50 Fun Facts About Kidneys

Roughly how long is an adult human kidney?

About the length of a smartphone; a Danish study measured a median of 11.2 cm on the left and 10.9 cm on the right.

Which tube carries urine from each kidney to the bladder?

The urethra is the exit tube from the bladder; the two ureters feed it from above.

What is the structural and functional unit of the kidney called?

Each adult human kidney has around a million of them; a mouse kidney gets by with about 12,500.

Approximately how many nephrons does each adult human kidney contain?

By early chronic kidney disease that number is roughly halved, similar to the loss between young adulthood and one's seventies.

What share of the heart's output flows through the kidneys in an adult?

That is a huge share for two organs weighing a few hundred grams between them, which is why blood-pressure problems hit the kidneys hard.

About how much filtrate do an adult's kidneys produce each day, most of it reabsorbed?

Only around one to two litres leaves the body as urine; the rest is reclaimed along the tubules.

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

Calcitriol boosts calcium absorption in the gut, which is one reason kidney failure leads to bone disease.

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

Its synthetic form became notorious as a doping product in cycling; the Festina affair exposed it before a test even existed.

The prefix nephro- comes from the word for kidney in which language?

The adjective renal comes from the Latin renes instead, which is why kidney doctors are nephrologists who treat renal disease.

The kidneys sit in which space of the body?

They lie behind the peritoneal lining of the abdomen, high up on either side of the spine at a slight angle.

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

The right kidney sits slightly lower than the left because the liver takes up room above it.

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

Friedrich Gustav Jakob Henle's loop builds the salty gradient in the kidney medulla that lets urine be concentrated.

Which animal's loop of Henle, twice a human's length, concentrates urine to about 2,800 mOsm?

An Australian hopping mouse goes further still, with a 5.2 mm loop that makes its medulla about 9,000 mOsm.

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

Bowman's space collects the filtrate; normally only blood proteins, blood cells and platelets are held back.

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

The name comes from the Greek for foot; the interlocking foot processes leave slits just narrow enough to keep proteins in the blood.

Which cells in the kidney release the enzyme renin when blood flow to the organ drops?

Renin kicks off the renin-angiotensin system, the blood-pressure cascade targeted by ACE inhibitors.

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

The kidney starts the cascade with renin, the liver supplies angiotensinogen, and the lungs finish the job.

The glands atop the kidneys that produce adrenaline and cortisol are also called what?

The name, coined by Jean Riolan the Younger in 1629, is Latin for above the kidney.

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

It is a final waste product of breaking down the heme in old red blood cells.

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

His name still survives in the words for public urinals in France, Italy and Romania.

Which is the most common type of kidney stone?

Oxalate is about 15 times stronger than calcium at promoting these crystals, which is why spinach and rhubarb get a bad name.

A kidney stone found in an ancient Egyptian mummy of a teenage boy was dated to roughly when?

Surgery to remove stones was described by Sushruta in India around 600 BC, and the Hippocratic Oath tells physicians to leave cutting for stones to specialists.

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

These staghorn stones are nearly always struvite and only form in the presence of urease-producing bacteria.

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

The full name is extracorporeal shock wave lithotripsy; lithotripsy literally means stone crushing.

In the developed world, roughly what is the lifetime risk of getting a kidney stone?

In the Middle East it can reach 20-25%, and about half of sufferers get another one within ten years.

Who built the first working dialysis machine, in the occupied Netherlands in 1943?

He later moved to Utah, where his lab produced the Jarvik artificial heart implanted in Barney Clark in 1982.

Kolff's first prototype dialyzer was built from orange juice cans, auto parts and what else?

The casings served as the semi-permeable membrane; his first patient to be saved was a 67-year-old woman in 1945.

The world's first outpatient dialysis facility, opened by Belding Scribner in 1962, was in which US city?

Scribner's Teflon shunt made repeated dialysis possible; the centre was later renamed the Northwest Kidney Centers.

Dialysis is usually started once roughly how much kidney function has been lost?

That corresponds to a glomerular filtration rate below 15; life expectancy on dialysis is typically 5-10 years, though some live 30.

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

Ronald Herrick gave a kidney to his brother Richard; sharing the same genes sidestepped rejection years before immunosuppressants existed.

Which surgeon led the 1954 Herrick kidney transplant and won the 1990 Nobel Prize in Medicine?

The operation in Peter Bent Brigham Hospital's Operating Room 2 lasted five and a half hours.

In the first human kidney transplant attempt in 1933, Yuriy Voronyi implanted the organ into which part of the body?

The kidney came from a deceased donor and had been removed six hours earlier; the patient died two days later of blood-group rejection.

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

The new kidney is usually placed lower down in the iliac fossa and plumbed into the iliac vessels instead.

In 2009 Chris Strouth got a kidney from a donor he had met on which platform, believed to be a first?

Kidney swap chains have since grown enormous; a 2014 chain involved 70 participants.

Which is the only country with a legal, working payment system for kidney donation?

The system began in 1988 and had eliminated the kidney shortage by 1999; middlemen and surgeons are forbidden from taking payment.

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

Spain's opt-out system reached 46.91 donors per million people, ahead of the US at 36.88.

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

The surgery was at Massachusetts General Hospital; a 2025 recipient, Tim Andrews, lived with such a kidney for 271 days.

Which surgeon led the first pig-kidney xenotransplant into a brain-dead patient in 2021?

The team also transplanted the pig's thymus, which helped avoid immediate rejection.

The 1964 record for a xenotransplant, 273 days, was set with a kidney from which animal?

Tim Andrews's 2025 pig kidney fell just two days short of that record.

Bright's disease, the old name for kidney inflammation, honours a physician of what nationality?

Richard Bright described it in 1827; the diagnostic triad was dropsy, albumin in the urine and diseased kidneys at autopsy.

The word nephrology was first used at a 1960 congress held in Geneva and which French spa town?

The French term had been proposed by Jean Hamburger in 1953; that meeting founded the International Society of Nephrology.

World Kidney Day is observed each year on the second Thursday of which month?

It is a joint campaign of the International Society of Nephrology and the International Federation of Kidney Foundations.

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

About one in three adults with diabetes has chronic kidney disease, compared with one in five with hypertension.

About how many people worldwide were estimated to have chronic kidney disease in 2016?

The condition killed about 1.2 million people in 2015, roughly triple the toll of 1990.

A horseshoe kidney, where the two kidneys are fused, occurs in roughly one in how many live births?

Duplex kidneys are commoner still, at around 1% of people, and most never know they have them.

Which marine mammals are exceptions to the classic bean shape, having multi-lobed reniculate kidneys?

Pinnipeds and cetaceans have kidneys made of many small lobules, thought to help handle salt water and diving.

In ancient Egyptian mummification, which two organs were typically left inside the body?

Egyptian drawings pair the heart and two kidneys as a set of scales, hinting they were tied to judgement.

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

The word comes from the Latin renes, and several verses say God searches the reins and the heart.

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

Beeton made it a pudding rather than a pie and suggested enriching it with mushrooms or oysters.

Raw kidney beans are toxic unless boiled because they contain high levels of which compound?

As few as five raw beans can cause severe vomiting, and slow cookers running at 80 C do not get hot enough to destroy it.