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7 Sanguine Facts About Human Blood

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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. That’s why we’re launching a new series called The Body, which will explore human anatomy, part by part. Think of it as a mini digital encyclopedia with a dose of wow.
 

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. FROM HIPPOCRATES' HUMORS TO BLOODLETTING AND LEECHES

Long before we had scientific proof of the importance of the circulation system, ancient people knew it was important to 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, for example, 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. That said, it hasn’t completely disappeared. Bloodletting has actually been proven an effective treatment for some rare conditions like hemochromatosis, an excess of iron in the body that can lead to liver disease and heart problems.

Today 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. This 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, skin grafting, and reattaching fingers and toes. (By the way, it turns out that even the blood-sucking variety of leech is not all that interested in human blood, contrary to popular belief.)

2. SCIENTISTS DIDN'T DISCOVER HOW BLOOD CIRCULATION ACTUALLY WORKED TILL 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 ONLY DISCOVERED IN THE EARLY 20TH CENTURY.

Austrian physician Karl Landsteiner first 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. Got it?

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 (5.30 quarts) of blood (except pregnant women, whose bodies can produce about 50 percent more blood in order to nourish their fetus.)

Plasma, the liquid portion of our 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 are joined by electrolytes, antibodies, vitamins, proteins, and other nutrients required to nourish all the other cells in the body.

5. THE LIFE SPAN OF A HEALTHY RED BLOOD CELL IS ONLY ABOUT 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 our bone marrow. But not everyone produces the healthy ones. Sufferers of sickle cell anemia, a hereditary condition, develop malformed red blood cells that can’t move easily through blood vessels. These blood cells last only 10 to 20 days, which leads to a chronic shortage of red blood cells, often causing to pain, infection, and organ damage.

6. BLOOD COULD POTENTIALLY PLAY A ROLE IN TREATING ALZHEIMER'S.

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, as well as muscle stem cells.

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. The scientist who led the research is now testing the effects of young plasma on Alzheimer’s patients.

And in August, a California start-up announced it would conduct a clinical trial with volunteers 35 and older to see if a young (human) plasma injection offered anti-aging benefits. That trial is proving controversial, however, because of the price tag: The company will charge patients $8000 to participate.

7. AFRAID OF BLOOD? THERE'S A DIAGNOSIS FOR THAT.

If you’ve cringed your way through this list, you’re not alone—many are a bit squeamish about blood. But 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. It’s 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. This is 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 BII sufferers, this so-called 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.

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11 Facts About Fingernails
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Whether there's dirt beneath them or polish atop them, your fingernails serve more than just decorative purposes: They help keep your fingertips safe and have a multitude of special functions that even your doctor might not be aware of. “The nails occupy a unique space within dermatology and medicine in general, particularly because they are such a niche area about which few people have expertise,” Evan Rieder, assistant professor in the Ronald O. Perelman Department of Dermatology at NYU Langone Health, tells Mental Floss.

1. FINGERNAILS HAVE FOUR MAIN PARTS.

Along with skin and hair, nails are part of the body's integumentary system, whose main function is to protect your body from damage and infection. Fingernails have four basic structures: the matrix, the nail plate, the nail bed, and the skin around the nail (including the cuticle).

Fingernail cells grow continuously from a little pocket at the root of the nail bed called the matrix. The pale, crescent-shaped lunula—derived from Latin for "little moon"—on the nail itself is the visible portion of the matrix. If the lunula is injured, the  nail won't grow normally (a scarred lunula can result in a split nail), and changes in the lunula's appearance can also be signs of a systemic disease.

Fingernail cells are made of a protein called keratin (same as your hair). As the keratin cells push out of the matrix, they become hard, flat and compact, eventually forming the hard surface of the nail known as the nail plate. Beneath that is the nail bed, which almost never sees the light of day except when there's an injury or disease.

Surrounding the matrix is the cuticle, the semi-circle of skin that has a tendency to peel away from the nail. The skin just underneath the distal end of the fingernail is called the hyponychium, and if you've ever trimmed your nails too short, you know this skin can be slightly more sensitive than the rest of the fingertip.

2. THEY GROW AT A RATE OF 0.1 MILLIMETERS A DAY ...

That's about 3 to 4 millimeters per month. But they don't always grow at the same speed: Fingernails grow more quickly during the day and in summer (this may be related to exposure to sunlight, which produces more nail-nourishing vitamin D). Nails on your bigger fingers also grow faster, and men's grow faster than women's. The pinky fingernail grows the slowest of all the fingernails. According to the American Academy of Dermatology, if you lose a fingernail due to injury, it can take up to six months to grow back (while a toenail could take as much as a year and a half).

3. ... BUT NOT AFTER YOU'RE DEAD.

You've probably heard that your fingernails keep growing after death. The truth is, they don't, according to the medical journal BMJ. What's actually happening is that the skin around the base of the fingernails retracts because the body is no longer pumping fluids into the tissues, and that creates a kind of optical illusion that makes the nails appear longer.

4. ITS ESTIMATED THAT 20 TO 30 PERCENT OF PEOPLE BITE THEIR NAILS.

Scientists say it's still unclear why, but they suspect nail-biters do it because they're bored, frustrated, concentrating, or because it just feels comforting (and anxiety doesn't seem to play a big role). Perfectionists who don't like to be idle are very likely to have the habit. Biters expose themselves to the dangerous crud that collects underneath the nail: The hyponychium attracts bacteria, including E. coli, and ingesting that through nail-biting can lead to gastrointestinal problems down the line. Biting can also damage teeth and jaws.

5. HUMAN FINGERNAILS ARE BASICALLY FLAT CLAWS.

Our primate ancestors had claws—which, like nails, are made of keratin. As human ancestors began using tools some 2.5 million years ago (or even earlier), evolutionary researchers believe that curved claws became a nuisance. To clutch and strike stone tools, our fingertips may have broadened, causing the claws to evolve into fingernails.

6. THE NAIL ACTUALLY MAKES YOUR FINGERTIP MORE SENSITIVE.

While the fingernail may be tough enough to protect tender flesh, it also has the paradoxical effect of increasing the sensitivity of the finger. It acts as a counterforce when the fingertip touches an object. "The finger is a particularly sensitive area because of very high density of nerve fibers," Rieder says.

7. FINGERNAILS CAN REVEAL LUNG, HEART, AND LIVER DISEASES.

"One of the most interesting facts about fingernails is that they are often a marker for disease within the body," Rieder says. Nail clubbing—an overcurvature of the nail plate and thickening of the skin around the nails—is a particularly significant sign of underlying illness, such as lung or heart disease, liver disease, or inflammatory bowel disease. Two-toned nails—whitish from the cuticle to the nail's midpoint and pink, brown, or reddish in the distal half—can be a sign of kidney and liver disease. Nails that are two-thirds whitish to one-third normal can also be a sign of liver disease. However, little white marks on your nails, known as milk spots (or punctate leukonychia) are just the remnants of any kind of trauma to the nail, from slamming it in a door to chewing on it too fervently.

8. YOU CAN GET A COMMON SKIN DISEASE ON YOUR NAILS.

Psoriasis is "typically thought of as a skin disease, but is actually a skin, joint, and nail disease, and when severe, a marker of cardiovascular risk," Rieder says. Psoriatic fingernails may have orange patches called oil spots, red lines known as splinter hemorrhages, lifting of the edges of the nails, and pits, "which look like a thumb tack was repeatedly and haphazardly pushed into the nails," he says.

Doctors often prescribe topical or injected corticosteroids to treat psoriatic nails, but using lasers is an emerging and potentially more cost-effective technique. Rieder relies on a pulsed dye laser, which uses an organic dye mixed with a solvent as the medium to treat nail psoriasis, "which can be both medically and aesthetically bothersome," he says. This laser is able to penetrate through the hard nail plate with minimal discomfort and "to treat targets of interest, in the case of psoriasis, blood vessels, and hyperactive skin," Rieder says.

9. ANCIENT CULTURES DISPLAYED SOCIAL STATUS WITH NAIL ART.

Painting and other forms of decorating nails have a history of offering social and aesthetic cues through variations in nail color, shape, and length, Rieder says. In fact, he adds, in some cultures ornate and well-decorated fingernails "serve as a proxy for social status."

Five thousand years ago in China, men and women of the Ming Dynasty aristocracy grew their nails long and covered them with golden nail guards or bright home-made polishes. The long nails allegedly announced to the world their social rank and their freedom from performing menial labor.

10. A FORMER BEAUTICIAN HELD THE WORLD RECORD FOR THE LONGEST NAILS.

Lee Redmond of Utah started growing her nails in 1979 and kept at it until she held the world record for "longest fingernails on a pair of hands ever (female)" in 2008. Her right thumbnail was 2 feet, 11 inches and the collective length of all her nails was 28 feet, 4 inches. She also applied nail hardener daily and painted them a reflective gold. Unfortunately, she broke her nails in a 2009 car accident and has no plans to regrow them.

More recently, the man who holds the Guinness record for the "longest fingernails on a single hand—ever" chose to chop them off at Ripley's Believe It Or Not! in New York City in July 2018. Shridhar Chillal of Pune, India started growing the nails of his left hand in 1952, when he was 14 years old. At last count, the total length measured 29 feet, 10.1 inches.

11. THE FIRST NAIL CLIPPERS WERE PATENTED IN 1875.

Today, biters don't have to use their teeth to trim their nails. While the earliest tools for cutting nails were most likely sharp rocks, sand, and knives, the purpose-built nail clipper—though it might be more accurately called a circular nail file—was designed by a Boston, Massachusetts inventor named Valentine Fogerty and patented in 1875. The nail clippers we know today were the design of inventors Eugene Heim and Oelestin Matz, who were granted their patent for a clamp-style fingernail clipper in 1881.

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Billion-Year-Old Rocks Reveal the First Color Ever Produced by a Living Thing
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Billions of years ago, before there were plants and animals on Earth, there were rocks, tiny organisms, water, and not much else. It’s hard to envision what our barren planet looked like back then, but scientists now have some idea of what colors dominated the landscape.

As Vice reports, a team of researchers from Australian National University (ANU) were able to pinpoint the oldest colors ever produced by a living creature: purple-red hues dating back more than 1.1 billion years. The pigments, which appear pink when diluted, were found in molecular fossils of chlorophyll that had been preserved in rocks beneath the Sahara desert. A billion years ago, though, this area was “an ancient ocean that has long since vanished,” Nur Gueneli of ANU said in a statement.

Chlorophyll may very well be green, but these pinkish pigments are a result of "fossilized porphyrins, a type of organic compound that forms an atomic ring around a magnesium ion to form a chlorophyll molecule," Vice explains.

While this provides an interesting visual, the color itself is less important than what it reveals about some of the earliest life forms on Earth. Scientists determined that the chlorophyll was produced by ancient organisms called cyanobacteria, which derived energy via photosynthesis and ruled the oceans at that time, researchers wrote in a paper published in the Proceedings of the National Academy of Sciences. Larger planktonic algae—a potential food source for bigger life forms— were scarce, which may explain why large organisms didn’t roam the Earth a billion years ago. That kind of algae was about a thousand times larger than the cyanobacteria.

“The cyanobacterial oceans started to vanish about 650 million years ago, when algae began to rapidly spread to provide the burst of energy needed for the evolution of complex ecosystems, where large animals, including humans, could thrive on Earth," ANU associate professor Jochen Brocks said.

So the next time you encounter algae, you can thank it for helping you secure a spot on this planet.

[h/t Vice]

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