99 Fun Facts About Kidneys

An adult human kidney is about the size of which of these?

A fist: each kidney is only about 12 cm long, yet a person can live a full, healthy life with just one, which is what makes living kidney donation possible.

Which tube carries urine from each kidney to the bladder?

Ureter: each one is a thin tube of muscle that pushes urine down to the bladder with regular contractions, while the similar-sounding urethra is the single exit tube.

Which organ's bulk pushes the right kidney slightly lower than the left?

Liver: it sits directly over the right kidney, and the narrow gap between the two is one of the first spots emergency doctors scan for internal bleeding.

Approximately how many nephrons does each adult human kidney contain?

About 1 million in each kidney at 20, but they are not for life: healthy kidneys lose them steadily, and donors studied in their seventies had only about half as many.

About what share of the blood pumped by the heart flows through the kidneys?

About 20%, and up to a quarter: a vast share for two organs that make up under 1% of body weight, because they need the flow to filter the blood, about half a cup every minute.

Most of the roughly 180 litres the kidneys filter each day ends up where?

Back in the blood: the kidney's tubules reclaim almost all of what is filtered, so only one to two litres a day actually leave the body as urine.

The kidneys convert a precursor of which vitamin into its active form, calcitriol?

Vitamin D: the kidneys turn it into calcitriol, which helps the body absorb calcium, so when the kidneys fail the bones can grow weak.

Which hormone, secreted mainly by the kidneys, stimulates red blood cell production in the bone marrow?

Erythropoietin, or EPO: because more red cells carry more oxygen, the synthetic copy made to treat anaemia became a banned performance booster for endurance athletes.

The prefix nephro-, as in nephrologist, comes from the word for kidney in which ancient language?

Greek nephros, kidney, gave medicine the prefix, while Latin supplied the adjective, which is why nephrologists treat what is called renal disease.

The kidneys sit in which space of the body?

Retroperitoneal: the kidneys lie behind the lining of the abdomen, against the back wall, so kidney pain is often felt in the back or sides and mistaken for ordinary back pain.

Which pair of ribs partially protects the upper parts of the kidneys?

11th and 12th: these lowest pairs are the floating ribs, attached only to the spine, so they shield just the top of each kidney and leave the rest to back muscle and fat.

The loop of Henle is named after an anatomist of which nationality?

German: Friedrich Gustav Jakob Henle, who found the loop, also argued in 1840 that living organisms spread disease, an idea his student Robert Koch went on to prove.

Which pop star received a kidney from her friend, the actress Francia Raisa, in 2017?

Selena Gomez needed the transplant because lupus had damaged her kidneys, and she kept the summer surgery private until she shared it on Instagram that September.

The cup-shaped structure that surrounds the glomerulus is named after which anatomist?

Bowman: Sir William Bowman identified the capsule when he was just 25, then made his name not in kidney medicine but as one of London's leading eye surgeons.

The specialised cells whose foot processes form part of the glomerular filter are called what?

Podocytes: their interlocking feet leave slits just narrow enough to hold proteins back, so when the cells are damaged, protein spills into the urine.

Which enzyme do the kidneys release into the blood when blood pressure drops too low?

Renin: it starts a chain reaction that narrows blood vessels and makes the body hold on to salt and water, pushing the pressure back up.

ACE, which converts angiotensin I to II, is found predominantly on blood-vessel cells of which organ?

Lungs: the enzyme lines their tiny blood vessels, so the hormone is switched on as blood passes through, and blocking that step is how ACE inhibitor drugs bring blood pressure down.

The adrenal glands, which make cortisol, are also known by which name?

Suprarenal is built from the Latin for above the kidney, just as adrenal means near the kidney, which is how the hormone these glands make came to be called adrenaline.

The pigment that gives urine its usual pale yellow colour is called what?

Urobilin is what is left when the body recycles old red blood cells, and the gut-bacteria enzyme that starts making it was only identified in 2024.

Which Roman emperor is credited with the saying 'money does not smell' after taxing the urine trade?

Vespasian is said to have held a coin from the tax under his son Titus's nose to make the point, and public urinals in France are still called vespasiennes after him.

Which is the most common type of kidney stone?

Calcium oxalate: yet cutting calcium out of the diet does not help, and low-calcium diets are in fact linked to a higher risk of forming these stones.

Which London diarist held a yearly feast to celebrate surviving the removal of a bladder stone in 1658?

Samuel Pepys had the stone cut out in a bedroom at his cousin's house, and his diary records his vow to keep the date as a festival for as long as he lived.

Large branching kidney stones that fill the renal calyces are named after which animal's antlers?

Stag: staghorn stones branch through the kidney like antlers, and most are made of struvite, a mineral that forms only when certain bacteria infect the urinary tract.

ESWL, a non-invasive treatment that breaks up kidney stones from outside the body, uses what?

Shock waves focused from outside the body shatter the stone into pieces small enough to pass out in the urine, which is why lithotripsy means stone crushing.

Which habit is the most important step in preventing kidney stones?

Drinking more water keeps the urine dilute, so stone-forming minerals are flushed away before they can clump into crystals, which is why kidney specialists put it first.

Who built the first working dialysis machine, in the Nazi-occupied Netherlands during World War II?

Willem Kolff went on to build other artificial organs, leading the Utah team whose artificial heart kept Barney Clark alive for 112 days in 1982.

With materials scarce in the occupied Netherlands, the first working dialysis machine relied on which everyday item?

Sausage casings made of cellophane did the filtering: toxins passed out of the blood through the thin membrane into a rinsing fluid on the other side.

Belding Scribner opened the world's first outpatient dialysis centre in 1962 in which Pacific Northwest city?

Seattle: the centre could take only a fraction of those who applied, so a committee that included ordinary citizens chose who got a place, a dilemma often called the start of bioethics.

Belding Scribner's 1960 arm shunt, which first made long-term dialysis possible, was made of which material?

Teflon: blood clots slip off its non-stick surface, so the tubes could stay in a patient's arm and be reconnected to the machine for every session.

The first successful kidney transplant, in Boston in 1954, was performed between what kind of pair?

Identical twins: Ronald Herrick gave a kidney to his brother Richard, whose body accepted it because they shared the same genes, years before anti-rejection drugs existed.

Which honour went in 1990 to Joseph Murray, the surgeon who led the first successful kidney transplant?

Nobel Prize: Murray was a plastic surgeon whose interest began with burned soldiers in World War II, when he wondered why their bodies rejected skin grafted from other people.

Yuriy Voronyi attempted the first human kidney transplant in 1933, stitching the organ into a thigh, in which modern country?

Ukraine: Voronyi operated in the city of Kherson with a kidney taken from a man six hours after death, but it was rejected at once and the patient died two days later.

In a typical kidney transplant, what happens to the recipient's own failing kidneys?

They are left in place, because taking them out adds surgical risk, and the new kidney goes lower down in the front of the abdomen, so most recipients end up with three.

Which vegetable is famous for giving urine a strong smell soon after it is eaten?

Asparagus: digestion turns its asparagusic acid into pungent sulphur compounds, yet in one study of nearly 7,000 people about six in ten said they did not notice the smell.

As of 2023, which was the only country with a legal, government-regulated system of paying living kidney donors?

Iran: under a programme begun in 1988, an unrelated donor receives a payment from the government as well as a sum agreed with the patient who gets the kidney.

In 2019 which country had the highest organ-donor rate in the world?

Spain: its lead is credited less to its opt-out law than to trained transplant coordination teams inside hospitals, who are alerted early to every possible donor.

In 2024 Richard Slayman became the first living person to receive a gene-edited kidney from which animal?

Pig: the donor animal carried 69 gene edits to make its kidney more compatible with humans, and Slayman turned to it after an earlier human kidney transplant had failed.

Doctors usually check how well the kidneys are working with a blood test for which waste product of the muscles?

Creatinine: healthy kidneys clear it steadily, so its level in the blood climbs as they weaken, and labs use that number to estimate how much filtering power is left.

In 1964 surgeon Keith Reemtsma kept a patient alive for nine months with a kidney from which animal?

Chimpanzee: with no long-term dialysis to fall back on, Reemtsma turned to our closest relatives, and this patient recovered well enough to go back to work.

Which future US president lost his wife to Bright's disease and his mother to typhoid on the same day in 1884?

Theodore Roosevelt drew a large X in his diary that day and wrote that the light had gone out of his life; Bright's disease was the old name for kidney inflammation.

The first International Congress of Nephrology met in 1960 in Geneva and which French spa town on the same lake?

Evian: the meeting, which opened in Geneva, founded the International Society of Nephrology with the French doctor Jean Hamburger as its first president.

People with failing kidneys are often told to limit orange juice and tomatoes because of which mineral?

Potassium: damaged kidneys struggle to clear it from the blood, and too much of it can cause dangerous heart and muscle problems.

The two most common causes of chronic kidney disease are high blood pressure and what?

Diabetes: over the years, high blood sugar damages the tiny blood vessels and filters in the kidneys until they can no longer clean the blood properly.

About one in how many people worldwide is thought to be living with chronic kidney disease?

One in 10, yet most of them do not know it, because the disease usually causes no symptoms until the kidneys are badly damaged.

In about 1 in 500 people the two kidneys are fused at the base into one organ named after which object?

A horseshoe: the joined kidney gets stuck lower in the body than usual, yet many people who have one never notice and find out only by chance from a scan.

Which large land mammals share the unusual kidneys of seals and whales, built from clusters of hundreds of mini-kidneys?

Bears: each small lobe works like a complete kidney, though studies find the design lets its owners concentrate their urine no better than an ordinary kidney would.

In the King James Bible and Shakespeare, kidneys are referred to by which old word?

Reins: early English Bibles used the word where the kidneys stand for a person's inner feelings, which God is said to examine, and modern versions usually say mind or soul instead.

Per Jane Grigson, the first published recipe for steak and kidney pudding appeared in 1859 in whose book?

Mrs Beeton printed it as a recipe sent in by a Sussex lady, noting that the county was famous for its savoury puddings, which suggests the dish began as a local speciality.

Which kitchen step destroys the natural toxin in raw red kidney beans that can cause severe vomiting?

Boiling: a hard boil breaks the toxin down, but the gentle heat of a slow cooker may not, so beans stewed from raw can still make people ill within hours.

Which popular Easter flower can cause fatal kidney failure in a cat that merely licks its pollen?

Lily leaves, petals and pollen all damage the tubes of a cat's kidneys, so a cat that grooms pollen off its coat needs a vet urgently.

A 2016 study found that riding which Walt Disney World roller coaster can shake loose small kidney stones?

Big Thunder Mountain shook stones out of a model kidney on about two rides in three from a rear seat, but only one in six up front. A doctor ran the test after patients said the ride had worked for them.

Which fruit, safe for people fresh or dried, can cause sudden kidney failure when eaten by dogs?

Grapes and raisins can leave a dog unable to produce urine within two days, and tartaric acid is the suspected culprit.

Which element did the alchemist Hennig Brand discover in 1669 while heating urine residue in search of gold?

Phosphorus dripped from Brand's red-hot retort and burst into flame. He kept the discovery secret and tried, without success, to turn it into gold.

In Friends, which character passes kidney stones in hospital while Phoebe is giving birth to triplets?

Joey lands in a hospital room of his own in the sitcom's 100th episode. The writers wanted a subplot that ran parallel to Phoebe's labour, so he "gives birth" at the same moment she does.

Which sweet-tasting car fluid can cause fatal kidney failure in cats and dogs that lap up a spill?

Antifreeze usually contains ethylene glycol, which the body turns into acids that wreck the kidneys within one to three days. Less toxic versions swap in propylene glycol.

Which American founding father designed a flexible urinary catheter in 1752 to ease his brother's bladder stones?

Benjamin Franklin had a tube of hinged metal segments made for his brother John, then modestly credited an inventor of 1720 with getting there first.

Which root vegetable can harmlessly turn urine pink or red in about one person in eight?

Beetroot pigments called betalains pass through some people unchanged, a harmless effect known as beeturia. It shows up more often in people who are short of iron.

The oath named after which physician has doctors swear never to cut patients for stone?

Hippocrates lends his name to an oath that bars the knife even for bladder stones, a sign that stone-cutting was already a separate trade. Specialist lithotomists did that risky work.

Alcohol makes drinkers urinate more by suppressing which hormone that tells the kidneys to hold on to water?

Vasopressin is released from the pituitary gland at the base of the brain, and alcohol blocks that release. With less of it around, the kidneys let more water go.

From about the fourth month of pregnancy, a fetus's own urine becomes a major part of what?

Amniotic fluid late in pregnancy is largely the baby's own urine, swallowed and recycled again and again. Too little of it can therefore point to a kidney problem.

Which North American desert rodent has kidneys so efficient that it never needs to drink at all?

Kangaroo rat kidneys make very concentrated urine, and the animal gets all the moisture it needs from chemically breaking down the dry seeds it eats.

Which Motown legend told a London Hyde Park crowd in 2019 that he was about to have a kidney transplant?

Stevie Wonder made the announcement from the stage in July, and the operation was carried out successfully that December.

Which Modern Family actress received a kidney from her father in 2012 and another from her brother in 2017?

Sarah Hyland was diagnosed with kidney dysplasia as a child. Her first transplant failed after a few years, so her younger brother Ian donated the second.

Which comedian and sitcom star received a kidney from his wife Ann in 2005?

George Lopez has a genetic condition that made his kidneys deteriorate. The couple's divorce was finalised in 2011, six years after the transplant.

Which Miami Heat center won the 2006 NBA title less than three years after a kidney transplant?

Alonzo Mourning received the kidney from a cousin he had not seen in 25 years. He came off the bench in the title-clinching game and led the team with five blocks.

Which platinum-blonde MGM star died of kidney failure at 26 while filming Saratoga in 1937?

Jean Harlow was first diagnosed with an inflamed gallbladder before a second doctor saw the real problem. MGM finished the film with body doubles, and it became one of 1937's biggest hits.

Which James Joyce novel introduces Leopold Bloom as he walks to the butcher to buy a breakfast kidney?

Ulysses brings Bloom on stage in its fourth episode, where he carries the cooked breakfast and the morning's letters up to his wife Molly, still lounging in bed.

Which industrial chemical, added to Chinese infant formula in 2008, gave thousands of babies kidney stones?

Melamine is rich in nitrogen, so adding it to watered-down milk fooled quality tests into reading a higher protein content. Some 300,000 children were affected.

Which American poet's death in 1886 was put down by the attending physician to Bright's disease?

Emily Dickinson's physician used the Victorian catch-all for kidney inflammation and recorded that the illness had lasted two and a half years.

Which outer layer of the kidney shares its name with the wrinkled outer layer of the brain?

Cortex is Latin for bark or rind, a fitting name for the layer wrapped around the kidney's inner medulla. The adrenal glands and the ovaries each have one as well.

The striped sections of the kidney's medulla, each ending in a tip called a papilla, are known as the renal what?

Pyramids in the kidney look striped because they are packed with straight, parallel tubes. Each tip drips finished urine into a cup that leads out of the organ.

Which funnel in the middle of the kidney takes its name from the Latin word for a basin?

The renal pelvis gathers urine from the kidney's cup-like chambers and funnels it onward, much as a wash basin feeds a drain pipe. The bony pelvis is named for the same shape.

What is the name of the notch on the kidney's inner curve where the renal artery enters and the vein leaves?

The hilum is the doorway for the kidney's blood vessels, nerves and urine outlet. The spleen and every lymph node have a hilum of their own.

Which major vessel running down the back of the abdomen gives off the two arteries that supply the kidneys?

The aorta gives each kidney a renal artery of its own, branching off directly. Once cleaned, the blood drains back through the renal veins into the vena cava.

Which hormone, made by the adrenal glands, makes the kidneys keep sodium and so pushes blood pressure up?

Aldosterone makes the kidneys retain sodium, and water follows the salt, swelling the volume of blood. The blood-pressure drug spironolactone works by blocking it.

Which sugar do healthy kidneys filter out of the blood and then reabsorb completely, leaving none in the urine?

Glucose is reclaimed in the first stretch of the kidney tubule, which can only carry so much at once. Above that limit, the extra sugar spills into the urine.

Which term, coined by physiologist Walter Cannon, describes the steady internal balance that the kidneys help maintain?

Homeostasis builds on Claude Bernard's idea of a constant internal environment. The kidneys' share of the job is holding the body's fluids, salts and acidity within narrow limits.

Which class of drugs, banned in sport as masking agents, makes the kidneys produce more urine?

Diuretics are abused by boxers and wrestlers to shed fluid before a weigh-in. Their everyday medical job is bringing down high blood pressure.

Which bodily waste product did Friedrich Wöhler make from inorganic chemicals in 1828, a milestone for chemistry?

Urea had only ever come from living bodies, so Wöhler wrote to a colleague boasting that he could now make it without needing a kidney, human or canine.

Uric acid the kidneys fail to clear can crystallise in joints, causing which so-called disease of kings?

Gout earned its royal nickname from its link with rich food and drink. Nine times in ten, though, raised uric acid comes down to kidneys that excrete too little of it.

Which dog breed lacks a working gene needed to break down uric acid, leaving it unusually prone to urinary stones?

Dalmatian breeders crossed the dogs with a Pointer to bring the normal gene back, and some breed clubs objected when the descendants were registered as pedigrees.

Under a 1972 law, which US government programme pays for dialysis for most kidney failure patients of any age?

Medicare was designed for the over-65s, but the 1972 law opened it to people of any age whose kidneys had failed, provided they or a family member had paid in through work.

Which of these contains a nerve toxin that healthy kidneys filter out but that can kill people on dialysis?

Star fruit carries caramboxin, which builds up in the blood when the kidneys cannot clear it. Drinking the juice has left kidney patients severely ill and, in a few cases, dead.

Which chess champion died of kidney failure in Reykjavik in 2008?

Bobby Fischer had a blocked urinary tract but turned down both surgery and medication. He died in the city where he had won the world title 36 years earlier.

Which American magazine's 1962 report on a lay panel choosing who received dialysis helped found bioethics?

Life dubbed the anonymous lay panel the Life or Death Committee. Machines were so scarce that doctors screened patients first and the panel then chose who would be treated.

Nephrologists treat kidney disease with drugs, but which surgical specialist removes kidney stones and bladder tumours?

A urologist is trained as a surgeon and deals with the whole urinary tract, from the kidneys down. The specialty also covers the male reproductive organs.

Which gut bacterium, better known for food-poisoning outbreaks, causes roughly three-quarters of kidney infections?

E. coli usually begins as a bladder infection and climbs up to the kidney, which is why a neglected bout of cystitis can end in fever and flank pain.

Which B vitamin, taken in excess, is flushed out by the kidneys and turns urine a harmless bright yellow?

Riboflavin cannot be stored, so the kidneys get rid of whatever the body does not need. The second half of its name comes from flavus, the Latin for yellow.

Tea-coloured urine after a crush injury or extreme exercise warns of which kidney-threatening muscle condition?

Rhabdomyolysis releases myoglobin from damaged muscle, which darkens the urine. Doctors learned how it harms the kidneys by studying people dug out of collapsed buildings in the London Blitz.

Which Italian microscopist gave his name to both the kidney's filtering corpuscles and the waste tubules of insects?

Marcello Malpighi was also the first to see capillaries, in 1661, which completed the picture of how blood passes from arteries to veins.

Ciclosporin, which stops kidney transplants being rejected, comes from a soil fungus first collected in which country?

Norway supplied the soil sample in 1969, which was taken to Switzerland, where the fungus was isolated. In the wild, the same fungus lives as a parasite on scarab beetles.

Variants of the APOL1 gene that raise the risk of kidney failure evolved as protection against which African disease?

Sleeping sickness parasites are killed by the APOL1 protein in the blood, so the variants spread as a defence in Africa, at a cost to their carriers' kidneys.

Blood enters the capillary tuft of each glomerulus through a single vessel known as which arteriole?

Afferent arterioles bring blood in and efferent ones take it out again. Narrowing or widening the pair is how the kidney fine-tunes its own filtering pressure.

Which group of cells in the kidney's distal tubule senses salt and helps adjust the filtration rate?

Macula densa cells sit where the tubule loops back to touch its own glomerulus. When the passing fluid turns less salty, they signal the incoming arteriole to widen, restoring the filtering pressure.

Nephroblastoma, the most common kidney cancer of childhood, is better known by which surgeon's name?

Wilms tumour is most often found at three or four years old, and about 90% of the children treated for it are cured.

Which French Renaissance writer toured the spas of Europe in 1580 seeking a cure for his kidney stones?

Montaigne inherited the complaint from his father's family and kept a travel journal of the springs he tried, settling for a while at Bagni di Lucca in Italy.

ACE inhibitors, blood-pressure drugs that also protect the kidneys, were developed from the venom of which animal?

Pit viper venom from Brazil's jararaca makes a victim's blood pressure collapse. A Brazilian scientist took a sample to London, and captopril, the first of the drugs, was made in 1975.

Which Diff'rent Strokes child star's growth was stunted by a kidney disease that led to two transplants?

Gary Coleman stopped growing at 4 ft 8 in because of the disease and the steroids used to treat it. Both of his transplants, in 1973 and 1984, failed, leaving him on dialysis.

Which mammal's kidneys start passing urine within two minutes of a meal, lightening it enough to fly off?

A vampire bat can drink about half its body weight in blood, so its gut rushes the water to the kidneys. It then launches by crouching and flinging itself into the air.