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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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The Prehistoric Bacteria That Helped Create Our Cells Billions of Years Ago
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We owe the existence of our cells—the very building blocks of life—to a chance relationship between bacteria that occurred more than 2 billion years ago. Flash back to Bio 101, and you might remember that humans, plants, and animals have complex eukaryotic cells, with nucleus-bound DNA, instead of single-celled prokaryotic cells. These contain specialized organelles such as the mitochondria—the cell’s powerhouse—and the chloroplast, which converts sunlight into sugar in plants.

Mitochondria and chloroplasts both look and behave a lot like bacteria, and they also share similar genes. This isn’t a coincidence: Scientists believe these specialized cell subunits are descendants of free-living prehistoric bacteria that somehow merged together to form one. Over time, they became part of our basic biological units—and you can learn how by watching PBS Eons’s latest video below.

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11 Primal Facts About Dian Fossey
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Born in San Francisco on January 16, 1932, Dian Fossey came from a world far removed from the dense jungles of East Africa. She discovered that environment in her thirties and spent the final decades of her life studying the gorillas that lived there. From her groundbreaking primatology work to her mysterious death, here are 11 facts about the scientist behind Gorillas in the Mist.

1. HER LOVE OF ANIMALS BEGAN WITH A PET GOLDFISH.

Though she went on to become one of history's most famous animal-lovers, Fossey didn't grow up in a pet-friendly household. The only animal she was allowed to keep as a child was a single goldfish. She loved her fish, but when it died, her parents barred her from getting another animal to replace it. Even a pet hamster offered to her by a classmate was forbidden from entering the house.

2. SHE WAS A PRIZE-WINNING EQUESTRIAN.

Not permitted to keep pets in the home, Fossey nurtured her passion for animals through equestrianism. She received her first horseback-riding lesson at age 6. By the time she reached her teen years, she was advanced enough to merit an invitation to join the riding team at Lowell High School in San Francisco. Her hobby earned her several awards and pushed her to pursue an education in animal husbandry at the University of California, Davis. Even after she'd shifted career aspirations to occupational therapy, Fossey chose to move to Kentucky to be closer to farm life.

3. SHE SPENT HER LIFE SAVINGS ON HER FIRST TRIP TO AFRICA.

Dian Fossey was 31 when she first stepped foot on the continent where she'd complete her most important work. Inspired by a friend's trip to Africa, she collected her life savings (about $8000), took out a three-year bank loan, and planned a seven-week trip through the wilderness of Kenya, Tanzania, Congo, and Zimbabwe. On her adventures there she met Louis Leakey, the anthropologist famous for sponsoring the all-woman trio of primatology pioneers (the "trimates") that included Jane Goodall, Biruté Galdikas, and eventually Dian Fossey herself. It was also during this period when Fossey saw gorillas in the wild for the first time. She met wildlife photographers Joan and Alan Root and joined them on an expedition to photograph the animals in the Congolese mountains. The vacation wasn't scientific in nature, but as Fossey later wrote, "The seed was planted in my head, even if unconsciously, that I would someday return to Africa to study the gorillas of the mountains."

4. SHE PROVED HER DEDICATION WITH AN APPENDECTOMY.

Leakey reconnected with Fossey back in the States in 1966. The anthropologist had spent the last several years supporting his former secretary Jane Goodall in her chimpanzee research, and now he was in search of a candidate to do for gorillas what Goodall had done for chimps. After getting to know Fossey better, he decided she was the right woman for the job. He offered to gather the funding for her trip back to Africa, but before she left she would need to remove her appendix as a precaution. This didn't scare her off. When Leakey wrote six weeks later to say the surgery wouldn't be necessary and he had just wanted to make sure she was committed, she was already appendix-less.

5. HER FIRST RESEARCH EXPEDITION ENDED ABRUPTLY.

Fossey returned to the Congo toward the end of 1966—just months before a civil war erupted in the already volatile region. Rebel soldiers captured her at her base camp in July 1967. After spending two weeks in military detainment, she was able to bribe her way out with promises of cash and her Land Rover. The guards agreed to drive her to Uganda, and shortly after they arrived, she had them arrested. After the scare, Fossey was ready to resume her research almost immediately: This time she set up camp in Rwanda, ignoring warnings from the U.S. Embassy.

6. SHE UNCOVERED THE GORILLAS' TRUE NATURE.

Prior to Fossey's research, the public viewed gorillas as beasts similar in temperament to King Kong. She quickly disproved the notion that gorillas were bloodthirsty animals that would attack humans when given the chance.

To infiltrate their society, she adopted their habits. Walking on her knuckles and chewing on celery stalks allowed her to gain the apes' trust. As long as she maintained a nonthreatening profile and made her presence known at all times, she was safe around the gentle behemoths. Today we know that despite their intimidating size, gorillas are some of the least violent members of the great ape family.

7. SHE EARNED A UNIQUE NICKNAME FROM LOCALS.

Dian Fossey spent enough time at her research center in Rwanda to garner a reputation. To the locals she was Nyiramachabelli, a Swahili name that when roughly translated means "the woman who lives alone on the mountain."

8. SHE USED THE GORILLAS' NOSES TO TELL THEM APART.

Many of the gorillas Fossey studied were given names, such as Peanut, Rafiki, and Uncle Bert. Fossey used another method to tell her subjects apart: She drew sketches of their noses. Each gorilla has a unique pattern of wrinkles around its nose that makes it easy to identify. These nose prints are the equivalent of fingerprints in humans, but instead of getting up close to study them, Fossey was able to document them from far away using binoculars and a sketchpad.

9. ONE OF HER GORILLAS IS ALIVE TODAY.

Hundreds of gorillas made it into Dian Fossey's body of research. In 2017, only one specimen from that original pool is still alive. Poppy was born into a group of gorillas on Fossey's radar in 1976. The researcher documented the animal's birth and childhood in her journals. Today, at 41, Poppy is the oldest gorilla currently monitored by the Dian Fossey Fund.

10. HER WORK IS THE SUBJECT OF A BOOK, A MOVIE, AND AN OPERA.

In 1983, Fossey published the book that helped make her famous. Gorillas in the Mist is the autobiographical account of her first 13 years in the African jungle and the scientific discoveries she made about the gorillas living there. The title went on to become a bestseller. Five years later, Sigourney Weaver starred as Fossey in a film of the same name. The biopic snagged five Oscar nominations and converted Weaver into a gorilla conservationist.

There's another dramatization of Fossey's life that's not so widely known: In 2006, the Kentucky Opera VISIONS! program staged an opera called Nyiramachabelli—a nod to the researcher's nickname.

11. HER DEATH REMAINS A MYSTERY.

Next to her groundbreaking gorilla research, Fossey is perhaps best known for her mysterious and tragic murder. On December 27, 1985, she was found dead in her cabin at her Rwandan research camp. The cause of death was a machete blow to the head, but the identity of her assailant remains unknown to this day. (A Rwandan court convicted in absentia her American research assistant, Wayne McGuire, for her murder and sentenced him to death. McGuire, who fled Rwanda before the conviction, has always maintained his innocence.) Fossey was buried in the nearby mountains beside the grave of her favorite gorilla Digit, who had been slaughtered by poachers years earlier. Before she was killed, Fossey wrote one final entry in her diary. It reads:

“When you realize the value of all life, you dwell less on what is past and concentrate on the preservation of the future.”

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