pathogens and kill them or escort them out of the body; and phagocytes, which ingest harmful bacteria. White blood cells not only attack foreign pathogens, but recognize these interlopers the next time they meet them and respond more quickly. Many of these immune cells are produced in your bone marrow but also in the spleen, lymph nodes, and thymus, and are stored in some of these tissues and other areas of the body. In the lymph nodes, which are located throughout your body but most noticeably in your armpits, throat, and groin, lymphatic fluid containing white blood cells flows through vein-like tubules to escort foreign invaders out.

5. THE SPLEEN HELPS YOUR IMMUNE SYSTEM WORK.

Though you can live without the spleen, an organ that lies between stomach and diaphragm, it's better to hang onto it for your immune function. According to Adriana Medina, a doctor who specializes in hematology and oncology at the Alvin and Lois Lapidus Cancer Institute at Sinai Hospital in Baltimore, your spleen is "one big lymph node" that makes new white blood cells, and cleans out old blood cells from the body.

It's also a place where immune cells congregate. "Because the immune cells are spread out through the body," Vance says, "eventually they need to communicate with each other." They do so in both the spleen and lymph nodes.

6. YOU HAVE IMMUNE CELLS IN ALL OF YOUR TISSUES.

While immune cells may congregate more in lymph nodes than elsewhere, "every tissue in your body has immune cells stationed in it or circulating through it, constantly roving for signs of attack," Vance explains. These cells also circulate through the blood. The reason for their widespread presence is that there are thousands of different pathogens that might infect us, from bacteria to viruses to parasites. "To eliminate each of those different kinds of threats requires specialized detectors," he says.

7. HOW FRIENDLY YOU'RE FEELING COULD BE LINKED TO YOUR IMMUNE SYSTEM.

From an evolutionary perspective, humans' high sociability may have less to do with our bigger brains, and more to do with our immune system's exposure to a greater number of bacteria and other pathogens.

Researchers at the University of Virginia School of Medicine have theorized that interferon gamma (IG), the immune cytokine that helps the immune system fight invaders, was linked to social behavior, which is one of the ways we become exposed to pathogens.

In mice, they found IG acted as a kind of brake to the brain's prefrontal cortex, essentially stopping aberrant hyperactivity that can cause negative changes in social behavior. When they blocked the IG molecule, the mice's prefrontal cortexes became hyperactive, resulting in less sociability. When they restored the function, the mice's brains returned to normal, as did their social behavior.

8. YOUR IMMUNE SYSTEM MIGHT RECRUIT UNLIKELY ORGANS—LIKE THE APPENDIX—INTO ITS SERVICE.

The appendix gets a bad rap as a vestigial organ that does nothing but occasionally go septic and create a need for immediate surgery. But the appendix may help keep your gut in good shape. According to Gabrielle Belz, professor of molecular immunology at the Walter and Eliza Hall Institute of Medical Research in Melbourne, Australia, research by Duke University's Randal Bollinger and Bill Parker suggests the appendix houses symbiotic bacteria that are important for overall gut health—especially after infections wipe out the gut's good microbes. Special immune cells known as innate lymphoid cells (ILCs) in the appendix may help to repopulate the gut with healthy bacteria and put the gut back on track to recovery.

9. GUT BACTERIA HAS BEEN SHOWN TO BOOST IMMUNE SYSTEMS IN MICE.

Researchers at the University of Chicago noticed that one group of mice in their lab had a stronger response to a cancer treatment than other mice. They eventually traced the reason to a strain of bacteria—Bifidobacterium—in the mice's guts that boosted the animals' immune system to such a degree they could compare it to anti-cancer drugs called checkpoint inhibitors, which keep the immune system from overreacting.

To test their theory, they transferred fecal matter from the robust mice to the stomachs of less immune-strengthened mice, with positive results: The treated mice mounted stronger immune responses and tumor growth slowed. When they compared the bacterial transfer effects with the effects of a checkpoint inhibitor drug, they found that the bacteria treatment was just as effective. The researchers believe that, with further study, the same effect could be seen in human cancer patients.

10. SCIENTISTS ARE TRYING TO HARNESS THE IMMUNE SYSTEM'S "PAC-MAN" CELLS TO TREAT CANCER.

Aggressive pediatric tumors are difficult to treat due to the toxicity of chemotherapy, but some researchers are hoping to develop effective treatments without the harmful side effects. Stanford researchers designed a study around a recently discovered molecule known as CD47, a protein expressed on the surface of all cells, and how it interacts with macrophages, white blood cells that kill abnormal cells. "Think of the macrophages as the Pac-Man of the immune system," Samuel Cheshier, lead study author and assistant professor of neurosurgery at Stanford Medicine, tells Mental Floss.

CD47 sends the immune system's macrophages a "don't eat me" signal. Cancer cells fool the immune system into not destroying them by secreting high amounts of CD47. When Cheshier and his team blocked the CD47 signals on cancer cells, the macrophages could identify the cancer cells and eat them, without toxic side effects to healthy cells. The treatment successfully shrank all five of the common pediatric tumors, without the nasty side effects of chemotherapy.

11. A NEW THERAPY FOR TYPE 1 DIABETES TRICKS THE IMMUNE SYSTEM.

In those with type 1 diabetes, the body attacks its own pancreatic cells, interrupting its normal ability to produce insulin in response to glucose. In a 2016 paper, researchers at MIT, in collaboration with Boston's Children's Hospital, successfully designed a new material that allows them to encapsulate and transplant healthy pancreatic "islet" cells into diabetic mice without triggering an immune response. Made from seaweed, the substance is benign enough that the body doesn't react to it, and porous enough to allow the islet cells to be placed in the abdomen of mice, where they restore the pancreatic function. Senior author Daniel Anderson, an associate professor at MIT, said in a statement that this approach "has the potential to provide [human] diabetics with a new pancreas that is protected from the immune system, which would allow them to control their blood sugar without taking drugs. That's the dream."

12. IMMUNOTHERAPY IS ON THE CUTTING EDGE OF IMMUNE SYSTEM RESEARCH.

Over the last few years, research in the field of immunology has focused on developing cancer treatments using immunotherapy. This method engineers the patient's own normal cells to attack the cancer cells. Vance says the technique could be used for many more conditions. "I feel like that could be just the tip of the iceberg," he says. "If we can understand better what the cancer and immunotherapy is showing, maybe we can go in there and manipulate the immune responses and get good outcomes for other diseases, too."

SECTIONS

arrow
LIVE SMARTER