11 Facts About the Kidneys

iStock.com/Davizro
iStock.com/Davizro

Kidneys are kind of like the Brita filters of the human body. Each of these bean-shaped organs is only about the size of a fist, but they serve several vital functions. In addition to ridding your body of waste, the kidneys also help make red blood cells and regulate your blood pressure. If they aren’t kept healthy, though, they can cause a variety of kidney disease symptoms, from kidney stones to infections that could require a kidney transplant. Here are 11 facts you might not know.

1. Your pair of kidneys is lopsided.

Kidneys are located in the lower back—right below the rib cage—and they’re usually asymmetrical. Your right kidney tends to be smaller and sit a little lower than your left one because it needs to make room for the liver, whose bulkiest part is situated on the right side of your body. Your left kidney, on the other hand, has some more room to sprawl out below the spleen, an organ of smaller stature.

2. There’s a reason why you only need one kidney to live.

Most people have two kidneys at birth, but only one kidney is needed to lead a healthy life. Each kidney has about 1.5 million blood-filtering units called nephrons, which help remove a waste product called urea from blood as it flows through the organs. People only need a minimum of 300,000 nephrons to filter blood properly, and one kidney is more than enough to fulfill this purpose. (People without healthy kidneys can survive with dialysis, a process where blood is filtered by machine, or opt for a kidney transplant.)

3. Your kidneys filter about 45 gallons of blood per day.

Although the heart is responsible for pumping blood throughout the body, the kidneys are doing their fair share of work, too. They filter a half-cup of blood every minute, which works out to be 45 gallons of blood per day—or enough to fill a small bathtub.

4. Kidneys make pee.

As part of the body’s urinary system, kidneys create urine from urea, water, and other waste products. The fluid flows from the kidney’s tubules, which are found inside the nephrons, to two tubes called ureters. The ureters then release the urine into the bladder—and you know what happens from there. But if problems occur, the urine can get backed up and cause kidney infections. In addition, in cases where minerals in the urine crystallize, kidney stones can form.

5. Ancient Egyptians may have been the first people to describe kidneys.

Prior to 2018, it was commonly thought that ancient Egyptians had no knowledge of the kidneys, even though their understanding of medicine and the human body was advanced in other ways. That changed when an Egyptian papyrus dating back some 3500 years revealed otherwise. It contained the world’s first known description of the kidneys, among other medical insights.

6. Kidneys are mentioned frequently in the Bible.

The kidneys are cited more than 30 times in the Bible—far more frequently than the heart, which was rarely mentioned. According to a 2005 article in the Journal of the American Society of Nephrology by Baylor College of Medicine professor Garabed Eknoyan, it was not uncommon for symbolic meaning to be ascribed to various organs in ancient Middle Eastern texts. “Unlike most ancient literature, however, the kidneys receive special attention in the Bible as the seat of conscience, emotions, desire, and wisdom,” Eknoyan wrote. “The broader region of the loins, which according to the Oxford English Dictionary is implied in the now archaic term ‘reins,’ is considered the site of physical strength and prowess.”

7. A procedure for removing kidney stones used to be deadly.

These days, if a patient is unable to pass a kidney stone naturally (albeit painfully), laser and high-frequency sound wave treatments can be used to break the hard mineral deposits into smaller pieces. For much of history, though, a patient’s only option was to go under the knife. Kidney stone surgeries were common from the 16th to 18th centuries, and one of the procedures involved cutting open the perineum, inserting a cutting instrument into the bladder, and chopping up the stone manually. Self-taught surgeon Frère Jacques Beaulieu came up with this technique, but it wasn’t without serious risk. In 1698, 25 of the 60 patients he operated on died.

8. A Dutch doctor used sausage casing, orange juice cans, and a washing machine to invent an "artificial kidney" that predated dialysis.

At the start of World War II, not long after Germany invaded the Netherlands, Dutch doctor Willem Kolff got to work inventing an artificial kidney that evolved into modern-day dialysis. Because supplies were limited during the war, he wrapped semipermeable sausage casings around a wooden drum to create his kidney machine. A patient’s blood was pumped into the casings, and the drum was rotated to remove impurities. Later, he improved his invention by adding orange juice cans and a washing machine to the mix. Some of his earliest patients with kidney failure died after a few days, but in 1945, one woman lived seven more years thanks to Kolff’s machine. When Kolff wasn’t busy creating artificial organs, he was saving lives in other ways: He also established Europe’s first blood blank and helped more than 800 people avoid Nazi concentration camps by hiding them in his hospital.

9. Drinking too much water can be bad for kidneys.

Staying hydrated helps keep your kidneys in good working order, but on the flip side, you don’t want to drink too much water. Doing so can cause a condition called hyponatremia, which occurs when the sodium in the blood becomes diluted because the kidneys can’t get rid of the fluid fast enough. The condition can be severe, causing swelling of the cells. It's uncommon, though, and it mainly occurs among athletes who overexert their bodies and drink extra water to compensate. So how much water is the right amount? It varies from person to person, but the Health and Medicine Division of the National Academies of Sciences, Engineering, and Medicine suggests that women drink around 9 cups (2.2 liters) per day, and that men drink about 13 cups (3 liters).

10. Too much ibuprofen and aspirin can also harm kidneys.

All drugs pass through your kidneys, so you want to be careful what you’re feeding them. If used daily for long periods of time, pain medications like ibuprofen, higher-dose aspirin, and naproxen (Aleve) can damage kidneys and potentially cause a disease called chronic interstitial nephritis. However, taking a daily low-dose aspirin to prevent heart attacks has no effect on kidney function.

11. Climate change may be causing an uptick in chronic kidney disease.

Recent research shows that chronic kidney disease is becoming more prevalent in Central America and parts of Asia, especially among manual laborers who spend most of their day outdoors. Although diabetes and high blood pressure are the main causes of impaired kidney function, these factors were ruled out among workers in El Salvador, Sri Lanka, India, and other countries. Other environmental factors may be involved, but researchers say the extreme heat is largely to blame—and climate change is only making it worse. For one, the more someone sweats, the more dehydrated they become. Over time, this can result in severe kidney damage.

“This can be considered the first disease that’s related to climate change,” Dr. Roberto Lucchini, an environmental medicine and public health professor at Mount Sinai’s Icahn School of Medicine in New York City, tells Mental Floss. He says the problem is so severe in Guatemala that job applicants’ creatinine levels are tested before they’re hired to work an outdoor job. Creatinine is a waste product that gets removed from blood by the kidneys, and if those levels are too high, it could signal a greater risk of kidney disease. Two other studies suggest the problem is even starting to affect outdoor workers in warmer parts of the U.S., including California and Florida. “If this continues as a general trend towards increased temperature, this is concerning,” Lucchini says.

10 Products for a Better Night's Sleep

Amazon/Comfort Spaces
Amazon/Comfort Spaces

Getting a full eight hours of sleep can be tough these days. If you’re having trouble catching enough Zzzs, consider giving these highly rated and recommended products a try.

1. Everlasting Comfort Pure Memory Foam Knee Pillow; $25

Everlasting Comfort Knee Pillow
Everlasting Comfort/Amazon

For side sleepers, keeping the spine, hips, and legs aligned is key to a good night’s rest—and a pain-free morning after. Everlasting Comfort’s memory foam knee pillow is ergonomically designed to fit between the knees or thighs to ensure proper alignment. One simple but game-changing feature is the removable strap, which you can fasten around one leg; this keeps the pillow in place even as you roll at night, meaning you don’t have to wake up to adjust it (or pick it up from your floor). Reviewers call the pillow “life-changing” and “the best knee pillow I’ve found.” Plus, it comes with two pairs of ear plugs.

Buy it: Amazon

2. Letsfit White Noise Machine; $21

Letsfit White Noise Machine
Letsfit/Amazon

White noise machines: They’re not just for babies! This Letsfit model—which is rated 4.7 out of five with nearly 3500 reviews—has 14 potential sleep soundtracks, including three white noise tracks, to better block out everything from sirens to birds that chirp enthusiastically at dawn (although there’s also a birds track, if that’s your thing). It also has a timer function and a night light.

Buy it: Amazon

3. ECLIPSE Blackout Curtains; $16

Eclipse Black Out Curtains
Eclipse/Amazon

According to the National Sleep Foundation, too much light in a room when you’re trying to snooze is a recipe for sleep disaster. These understated polyester curtains from ECLIPSE block 99 percent of light and reduce noise—plus, they’ll help you save on energy costs. "Our neighbor leaves their backyard light on all night with what I can only guess is the same kind of bulb they use on a train headlight. It shines across their yard, through ours, straight at our bedroom window," one Amazon reviewer who purchased the curtains in black wrote. "These drapes block the light completely."

Buy it: Amazon

4. JALL Wake Up Light Sunrise Alarm Clock; $38

JALL Wake Up Light Sunrise Alarm Clock
JALL/Amazon

Being jarred awake by a blaring alarm clock can set the wrong mood for the rest of your day. Wake up in a more pleasant way with this clock, which gradually lights up between 10 percent and 100 percent in the 30 minutes before your alarm. You can choose between seven different colors and several natural sounds as well as a regular alarm beep, but why would you ever use that? “Since getting this clock my sleep has been much better,” one reviewer reported. “I wake up not feeling tired but refreshed.”

Buy it: Amazon

5. Philips SmartSleep Wake-Up Light; $200

Philips SmartSleep Wake-Up Light
Philips/Amazon

If you’re looking for an alarm clock with even more features, Philips’s SmartSleep Wake-Up Light is smartphone-enabled and equipped with an AmbiTrack sensor, which tracks things like bedroom temperature, humidity, and light levels, then gives recommendations for how you can get a better night’s rest.

Buy it: Amazon

6. Slumber Cloud Stratus Sheet Set; $159

Stratus sheets from Slumber Cloud.
Slumber Cloud

Being too hot or too cold can kill a good night’s sleep. The Good Housekeeping Institute rated these sheets—which are made with Outlast fibers engineered by NASA—as 2020’s best temperature-regulating sheets.

Buy it: SlumberCloud

7. Comfort Space Coolmax Sheet Set; $29-$40

Comfort Spaces Coolmax Sheets
Comfort Spaces/Amazon

If $159 sheets are out of your price range, the GHI recommends these sheets from Comfort Spaces, which are made with moisture-wicking Coolmax microfiber. Depending on the size you need, they range in price from $29 to $40.

Buy it: Amazon

8. Coop Home Goods Eden Memory Foam Pillow; $80

Coop Eden Pillow
Coop Home Goods/Amazon

This pillow—which has a 4.5-star rating on Amazon—is filled with memory foam scraps and microfiber, and comes with an extra half-pound of fill so you can add, or subtract, the amount in the pillow for ultimate comfort. As a bonus, the pillows are hypoallergenic, mite-resistant, and washable.

Buy it: Amazon

9. Baloo Weighted Blanket; $149-$169

Baloo Weighted Blanket
Baloo/Amazon

Though the science is still out on weighted blankets, some people swear by them. Wirecutter named this Baloo blanket the best, not in small part because, unlike many weighted blankets, it’s machine-washable and -dryable. It’s currently available in 12-pound ($149) twin size and 20-pound ($169) queen size. It’s rated 4.7 out of five stars on Amazon, with one reviewer reporting that “when it's spread out over you it just feels like a comfy, snuggly hug for your whole body … I've found it super relaxing for falling asleep the last few nights, and it looks nice on the end of the bed, too.” 

Buy it: Amazon 

10. Philips Smartsleep Snoring Relief Band; $200

Philips SmartSleep Snoring Relief Band
Philips/Amazon

Few things can disturb your slumber—and that of the ones you love—like loudly sawing logs. Philips’s Smartsleep Snoring Relief Band is designed for people who snore when they’re sleeping on their backs, and according to the company, 86 percent of people who used the band reported reduced snoring after a month. The device wraps around the torso and is equipped with a sensor that delivers vibrations if it detects you moving to sleep on your back; those vibrations stop when you roll onto your side. The next day, you can see how many hours you spent in bed, how many of those hours you spent on your back, and your response rate to the vibrations. The sensor has an algorithm that notes your response rate and tweaks the intensity of vibrations based on that. “This device works exactly as advertised,” one Amazon reviewer wrote. “I’d say it’s perfect.”

Buy it: Amazon

This article contains affiliate links to products selected by our editors. Mental Floss may receive a commission for purchases made through these links.

30 Pungent Facts About Farts

This man is clearly not trying to hide the fact he just passed gas.
This man is clearly not trying to hide the fact he just passed gas.
BrilliantEye/iStock via Getty Images

Whether you openly admit it or desperately try to hide it, it’s an undeniable fact that every living and breathing human being farts. And while passing what you thought was going to be silent gas only to be wrong in certain situations can definitely be embarrassing, there’s something undeniably humorous about flatulence—no matter your age.

If you do love a good fart joke, you’re in good company. The very first recorded joke, which was written by the Sumerians and dates all the way back to 1900 BCE, was about—you guessed it—breaking wind. And some of the world's great thinkers, from William Shakespeare to J.D. Salinger, have slipped a fart joke (or 10) into their work.

In this episode of The List Show, we're sniffing out 30 fascinating facts about farts—from why humans expel gas to how often the average adult squeezes the cheese. You can watch the full episode below.

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