13 Facts About Ovaries

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iStock.com/magicmine

Ovaries are only about the size of large grapes, but they’re one of the most important organs in the female body. Their primary responsibilities include producing eggs and secreting sex hormones that promote fertility. In this way, the future of humanity depends on them. Read on to learn more about these tiny but mighty organs.

1. THEY’RE THE FEMALE GONADS.

Go ahead and laugh, but gonads was a scientific term long before it became slang for a man’s testicles. It actually refers to the reproductive glands of both sexes: ovaries for women, and testes for men. When an embryo is in the early stages of development (around the seventh week), its gonads have the potential to develop into either female or male sex organs through a process called sexual differentiation. By this point, the sex has already been pre-determined by chromosomes (XX or XY), and in the absence of a Y chromosome, the gonads turn into ovaries. One study of adult mice found that ovaries could be turned into testes by deleting a single gene called FOXL2, which is constantly working to suppress the development of male anatomy in mammals. However, it's unknown what effect the modification of this gene would have on humans.

2. THEY’RE CONTROLLED BY THE BRAIN.

The hypothalamus and pituitary gland both play pivotal roles in ensuring the ovaries function as they should. Neither is located anywhere near the ovaries, though. “If you put your finger between your eyes and shoved it backwards into your brain, first you would knock into your pituitary gland, which is a little pea-sized gland,” Randi Epstein, a New York City-based medical doctor and writer, tells Mental Floss. “And if you kept ramming backwards, then you would hit the hypothalamus.” (Of course, she doesn’t recommend actually trying this.)

The hypothalamus is the hormone control center, while the pituitary gland is called the body’s "master gland" because it controls the thyroid and adrenal glands, as well as the ovaries and testicles. Essentially, the hypothalamus tells the pituitary gland to send hormones to the ovaries, and the ovaries respond by secreting their own batch of hormones. A signal is then sent back to the hypothalamus to let it know if the levels of estrogen and progesterone are too high or too low. The cycle then continues, but we don't fully understand what triggers the hypothalamus and kicks off the process in the first place, Epstein says.

3. IT’S HARD TO ACCURATELY PREDICT WHEN OVARIES WILL KICK OFF MENOPAUSE.

Because of the previously mentioned unknowns, there’s no way of telling when puberty or menopause will occur. In the latter case, scientists have been looking at different genetic markers in an attempt to predict when the ovaries will shut down the processes of menstruation and ovulation—otherwise known as menopause—but "nothing is definitive" right now, according to Mary Jane Minkin, an obstetrician-gynecologist in New Haven, Connecticut, who also teaches at the Yale School of Medicine.

However, family history and age offer some clues. The average age for menopause in the U.S. is 51, but if all the women in your family went through menopause in their forties, there’s a good chance you will, too. Women who have had hysterectomies may also go through menopause one or two years earlier than they normally would, even if they have otherwise healthy ovaries. That's because the surgery is believed to reduce the flow of blood to the ovaries, resulting in a lower supply of hormones and therefore earlier ovarian failure.

4. SMOKING CAN ALSO TRIGGER EARLIER MENOPAUSE.

The effects of smoking on internal organs aren’t pretty, and the ovaries are no exception. “Smoking rots ovaries,” Minkin tells Mental Floss. “Basically, if you want to go through menopause earlier, smoke cigarettes.” Doing so can accelerate the onset of menopause by one to two years, and studies have shown that smoking hurts overall ovarian function as well.

5. THEY CHANGE SHAPE OVER TIME.

Ovaries get bigger and morph into the shape of an almond when girls reach adolescence, eventually reaching roughly 1.4 inches in length. Later in life, once menopause has occurred and the ovaries have fulfilled their purpose, they dwindle to under an inch long. “They just sort of poop out and they shrink, so the size gets exponentially smaller,” Minkin says.

6. WHEN A GIRL IS BORN, HER OVARIES HOLD ALL THE EGGS SHE’LL EVER HAVE ...

Female fetuses can carry as many as 7 million oocytes (immature eggs) in their ovarian follicles, and by the time they’re born, that number drops to about 2 million. Here's a mind-boggling fact: If a woman is pregnant with a girl, that means she’s also carrying her potential grandchildren, too.

Many of these eggs die off before a girl reaches reproductive age, though. By the time she starts going through puberty, she has about 300,000 left. About 1000 or so eggs are lost each month after that. When it’s all said and done, only about 400 mature eggs go through ovulation, at which point they’re dropped from the ovaries, through the fallopian tubes, and into the uterus.

7. ... BUT STEM CELL RESEARCH COULD CHANGE THAT.

Research in recent years has suggested that ovarian stem cells could someday be used to grow new egg cells, or to delay or stop menopause in women. Both of these tasks have already been successfully carried out in mice. "If we could gain control of the [human] female biological clock ... you could arguably delay the time of ovary failure, the primary force behind menopause,” researcher Jonathan Tilly told National Geographic in 2012.

For now, women faced with a diminishing supply can have their unfertilized eggs frozen through the process of cryopreservation. It’s meant to improve a woman’s chances of conceiving at a later date, but it isn’t guaranteed to work. “It’s getting better, but it’s hardly perfect,” Minkin says. “You can freeze the eggs, but you don’t know how viable they’re going to be in the long-term.”

8. SCIENTISTS HAVE CREATED 3D-PRINTED OVARIES FOR MICE.

In 2017, scientists used “porous scaffolds from a gelatin ink” to 3D-print synthetic ovaries for mice, The Guardian reported. Those ovaries were then filled with follicles containing immature egg cells, which allowed the mice to give birth to healthy babies. Scientists hope this technique will someday be used to restore fertility to women whose ovaries have been damaged by cancer treatments.

9. OVARIES CHILL OUT ON BIRTH CONTROL PILLS.

Oral contraceptives prevent ovulation by providing all the estrogen and progesterone that the body needs. With the ovaries’ job taken care of, they get to go on “vacation,” Minkin says. When contraceptive pills are used for five or more years, they reduce a woman’s risk of ovarian cancer by 50 percent. That’s because “funky things can happen” during ovulation, at which time the ovaries are at greater risk of an aberration, Minkin says. On the other hand, if the ovaries aren’t releasing eggs, there’s less of an opportunity for mistakes to happen. The ovaries are also less exposed to naturally occurring hormones that may promote the growth of cancer.

10. SOME CHRONIC CONDITIONS AFFECT THE OVARIES.

One of the most common problems affecting the ovaries are cysts. These fluid-filled sacs can form when an egg isn’t properly released from an ovarian follicle, or if the empty follicle sac doesn’t shrink after it bursts open to release an egg. Fortunately, these cysts often go away on their own. They only become a problem if they grow, or multiple cysts form. Strange things can happen, though. In one recent case, surgeons found a cyst containing a miniature skull and brain tissue inside the ovary of a 16-year-old girl. Yes, you read that right. It's called a teratoma —from the Greek word for monster—and it happens when the reproductive cells go rogue and start developing their own way.

Another disorder that can sometimes affect the ovaries is endometriosis. This occurs when tissue that’s similar to the endometrium, which lines the uterus, starts growing somewhere outside the uterus and causes a chronic inflammatory reaction. It can attach to the bladder, bowel, ovaries, or other areas. Symptoms may be minimal, severe, or somewhere in between, and the tissue can be removed through a minor surgery if needed.

Polycystic ovary syndrome (PCOS) is another fairly common problem, and it’s caused by a hormonal imbalance that in turn creates problems for the ovaries. Ovulation may not go as smoothly, periods can be irregular, and cysts can develop. Since there’s no cure, it’s a lifelong condition, but the symptoms can be managed.

11. CUNNING SALESMEN ONCE SOLD ANTI-AGING OVARY TONICS.

Miracle elixirs made from animal ovaries and testes were a big “money-making fad” in the early 20th century, Epstein writes in her book Aroused: The History of Hormones and How They Control Just About Everything. According to the sales pitch at the time, sex organs give life, so it’s only logical that they would help boost your energy and libido. “We were taking rabbit ovaries, crushing them up, desiccating them, and using them as a fertility or anti-aging treatment,” Epstein tells Mental Floss. One of the first “cures” for menopause and menstruation symptoms wasn’t much better, either. The main active ingredient was alcohol.

12. BIRDS HAVE JUST ONE FUNCTIONAL OVARY.

Unlike their dinosaur ancestors, birds have only their left ovary. Scientists theorize that birds lost an ovary over the course of evolution because it helped reduce their weight, making it easier for them to fly. This explains why dinosaurs laid loads of eggs, but birds lay just a few at a time.

13. SOME ANIMALS CAN SWITCH SEXES BY CHANGING THEIR OVARIES.

All clownfish are born male, but they’re able to change sex at will. This is because they have both mature testes and immature ovaries, the latter of which can develop if the alpha female in a school of fish dies. (As Business Insider points out, a scientifically accurate Finding Nemo would have been significantly more disturbing.)

Parrotfish can change sex as well—mostly from female to male. During this transition, the ovaries dissolve and testes are grown. “In general, for species where big males can control access to females (think harem), it pays to be female when small (you get to reproduce with the dominant male) and then turn into a male when you are big enough to duke it out with a competing male to win access to a group of females,” writes Marah Hardt, author of Sex in the Sea.

11 Squeaky-Clean Facts About Spit

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iStock/fotolinchen

Though most people find the thought of saliva rather disgusting, spit plays a vital role in our lives. It allows us to comfortably chew, swallow, and digest. It fights off bacteria in our mouths and elsewhere, and leads the mouth’s bold fight against cavities. Here are 11 facts that might have you reconsidering that unsung hero of bodily fluids: spit.

1. Spit is mostly water.

Saliva consists of about 99 percent water. The other 1 percent is made up of electrolytes and organic substances, including digestive enzymes and small quantities of uric acid, cholesterol, and mucins (the proteins that form mucus).

2. There's a medical standard for how much spit you should have.

Healthy individuals accumulate between 2 and 6 cups of spit a day. That’s without stimulation from activities like eating or chewing gum, which open the spit floodgates [PDF].

3. Saliva production has a circadian rhythm.

Your body typically produces the most saliva in the late afternoon, and the least at night. Salivation is controlled by the autonomic nervous system (much like your heartbeat), meaning it’s an unconscious process.

4. There are five different kinds of spit.

Salivation has five distinct phases, most triggered by the passage of food through the body. Not all of them are a good thing. The first type of salivation is cephalic, the kind that occurs when you see or smell something delicious. The buccal phase is the body’s reflexive response to the actual presence of food in the mouth (which aids in swallowing). The esophageal involves the stimulation of the salivary glands as food moves through the esophagus. The gastric phase happens when something irritates your stomach—like when you’re just about to puke. The intestinal phase is triggered by a food that doesn’t agree with you passing through the upper intestine.

5. Spit can battle bacteria.

There’s a reason the phrase “lick your wounds” came about. Spit is full of infection-battling white blood cells. And, according to a 2015 study in the journal Blood, neutrophils—a type of white blood cell—are more effective at killing bacteria if they come from saliva than from anywhere else in the body. So adding saliva to a wound gives the body a powerful backup as it fights off infection.

6. Spit keeps you from getting cavities.

The calcium, fluoride, and phosphate in saliva strengthen your teeth. Spit also fights cavity-causing bacteria, washes away bits of food, and neutralizes plaque acids, reducing tooth decay and cavities. That’s why chewing gum gets dentists’ stamp of approval—chewing increases the flow of saliva, thus protecting your oral health.

7. You need spit if you want to taste anything.

Saliva acts like a solvent for tastes, ferrying dissolved deliciousness to the sites of taste receptors. It also keeps those receptors healthy by preventing them from drying out and protecting them from bacterial infection. Many people who have dry mouth (or xerostomia) find their sense of taste affected by their oral cavity’s parched conditions. Because many medications have dry mouth as a side effect, scientists have developed artificial saliva sprays that mimic the lubrication of real spit.

8. Swapping spit exchanges millions of bacteria.

A 10-second kiss involves the transfer of some 80 million bacteria, one study found.

9. People aren’t born drooling.

Babies don’t start drooling until they’re 2 to 4 months old. Unfortunately, they also don’t really know what to do with their spit. They don’t have full control of the muscles of their mouth until they’re around 2 years old, so they can’t really swallow it effectively. Which is why we invented bibs.

10. Stress can leave you spit-less.

The body’s fight-or-flight response is designed to give you the energy and strength needed to overcome a near-death experience, like, say, running into a bear or giving a big presentation at work. Your blood pressure goes up, the heart beats faster, and the lungs take in more oxygen. This is not the time to sit around and digest a meal, so the digestion system slows down production, including that of saliva.

11. A lack of spit was once used as an admission of guilt.

In some ancient societies, saliva was used as a basic lie detector. In ancient India, accused liars had to chew grains of rice. If they were telling the truth, they would have enough saliva to spit them back out again. If someone was lying, their mouth would go dry and the rice would stick in their throat.

13 Facts About Genes

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iStock.com/IPGGutenbergUKLtd, stock_colors, RapidEye, b-d-s

In 2003, after 13 years of study, international researchers working on the groundbreaking Human Genome Project published their findings. For the very first time, the genetic building blocks that make up humans were mapped out, allowing researchers “to begin to understand the blueprint for building a person,” according to the project's website. Humans are now known to have between 20,000 and 25,000 genes, but researchers still have much to learn about these small segments of DNA. Below, we’ve listed a few facts about gene expression, genetic diseases, and the ways genes make us who we are.

1. The word gene wasn’t coined until the 20th century.

Although “father of genetics” Gregor Mendel conducted his pea plant experiments in the mid-1800s, it wasn’t until 1909 that Danish botanist Wilhelm Johannsen became the first person to describe Mendel's individual units of heredity. He called them genes—derived from pangenesis, the word Charles Darwin used for his now-disproven theory of heredity (among other ideas, Darwin suggested that acquired characteristics could be inherited).

2. On a genetic level, all humans are more than 99 percent identical.

Humans have a lot more in common than we might be inclined to believe. In fact, more than 99 percent of our genes are exactly the same from one person to the next. In other words, the diversity we see within the human population—including traits like eye color, height, and blood type—is due to genetic differences that account for less than 1 percent. More specifically, variations of the same gene, called alleles, are responsible for these differences.

3. Genes can disappear or break as species evolve.

Thanks to a combination of genes, most mammals are able to biologically produce their own Vitamin C in-house, so to speak. But some point throughout the course of human history, we lost the ability to make Vitamin C when one of those genes stopped functioning in humans long ago. “You can see it in our genome. We are missing half the gene,” Dr. Michael Jensen-Seaman, a genetics researcher and associate professor of biological sciences at Duquesne University in Pittsburgh, tells Mental Floss. “Generally speaking, when a species loses a gene during evolution, it’s usually because they don’t need it—and if you don’t use it, you lose it. All our ancestors probably ate so much fruit that there was never any need to make your own Vitamin C.” Jensen-Seaman says humans also lost hundreds of odorant receptors (proteins produced by genes that detect specific smells) because we rely mostly on vision. This explains why our sense of smell is worse than many other species.

4. Elizabeth Taylor’s voluminous eyelashes were likely caused by a genetic mutation.

A mutation of the aptly named FOXC2 gene gave Hollywood icon Elizabeth Taylor two rows of eyelashes. The technical term for this rare disorder is distichiasis, and while it may seem like a desirable problem to have, there can be complications. According to the American Academy of Ophthalmology, this extra set of lashes is sometimes “fine and well tolerated,” but in other cases they should be removed to prevent eye damage.

5. Genes involved in sperm are some of the most rapidly evolving genes in the animal kingdom.

Throughout much of the natural world, a class of genes called sperm competition genes are becoming better and better at fertilizing eggs. This is true for various species, including some primates and marine invertebrates. Consider promiscuous primates, like chimpanzees, whose females mate with multiple males in a short period of time. As a result, the males are competing at the genetic level—via their sperm—to father offspring. “What’s happening, we think, is there’s sort of an arms race among genes that are involved in either sperm production or any aspect of male reproduction,” Jensen-Seaman says. Essentially, the proteins in these genes are changing to help males rise to the occasion.

6. A “zombie gene” in elephants might help protect them from cancer.

In a 2018 study published in Cell Reports, researchers from the University of Chicago found that a copy of a cancer-suppressing gene that was previously “dead” (or non-functioning) in elephants turned back on at some point. They don’t know why or how it happened, but this reanimated “zombie gene” might explain why elephants have such low rates of cancer—just 5 percent die from the disease, compared to 11 to 25 percent of humans. Some have suggested that a drug could theoretically be created to mimic the function of this gene in order to treat cancer in humans.

7. Octopuses can edit their own genes.

Cephalopods like squids, cuttlefish, and octopuses are incredibly intelligent and wily creatures—so much so that they can rewrite the genetic information in their neurons. Instead of one gene coding for one protein, which is normally the case, a process called recoding lets one octopus gene produce multiple proteins. Scientists discovered that this process helps some Antarctic species “keep their nerves firing in frigid waters,” The Washington Post notes.

8. The premise of the 1986 film The Fly isn’t completely absurd.

After a botched experiment in The Fly, Jeff Goldblum morphs into a fly-like creature. Surprisingly, that premise might, uh, fly—at least on some genetic level. Although different researchers come up with different estimates, humans share about 52 percent of the same genes with fruit flies, and scientists figure that the number is roughly the same for house flies.

So, could Jeff Goldblum theoretically turn into a human-fly hybrid if his genes got mixed up with the insect's in a futuristic teleportation device? Not exactly, but there are some scientific parallels. “With genetic engineering, we can select genes and insert them into other organisms’ genomes,” DNA researcher Erica Zahnle tells the Chicago Tribune. “We do it all the time. Right now there’s a hybrid of a tomato that has a fish gene in it.”

9. Our genes might prevent us from living more than 125 years.

Despite advances in medicine, there might be a biological cap on how long humans can stick around. Several studies have suggested that we’ve already peaked, with the maximum extent for human life falling between 115 and 125 years. According to this theory, cells can only replicate so many times, and they often become damaged with age. Even if we’re able to modify our genes via gene therapy, we probably can’t modify them fast enough to make much of a difference, Judith Campisi from the Buck Institute for Research on Aging tells The Atlantic.

“For such reasons, it is meaningless to claim that most human will live for 200–500 years in the near future, thanks to medical or scientific progress, or that ‘within 15 years, we'll be adding more than a year every year to our remaining life expectancy,’” the authors of a 2017 study write in Frontiers in Physiology, citing previous studies from 2003 and 2010, respectively. “Raising false hopes without taking into account that human beings are already extremely ‘optimized’ for lifespan seems inappropriate.”

10. The idea that a single gene determines whether you have attached or unattached earlobes is a myth.

Forget what you may have learned about earlobes and genetics in middle school. While your genes probably play some role in determining whether you have attached earlobes (a supposedly dominant trait) or unattached earlobes, the idea that this trait is controlled by a single gene is simply untrue. On top of that, earlobes don’t even fall into two distinct categories. There’s also a third, which University of Delaware associate professor John H. McDonald calls intermediate earlobes. "It doesn't look to me as if there are just two categories; instead, there is continuous variation in the height of the attachment point," McDonald writes on his website. A better example of a trait controlled by a single gene is blood type. Whether you have an A, B, or O blood type is determined by three variations—or alleles—of one gene, according to Jensen-Seaman.

11. No, there isn’t a "wanderlust gene" or "music gene."

Every now and then, new studies will come out that seem to suggest a genetic source for various personality traits, preferences, or talents. In 2015, there was talk of a “wanderlust gene” that inspires certain people to travel, and several other reports have suggested musical aptitude is also inherited. However, like many things in science, the reality isn’t so simple. “Part of the problem is that when we’re in school, we learn examples of traits that are controlled by a single gene, like Mendel’s peas, and we start to think that all variation is determined by a single gene,” Jensen-Seaman says. “But other than a variety of rare genetic diseases, most of the interesting things in medicine, or in human behavior or human variation, are what we call complex traits.” These complex traits typically involve hundreds—if not thousands—of genes, as well as the environmental factors you’re exposed to throughout your life.

12. DNA testing kits can’t tell how smart you are.

Much like your talents and personality, intelligence is also a complex trait that's difficult to measure because it’s influenced by many different genes. One 2017 study identified 52 genes associated with higher or lower intelligence, but the predictive power of those genes—or ability to tell how smart you are—is less than 5 percent. Another study from 2018 identified 538 genes associated with intelligence, which have a 7 percent predictive power. Put simply, no DNA testing kit can accurately predict whether you're a genius or dunce, even if the company claims it can. And, even if scientists make improvements in this field of study, DNA tests can't account for the environmental factors that also influence intelligence.

13. Your genetic makeup determines whether you think your pee smells funky after eating asparagus.

Do you recoil from the scent of your urine after eating asparagus? If so, you’re among the nearly 40 percent of people who are able to detect the smell of metabolized asparagus in pee, according to a study of nearly 7000 people of European-American descent that was published in The BMJ's 2016 Christmas issue. (The BMJ has an annual tradition of publishing strange and light-hearted studies around this time of year, and the asparagus pee study is no exception.) Again, there isn’t one gene in particular to pin the blame on, though. Multiple olfactory receptor genes—and 871 sequence variations on said genes—are involved in determining whether you have a talent for sniffing out asparagus pee.

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