Kidneys Trivia
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99 free Kidneys trivia questions with answers — science & nature quiz, new questions added Oct 2026.
The kidneys are two bean-shaped organs about the size of a fist, and they do far more than make urine. This quiz covers the whole story: where they sit and how they are protected, the million nephrons packed into each one, the loop of Henle and why a camel's is longer than yours, the 180 litres of filtrate a day, and the hormones the kidneys make that control blood pressure, red blood cells and vitamin D. From there it moves into medicine and history: Willem Kolff building the first dialysis machine from sausage casings and juice cans in occupied Holland, the 1954 Herrick twin transplant that won Joseph Murray a Nobel Prize, Richard Bright's disease, kidney stones dated to 4,800 BC, the 2024 pig-kidney xenotransplants, and the one country where selling a kidney is legal. There is also room for the lighter side, from Roman urine taxes and steak and kidney pie to why ancient Egyptians left the kidneys inside their mummies. Easy questions suit anyone who remembers school biology; the expert tier is for nurses, medics and pub-quiz specialists. Every answer was checked against Wikipedia's articles on the kidney, nephron, dialysis, transplantation and related topics, and the supporting sentence is attached to each question.
30 of 99 questions with answers and explanations. Play the quiz
Q 01An adult human kidney is about the size of which of these?
A fist
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.
Q 02Which tube carries urine from each kidney to the bladder?
Ureter
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.
Q 03Which organ's bulk pushes the right kidney slightly lower than the left?
Liver
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.
Q 04Approximately how many nephrons does each adult human kidney contain?
1 million
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.
Q 05About what share of the blood pumped by the heart flows through the kidneys?
About 20%
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.
Q 06Most of the roughly 180 litres the kidneys filter each day ends up where?
Back in the blood
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.
Q 07The kidneys convert a precursor of which vitamin into its active form, calcitriol?
D
Vitamin D: the kidneys turn it into calcitriol, which helps the body absorb calcium, so when the kidneys fail the bones can grow weak.
Q 08Which hormone, secreted mainly by the kidneys, stimulates red blood cell production in the bone marrow?
Erythropoietin
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.
Q 09The prefix nephro-, as in nephrologist, comes from the word for kidney in which ancient language?
Greek
Greek nephros, kidney, gave medicine the prefix, while Latin supplied the adjective, which is why nephrologists treat what is called renal disease.
Q 10The kidneys sit in which space of the body?
Retroperitoneal
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.
Q 11Which pair of ribs partially protects the upper parts of the kidneys?
11th and 12th
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.
Q 12The loop of Henle is named after an anatomist of which nationality?
German
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.
Q 13Which pop star received a kidney from her friend, the actress Francia Raisa, in 2017?
Selena Gomez
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.
Q 21Which is the most common type of kidney stone?
Calcium oxalate
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.
Q 22Which London diarist held a yearly feast to celebrate surviving the removal of a bladder stone in 1658?
Samuel Pepys
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.
Q 23Large branching kidney stones that fill the renal calyces are named after which animal's antlers?
Stag
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.
Q 14The cup-shaped structure that surrounds the glomerulus is named after which anatomist?
Bowman
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.
Q 15The specialised cells whose foot processes form part of the glomerular filter are called what?
Podocytes
Podocytes: their interlocking feet leave slits just narrow enough to hold proteins back, so when the cells are damaged, protein spills into the urine.
Q 16Which enzyme do the kidneys release into the blood when blood pressure drops too low?
Renin
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.
Q 17ACE, which converts angiotensin I to II, is found predominantly on blood-vessel cells of which organ?
Lungs
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.
Q 18The adrenal glands, which make cortisol, are also known by which name?
Suprarenal
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.
Q 19The pigment that gives urine its usual pale yellow colour is called what?
Urobilin
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.
Q 20Which Roman emperor is credited with the saying 'money does not smell' after taxing the urine trade?
Vespasian
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.
Q 24ESWL, a non-invasive treatment that breaks up kidney stones from outside the body, uses what?
Shock waves
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.
Q 25Which habit is the most important step in preventing kidney stones?
Drinking more water
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.
Q 26Who built the first working dialysis machine, in the Nazi-occupied Netherlands during World War II?
Willem Kolff
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.
Q 27With materials scarce in the occupied Netherlands, the first working dialysis machine relied on which everyday item?
Sausage casings
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.
Q 28Belding Scribner opened the world's first outpatient dialysis centre in 1962 in which Pacific Northwest city?
Seattle
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.
Q 29Belding Scribner's 1960 arm shunt, which first made long-term dialysis possible, was made of which material?
Teflon
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.
Q 30The first successful kidney transplant, in Boston in 1954, was performed between what kind of pair?
Identical twins
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.