13 Facts About Ovaries

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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.

25 Amazing Facts About the Human Body

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iStock.com/kali9

The human body is an amazing piece of machinery—with a few weird quirks.

  1. It’s possible to brush your teeth too aggressively. Doing so can wear down enamel and make teeth sensitive to hot and cold foods.

  2. Goose bumps evolved to make our ancestors’ hair stand up, making them appear more threatening to predators.

Woman's legs with goosebumps
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  1. Wisdom teeth serve no purpose. They’re left over from hundreds of thousands of years ago. As early humans’ brains grew bigger, it reduced space in the mouth, crowding out this third set of molars.

  2. Scientists aren't exactly sure why we yawn, but it may help regulate body temperature.

  3. Your fingernails don’t actually grow after you’re dead.

  4. If they were laid end to end, all of the blood vessels in the human body would encircle the Earth four times.

  5. Humans are the only animals with chins.

    An older woman's chin
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    1. As you breathe, most of the air is going in and out of one nostril. Every few hours, the workload shifts to the other nostril.

    2. Blood makes up about 8 percent of your total body weight.

    3. The human nose can detect about 1 trillion smells.

    4. You have two kidneys, but only one is necessary to live.

    5. Belly buttons grow special hairs to catch lint.

      A woman putting her hands in a heart shape around her belly button
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      1. The satisfying sound of cracking your knuckles comes from gas bubbles bursting in your joints.

      2. Skin is the body’s largest organ and can comprise 15 percent of a person’s total weight.

      3. Thumbs have their own pulse.

      4. Your tongue is made up of eight interwoven muscles, similar in structure to an elephant’s trunk or an octopus’s tentacle.

      5. On a genetic level, all human beings are more than 99 percent identical.

        Identical twin baby boys in striped shirts
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        1. The foot is one of the most ticklish parts of the body.

        2. Extraocular muscles in the eye are the body’s fastest muscles. They allow both of your eyes to flick in the same direction in a single 50-millisecond movement.

        3. A surgical procedure called a selective amygdalohippocampectomy removes half of the brain’s amygdala—and with it, the patient’s sense of fear.

        4. The pineal gland, which secretes the hormone melatonin, got its name from its shape, which resembles a pine nut.

        5. Hair grows fast—about 6 inches per year. The only thing in the body that grows faster is bone marrow.

          An African-American woman drying her hair with a towel and laughing
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          1. No one really knows what fingerprints are for, but they might help wick water away from our hands, prevent blisters, or improve touch.

          2. The heart beats more than 3 billion times in the average human lifespan.

          3. Blushing is caused by a rush of adrenaline.

12 Intriguing Facts About the Intestines

When we talk about the belly, gut, or bowels, what we're really talking about are the intestines—long, hollow, coiled tubes that comprise a major part of the digestive tract, running from the stomach to the anus. The intestines begin with the small intestine, divided into three parts whimsically named the duodenum, jejunum, and ileum, which absorb most of the nutrients from what we eat and drink. Food then moves into the large intestine, or colon, which absorbs water from the digested food and expels it into the rectum. That's when sensitive nerves in your rectum create the sensation of needing to poop.

These organs can be the source of intestinal pain, such as in irritable bowel syndrome, but they can also support microbes that are beneficial to your overall health. Here are some more facts about your intestines.

1. The intestines were named by medieval anatomists.

Medieval anatomists had a pretty good understanding of the physiology of the gut, and are the ones who gave the intestinal sections their names, which are still used today in modern anatomy. When they weren't moralizing about the organs, they got metaphorical about them. In 1535, the Spanish doctor Andrés Laguna noted that because the intestines "carry the chyle and all the excrement through the entire region of the stomach as if through the Ocean Sea," they could be likened to "those tall ships which as soon as they have crossed the ocean come to Rouen with their cargoes on their way to Paris but transfer their cargoes at Rouen into small boats for the last stage of the journey up the Seine."

2. Leonardo da Vinci believed the intestines helped you breathe.

Leonardo mistakenly believed the digestive system aided respiratory function. In 1490, he wrote in his unpublished notebooks, "The compressed intestines with the condensed air which is generated in them, thrust the diaphragm upwards; the diaphragm compresses the lungs and expresses the air." While that isn't anatomically accurate, it is true that the opening of the lungs is helped by the relaxation of stomach muscles, which does draw down the diaphragm.

3. Your intestines could cover two tennis courts ...

Your intestines take up a whole lot of square footage inside you. "The surface area of the intestines, if laid out flat, would cover two tennis courts," Colby Zaph, a professor of immunology in the department of biochemistry and molecular biology at Melbourne's Monash University, tells Mental Floss. The small intestine alone is about 20 feet long, and the large intestine about 5 feet long.

4. ... and they're pretty athletic.

The process of moving food through your intestines requires a wave-like pattern of muscular action, known as peristalsis, which you can see in action during surgery in this YouTube video.

5. Your intestines can fold like a telescope—but that's not something you want to happen.

Intussusception is the name of a condition where a part of your intestine folds in on itself, usually between the lower part of the small intestine and the beginning of the large intestine. It often presents as severe intestinal pain and requires immediate medical attention. It's very rare, and in children may be related to a viral infection. In adults, it's more commonly a symptom of an abnormal growth or polyp.

6. Intestines are very discriminating.

"The intestines have to discriminate between good things—food, water, vitamins, good bacteria—and bad things, such as infectious organisms like viruses, parasites and bad bacteria," Zaph says. Researchers don't entirely know how the intestines do this. Zaph says that while your intestines are designed to keep dangerous bacteria contained, infectious microbes can sometimes penetrate your immune system through your intestines.

7. The small intestine is covered in "fingers" ...

The lining of the small intestine is blanketed in tiny finger-like protrusions known as villi. These villi are then covered in even tinier protrusions called microvilli, which help capture food particles to absorb nutrients, and move food on to the large intestine.

8. ... And you can't live without it.

Your small intestine "is the sole point of food and water absorption," Zaph says. Without it, "you'd have to be fed through the blood."

9. The intestines house your microbiome. 

The microbiome is made up of all kinds of microorganisms, including bacteria, viruses, fungi, and protozoans, "and probably used to include worm parasites too," says Zaph. So in a way, he adds, "we are constantly infected with something, but it [can be] helpful, not harmful."

10. Intestines are sensitive to change.

Zaph says that many factors change the composition of the microbiome, including antibiotics, foods we eat, stress, and infections. But in general, most people's microbiomes return to a stable state after these events. "The microbiome composition is different between people and affected by diseases. But we still don't know whether the different microbiomes cause disease, or are a result in the development of disease," he says.

11. Transferring bacteria from one gut to another can transfer disease—or maybe cure it.

"Studies in mice show that transplanting microbes from obese mice can transfer obesity to thin mice," Zaph says. But transplanting microbes from healthy people into sick people can be a powerful treatment for some intestinal infections, like that of the bacteria Clostridium difficile, he adds. Research is pouring out on how the microbiome affects various diseases, including multiple sclerosis, Parkinson's, and even autism.

12. The microbes in your intestines might influence how you respond to medical treatments.

Some people don't respond to cancer drugs as effectively as others, Zaph says. "One reason is that different microbiomes can metabolize the drugs differently." This has huge ramifications for chemotherapy and new cancer treatments called checkpoint inhibitors. As scientists learn more about how different bacteria metabolize drugs, they could possibly improve how effective existing cancer treatments are.

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