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The Uterus: A Natural History

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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.
 

At only 3 inches long and weighing about 60 grams, the uterus isn’t a flashy, attention-grabbing organ. When it comes to human health, the heart usually comes first, followed by the brain, then perhaps the digestive system. Yet the uterus plays an outsized role. It’s the carrier of all life, the subject of scrutiny in political forums, and a source of delight and despair for sexually mature women. It causes bleeding and pain, allows 211 million women to get pregnant every year, and is partially responsible for the 10 to 20 percent of those pregnancies that end in miscarriage.

Despite its ability to create life, there are dozens of crucial things we have yet to learn about the uterus. At least we’ve abandoned the theory that it travels freely around the body, causing hysteria, and that it can be manipulated by smelling salts.

Today we know the uterus sits low in the abdomen, held in place by muscles and ligaments. It is connected to the vagina by the cervix and receives unfertilized eggs from the ovaries via the fallopian tubes, which are connected to both sides of the uterus. It expands from 3 inches to the size of a watermelon by the end of a pregnancy in order to hold the baby and placenta—and, luckily for new mothers, naturally deflates about six weeks after the child is born.

But how did we develop this organ, how does it operate—or malfunction—in the body, and what's the outlook for the future?

THE EXTRAORDINARY EVOLUTION OF THE MAMMALIAN UTERUS

Until recently, scientists didn’t even understand how mammals evolved uteruses that allowed for live birth. Soft tissue is rarely preserved in the fossil record, which means scientists can study the bone structure of past organisms but are often left guessing when it comes to organs.

Up until marsupial ancestors appeared 220 million years ago, new life came out of eggs. Before that time, even the earliest mammalian predecessors, the group called monotremes (like echidnas and platypuses) were still laying eggs. But by 105 million years ago, placental mammals had evolved elaborate uteruses that allowed for invasive placentas, maternal tolerance of the fetus, and long gestation periods. What caused this evolution? Why did mammals suddenly appear?

In 2015, a team of researchers from the University of Chicago, Yale, and several other universities found a major clue in the hunt to discover the origin of mammals: genetic parasites. Called transposons, these snippets of non-protein-coding DNA regularly changed positions in the genome, an action called “jumping genes.” The leap-frogging transposons caused genes from other tissues—like the brain and digestive system—to be activated in the uterus. As more and more genes were expressed in the uterus, organisms shifted from producing eggs to giving live birth. The shift began sometime between 325 and 220 million years ago with the appearance of monotremes, and continued for hundreds of millions of years until placental mammals appeared, sometime between 176 and 105 million years ago.

During the genetic shift, more than 1000 genes turned on in therians, common ancestors to marsupials and placental mammals (like us). Many of these genes related to maternal-fetal communication, and especially the suppression of the maternal immune system in the uterus so it didn't reject the developing fetus. Because many of the transposons had progesterone binding sites that regulated the process, the uterus evolved to be extremely sensitive to that hormone (which is produced by the ovaries during the release of a mature egg; it prepares the uterine lining to receive a fertilized egg). The study appeared in the journal Cell Reports. In a press statement, Vincent Lynch, one of the study’s authors, said the discovery shed light on how “something completely novel evolves in nature.”

“It’s easy to imagine how evolution can modify an existing thing, but how new things like pregnancy evolve has been much harder to understand,” Lynch continued. “We now have a new mechanistic explanation of this process that we’ve never had before.”

THE MYSTERIES OF MENSTRUATION

While live birth defines mammals, including everything from whales to dogs to bats, there’s one thing that sets humans apart from most other species: menstruation. We’re part of an exclusive club that’s limited to old world primates, elephant shrews, and fruit bats. All other species remodel and reabsorb the endometrium, or uterine lining. So why do humans have to deal with the hassle of a period? Scientists aren’t quite sure. One theory is that the process protects us from abnormal pregnancies. The human gestation period is so long and requires so many biological resources that it’s better to reject all but the best candidates. And the reason we have periods is far from the only thing we don’t understand about menstruation.

“There is so much we don’t know,” says Hilary Critchley, OB/GYN and professor of reproductive sciences at the University of Edinburgh. “Not only why do we have normal periods, but particularly why does a woman have heavier periods?” Critchley and her colleagues published a paper that compiled years’ worth of studies in Human Reproduction Update in July 2015. They found far more questions than answers. Their research confirmed what is known: that a decline in progesterone triggers menstruation, and that the endometrial coagulation system plays a part in stopping the bleeding. But plenty of questions remain about the mechanics of the process.

Doctors don’t know what regulates inflammation during menstruation, what causes the bleeding to stop, or how the uterus repairs itself so quickly without creating any scar tissue. They also don’t understand the causes of diseases associated with menstruation, like polycystic ovary syndrome and endometriosis. Neither currently has a cure, and they afflict around 1 in 10 women. In the most extreme cases of endometriosis, women have no choice but to undergo hysterectomies.

“If you’re in the workforce, period problems can be really embarrassing and really difficult to deal with. This is where I see the unmet need for new treatments,” Critchley tells mental_floss. “A woman now has 400 periods in a lifetime. A woman (100 years ago) had 40. If you’ve got more periods, you’ve got more opportunity for it to be a problem.” This increase in the number of periods by a factor of 10 in the past 100 years is due to contraception and improved nutrition. The downside is that's a lot more opportunity for menstruation to cause problems.

GROWING AN EXTRA ORGAN TO MAKE A BABY

Menstruation isn’t the only area of female reproductive health that has researchers scratching their heads. Perhaps even more confounding is the placenta, a transient organ created during pregnancy by the embryo.

“I’d say the placenta is probably the least studied and the least understood organ in the body,” says Catherine Spong, acting director of the National Institute of Child and Human Development. She oversees the Human Placenta Project (HPP), which aims to develop new tools to monitor the placenta throughout its development. “If you could understand how the placenta allows two genetically distinct entities not only to grow, but also thrive, the implications for enhancing our understanding of immunology and transplant medicine would be pretty remarkable.”

Stacy Zamudio, a recipient of a grant from the HPP and director of research at Hackensack University Medical Center, calls the placenta “the most wonderful organ ever.” Her research focuses on placenta accreta (when the placenta grows too deeply into the mother’s uterine wall and even outside organs).

“It breathes, it produces hormones, it produces immunologic factors that protect the baby against infection. It acts like a skin, a liver, a kidney, a lung—it does all the functions of the other organs in one organ,” Zamudio says.

Human Placenta Project

The placenta achieves this by hooking into arteries in the uterus, essentially hijacking the mother’s body so the embryo can have a constant stream of nutrients and oxygen as it develops. When it’s functioning normally, the placenta ensures a positive outcome: healthy baby, healthy mother. But when things go wrong with the placenta, they quickly go from bad to worse.

The placenta can be under-invasive, meaning the connection to the mother’s blood isn’t strong enough. The baby stops developing because it’s not getting nutrients, and in the worst cases the mother can suffer from preeclampsia, which causes life-threateningly high blood pressure and can only be treated by immediate delivery of the baby. Or, as with the cases Zamudio studies, the placenta can be over-invasive, infiltrating the uterus and other organs beyond it like a cancer. Finally, in a complication known as placental abruption, the placenta can peel away from the uterus before delivery, removing the baby’s source of oxygen and nutrients and causing heavy bleeding in the mother.

Pregnancy can be a dangerous balancing act, and if doctors had better ways of monitoring the placenta’s development over the course of pregnancy, they might be able to prevent or avert the worst outcomes.

FROM WOMB TRANSPLANTS TO TRICORDERS

In October 2014, a baby born to a Swedish couple became an exciting example of the possible future of maternity—he was the first child ever born of a transplanted uterus. (The first pregnancy from a womb transplant, in Turkey, was terminated in 2013 when the fetus had no heartbeat.) The 36-year-old mother, who was herself born without a uterus, received a donation from a woman in her 60s, and had a frozen embryo successfully implanted in the transplanted organ. Although the child was born prematurely, he and the mother were otherwise healthy after the pregnancy. Since then, four more women who received uterus transplants from doctors at the University of Gothenburg have gotten pregnant. 

The pioneering surgery is now spreading across the world. Doctors at Cleveland Clinic performed the first successful uterus transplant in the U.S. just last week. The 9-hour surgery was performed on a 26-year-old patient with uterine factor infertility (an irreversible condition affecting 3 to 5 percent of women that prevents pregnancy). If the patient heals and can become pregnant, the surgery could offer new hope to women who previously thought they were doomed to infertility.

Despite the enormous advances made in the last decades concerning women's health, many questions about the uterus remain unanswered. Scientists don’t know why the placenta sometimes grows too little or too much, or how it communicates with the rest of the organs in the mother’s body. They don’t know why some women have debilitating cramps during their periods that have been likened to the pain of having a heart attack. But with scientists around the globe investing time and resources into such questions, it might not be long before we have real answers and solutions to these problems.

"We're not that far away from the tricorder in Star Trek," Zamudio says, referring to developing technologies like nanomagnetics. "I'm hoping that I'll be alive long enough to see a doctor be able to wave the instrument over the woman's abdomen and tell me what the glucose level is in that body."

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The Elements
9 Essential Facts About Carbon
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How well do you know the periodic table? Our series The Elements explores the fundamental building blocks of the observable universe—and their relevance to your life—one by one.
 
 
It can be glittering and hard. It can be soft and flaky. It can look like a soccer ball. Carbon is the backbone of every living thing—and yet it just might cause the end of life on Earth as we know it. How can a lump of coal and a shining diamond be composed of the same material? Here are eight things you probably didn't know about carbon.

1. IT'S THE "DUCT TAPE OF LIFE."

It's in every living thing, and in quite a few dead ones. "Water may be the solvent of the universe," writes Natalie Angier in her classic introduction to science, The Canon, "but carbon is the duct tape of life." Not only is carbon duct tape, it's one hell of a duct tape. It binds atoms to one another, forming humans, animals, plants and rocks. If we play around with it, we can coax it into plastics, paints, and all kinds of chemicals.

2. IT'S ONE OF THE MOST ABUNDANT ELEMENTS IN THE UNIVERSE.

It sits right at the top of the periodic table, wedged in between boron and nitrogen. Atomic number 6, chemical sign C. Six protons, six neutrons, six electrons. It is the fourth most abundant element in the universe after hydrogen, helium, and oxygen, and 15th in the Earth's crust. While its older cousins hydrogen and helium are believed to have been formed during the tumult of the Big Bang, carbon is thought to stem from a buildup of alpha particles in supernova explosions, a process called supernova nucleosynthesis.

3. IT'S NAMED AFTER COAL.

While humans have known carbon as coal and—after burning—soot for thousands of years, it was Antoine Lavoisier who, in 1772, showed that it was in fact a unique chemical entity. Lavoisier used an instrument that focused the Sun's rays using lenses which had a diameter of about four feet. He used the apparatus, called a solar furnace, to burn a diamond in a glass jar. By analyzing the residue found in the jar, he was able to show that diamond was comprised solely of carbon. Lavoisier first listed it as an element in his textbook Traité Élémentaire de Chimie, published in 1789. The name carbon derives from the French charbon, or coal.

4. IT LOVES TO BOND.

It can form four bonds, which it does with many other elements, creating hundreds of thousands of compounds, some of which we use daily. (Plastics! Drugs! Gasoline!) More importantly, those bonds are both strong and flexible.

5. NEARLY 20 PERCENT OF YOUR BODY IS CARBON.

May Nyman, a professor of inorganic chemistry at Oregon State University in Corvallis, Oregon tells Mental Floss that carbon has an almost unbelievable range. "It makes up all life forms, and in the number of substances it makes, the fats, the sugars, there is a huge diversity," she says. It forms chains and rings, in a process chemists call catenation. Every living thing is built on a backbone of carbon (with nitrogen, hydrogen, oxygen, and other elements). So animals, plants, every living cell, and of course humans are a product of catenation. Our bodies are 18.5 percent carbon, by weight.

And yet it can be inorganic as well, Nyman says. It teams up with oxygen and other substances to form large parts of the inanimate world, like rocks and minerals.

6. WE DISCOVERED TWO NEW FORMS OF IT ONLY RECENTLY.

Carbon is found in four major forms: graphite, diamonds, fullerenes, and graphene. "Structure controls carbon's properties," says Nyman.  Graphite ("the writing stone") is made up of loosely connected sheets of carbon formed like chicken wire. Penciling something in actually is just scratching layers of graphite onto paper. Diamonds, in contrast, are linked three-dimensionally. These exceptionally strong bonds can only be broken by a huge amount of energy. Because diamonds have many of these bonds, it makes them the hardest substance on Earth.

Fullerenes were discovered in 1985 when a group of scientists blasted graphite with a laser and the resulting carbon gas condensed to previously unknown spherical molecules with 60 and 70 atoms. They were named in honor of Buckminster Fuller, the eccentric inventor who famously created geodesic domes with this soccer ball–like composition. Robert Curl, Harold Kroto, and Richard Smalley won the 1996 Nobel Prize in Chemistry for discovering this new form of carbon.

The youngest member of the carbon family is graphene, found by chance in 2004 by Andre Geim and Kostya Novoselov in an impromptu research jam. The scientists used scotch tape—yes, really—to lift carbon sheets one atom thick from a lump of graphite. The new material is extremely thin and strong. The result: the Nobel Prize in Physics in 2010.

7. DIAMONDS AREN'T CALLED "ICE" BECAUSE OF THEIR APPEARANCE.

Diamonds are called "ice" because their ability to transport heat makes them cool to the touch—not because of their look. This makes them ideal for use as heat sinks in microchips. (Synthethic diamonds are mostly used.) Again, diamonds' three-dimensional lattice structure comes into play. Heat is turned into lattice vibrations, which are responsible for diamonds' very high thermal conductivity.

8. IT HELPS US DETERMINE THE AGE OF ARTIFACTS—AND PROVE SOME OF THEM FAKE.

American scientist Willard F. Libby won the Nobel Prize in Chemistry in 1960 for developing a method for dating relics by analyzing the amount of a radioactive subspecies of carbon contained in them. Radiocarbon or C14 dating measures the decay of a radioactive form of carbon, C14, that accumulates in living things. It can be used for objects that are as much as 50,000 years old. Carbon dating help determine the age of Ötzi the Iceman, a 5300-year-old corpse found frozen in the Alps. It also established that Lancelot's Round Table in Winchester Cathedral was made hundreds of years after the supposed Arthurian Age.

9. TOO MUCH OF IT IS CHANGING OUR WORLD.

Carbon dioxide (CO2) is an important part of a gaseous blanket that is wrapped around our planet, making it warm enough to sustain life. But burning fossil fuels—which are built on a carbon backbone—releases more carbon dioxide, which is directly linked to global warming. A number of ways to remove and store carbon dioxide have been proposed, including bioenergy with carbon capture and storage, which involves planting large stands of trees, harvesting and burning them to create electricity, and capturing the CO2 created in the process and storing it underground. Yet another approach that is being discussed is to artificially make oceans more alkaline in order to let them to bind more CO2. Forests are natural carbon sinks, because trees capture CO2 during photosynthesis, but human activity in these forests counteracts and surpasses whatever CO2 capture gains we might get. In short, we don't have a solution yet to the overabundance of C02 we've created in the atmosphere.

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8 Myths About Dead Bodies You Probably Think Are True
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Bodies are weird enough, but it's the dead ones that hold real intrigue. The fact that most of us just don't spend that much time around them means it's hard to separate truth from fiction; corpses have been thought to be responsible for plagues, as well as to carry magic healing properties. Below, some dead body myths that won't give up the ghost—and explanations for the real-life science behind them.

1. HAIR AND NAILS GROW AFTER DEATH.

Corpse under sheet with hand sticking out

Not true! The cell division driving hair and nail growth stops when the body dies and the heart no longer pumps oxygen-filled blood throughout the circulatory system. It does look like things keep growing, though. When a dead body's skin loses hydration, it retracts—and retraction along the nail bed makes it appear as if the nails are getting longer. As for hair, drying skin on the face and head "pulls back towards the skull, making stubble appear more prominent," writes Claudia Hammond for the BBC. "Goosebumps caused by the contraction of the hair muscles can add to the effect."

2. DEAD BODIES ARE DANGEROUS.

There's no science to back up the idea that a dead and decomposing body is harmful to the living just by virtue of its being dead. This might sound obvious, but the belief that disease came from breathing in air infected by corpses was once common.

Miasmatic theory, as it was called, was a widespread belief among members of the medical profession (and the public) in the 19th century. Miasma, an ancient Greek word for "pollution," was the bad air coming from "rotting corpses, the exhalations of other people already infected, sewage, or even rotting vegetation" and was thought to be responsible for the spread of disease. Fortunately, this belief was eventually replaced by germ theory.

3. … AND MULTIPLE DEAD BODIES ARE EXTRA DANGEROUS.

In a publication from the Pan American Health Organization (a division of the World Health Organization), Donna Eberwine explains that the belief that dead bodies spread disease "remains a chronic problem in disaster relief efforts." After natural disasters, there is often a hysteria around dead bodies and a rush to immediately bury them, which distracts relief efforts from more pressing concerns. "The microorganisms that are involved in decomposition are not the kind that cause disease," Eberwine writes. "And most viruses and bacteria that do cause disease cannot survive more than a few hours in a dead body."

There are some exceptions. The level of Ebola virus in dead victims remains high, and their remains should only be handled by people in protective gear (and buried quickly). HIV can live for up to 16 days in a body held under refrigeration, and other blood-borne viruses like hepatitis, along with tuberculosis and gastrointestinal infections, can pose a risk. "The risk of contagion can be minimized with basic precautions and proper hygiene," Eberwine writes.

4. EMBALMING MAKES DEAD BODIES "SAFER."

Egyptian sarcophagus

"Embalming provides no public health benefit," according to the Funeral Consumer's Alliance (a nonprofit focused on affordable death care), citing the Centers for Disease Control and Canadian authorities. While individual morticians might say that a body must be embalmed before viewing, burial, or cremation, the process is generally not legally required. Moreover, since a dead body is usually not in itself harmful, embalming does not make it any safer. On the flip side, embalming chemicals are actually quite toxic, and embalmers must cover their entire body and wear a respirator while working. 

5. DEAD BODIES SIT UP ON THE MEDICAL TABLE.

This horror-movie trope just isn't real. During decomposition, a body might twitch or make small movements and noises due to the gas and waste released by bacteria. A decomposing corpse can definitely move a little, but sitting straight up is just not going to happen.

6. BURYING A BODY WITHOUT A COFFIN OR VAULT MEANS IT WILL CONTAMINATE THE GROUNDWATER.

Nope! Burials usually occur at 3.5 feet below the surface, whereas water can be 75 feet underground. "Mandatory setbacks from known water sources also ensure that surface water is not at risk," the Green Burial Council explains [PDF]. Additionally, because microorganisms living in the soil will break down the chemical compounds that remain in a dead body, we actually give out "more toxic chemicals during a day of living than a whole body will decomposing."

7. CREMAINS ARE "ASH."

Wall of cremation urns

Though we often talk of "scattering ashes," cremains are a little more complicated. Once a body intended for cremation has been burned in what's called a retort, what's left will be put in a cremulator. Sort of like a blender, the cremulator uses ball bearings or rotating blades to pulverize the bones and other remnants into a "grayish, coarse material, like fine gravel," as HowStuffWorks puts it.

8. ALL IN ALL, MAYBE DEATH ISN'T AS SCARY AS WE THINK.

According to psychological scientist Kurt Gray, it's possible that death isn't quite as terrifying as we think it is. Gray studied the responses of death row inmates and terminally ill patients as well as those of people asked to imagine they had untreatable cancer, and found that "while it's natural to fear death in the abstract, the closer one actually gets to it, the more positive he or she becomes," as New York Magazine explains. This may be due to something called the "psychological immune system," a term coined by Harvard psychologist Dan Gilbert in his book Stumbling on Happiness. According to Gray, our psychological immune system is engaged when bad things happen. "So when one is faced with death, all sorts of rationalization and meaning-making processes come in," he told New York Magazine. That may sound like your brain's trying to give you a cop-out, but it's much better than living in terror.

All photos courtesy of iStock.

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