100 Fun Facts About Urinary System

Which four organs make up the human urinary system?

Kidneys, ureters, bladder, urethra: the kidneys make urine, the paired ureters carry it down, the bladder stores it, and the single urethra empties it; male and female tracts differ mainly in urethral length.

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

Nephron: the kidney's working unit, a filtering corpuscle feeding a long tubule that reabsorbs water and solutes, so the blood filtrate that enters it leaves as urine.

Roughly how many nephrons does each adult human kidney contain?

About 1 million nephrons per kidney is the textbook figure, though counts vary widely between individuals; new nephrons stop forming before birth, and the number declines slowly with age.

The tuft of filtering capillaries at the start of each kidney filtration unit is called what?

Glomerulus: the knot of capillaries inside each renal corpuscle, fed by an afferent arteriole and drained by a narrower efferent one, whose resistance keeps the filtration pressure high.

The cup-shaped structure that surrounds the kidney's filtering capillary tuft is named after which anatomist?

Bowman's capsule, described by English surgeon William Bowman in 1842, is the cup around the capillary tuft; its inner layer is made of podocytes whose interlocking 'feet' form part of the filtration barrier.

Which U-shaped section of the kidney tubule dips down into the renal medulla?

Loop of Henle: the hairpin that descends into the medulla and climbs back; its countercurrent flow builds the salt gradient that lets mammals make urine more concentrated than blood.

The glomerular filtration rate of a healthy adult amounts to roughly how much filtrate per day?

180 litres a day follows from a normal glomerular filtration rate of about 125 millilitres per minute; nearly all of that filtrate is reabsorbed along the tubule, so only a tiny fraction leaves as urine.

What share of the heart's output goes to the kidneys in a healthy adult?

About 20-25% of cardiac output, roughly 1.2 litres of blood a minute, flows through the kidneys, far more than their size alone would demand, because filtration needs high flow.

The renal arteries branch directly from which major vessel?

Abdominal aorta: the renal arteries leave it at about the level of the first or second lumbar vertebra and enter each kidney at the hilum, while the renal veins return blood to the inferior vena cava.

Which kidney usually sits slightly lower in the body, and why?

The right, because of the liver: the liver's large right lobe sits directly above the right kidney and nudges it lower than the left, and both kidneys slide down a little with each inhalation.

About how long is an adult human kidney?

12 cm is the textbook length of an adult kidney, roughly the size of a fist; ultrasound surveys put the median nearer 11 cm, with the left kidney slightly longer and larger than the right.

What gland sits on top of each kidney?

Adrenal glands cap each kidney inside the same fatty fascia; the outer cortex makes steroid hormones such as cortisol, while the inner medulla releases adrenaline.

Which kidney hormone, released in response to low oxygen, stimulates red blood cell production?

Erythropoietin is made mainly by fibroblast-like cells in the kidney cortex when oxygen runs low; its synthetic form treats the anaemia of chronic kidney disease and became notorious as a doping agent in endurance sport.

The kidneys convert a precursor into the active form of which vitamin?

Vitamin D is activated in the kidney, where 25-hydroxyvitamin D is converted to calcitriol by the enzyme 1-alpha-hydroxylase; advanced kidney disease therefore often brings bone problems.

Which kidney enzyme is the first messenger in the cascade ending with angiotensin II raising blood pressure?

Renin, secreted by juxtaglomerular cells when renal perfusion falls, cleaves angiotensinogen to angiotensin I, which ACE then converts to angiotensin II; ACE inhibitors and ARBs act on this cascade rather than on the heart.

Antidiuretic hormone (vasopressin) is released from which part of the brain?

Posterior pituitary: vasopressin is made in the hypothalamus but stored in and released from this lobe; it makes the collecting ducts insert aquaporin channels and retain water, and alcohol suppresses it, hence beer's trips to the bathroom.

Severe diabetes insipidus can push daily urine output to roughly what volume?

Nearly 20 litres a day is possible in severe cases, more than ten times normal output; central diabetes insipidus is a shortage of vasopressin, the nephrogenic form is kidneys that ignore it, and blood sugar plays no part.

Which hormone acts on the distal tubules to increase sodium reabsorption, raising blood pressure?

Aldosterone, made in the outer cortex of the gland capping each kidney, drives sodium (and water) reabsorption in the distal tubule and collecting duct in exchange for potassium, raising blood volume and pressure.

How long are the adult human ureters, the tubes carrying urine from kidney to bladder?

20-30 cm long and only about 3-4 mm wide, each ureter runs down behind the abdominal lining and enters the bladder obliquely, a slant that helps stop urine flowing back up.

What is the name of the wave-like muscular contraction that moves urine down the ureters?

Peristalsis: rings of smooth muscle in the ureter wall contract in sequence, squirting urine into the bladder in periodic spurts, so flow continues even when you are lying flat.

The typical adult bladder comfortably holds how much urine before urination?

300-500 ml is the comfortable working capacity of an adult bladder, whose wall folds (rugae) flatten as it fills; under pressure it can stretch to hold considerably more.

What is the name of the smooth muscle in the bladder wall that contracts to expel urine?

Detrusor: the three-layered smooth muscle of the bladder wall, driven by parasympathetic nerves; it stays relaxed for hours as the bladder fills, then contracts throughout voiding to push urine out.

What is the stretchy urinary-tract lining that flattens as the bladder fills?

Urothelium, also called transitional epithelium, lines the renal pelvis, ureters, bladder and upper urethra; its surface umbrella cells unfold as the bladder fills and carry a glycocalyx that shields them from urine.

The micturition centre that controls urination sits in which part of the brain?

The brainstem houses the pontine micturition centre (Barrington's nucleus), which coordinates bladder contraction with sphincter relaxation; the frontal cortex only decides when to let that reflex run.

Approximately how long is the female urethra?

About 4 cm is the length of the female urethra, a fraction of the male one that runs the length of the penis; that short path is a major reason urinary infections are more common in women.

Which gland below the male bladder acts as a switch between urination and ejaculation?

Prostate: a walnut-sized gland wrapped around the urethra just below the bladder; its muscle closes the bladder outlet during ejaculation, and when it enlarges with age it squeezes the urethra, causing the frequency and dribbling of benign prostatic hyperplasia.

What percentage of urine is water?

91-96% of urine is water; the remainder is dissolved nitrogen waste, sodium, potassium, chloride and other salts, and the proportion of water falls as the kidneys concentrate urine during dehydration.

Which nitrogen waste is the most abundant dissolved solid in human urine?

Urea is made in the liver by the urea cycle, which packages the ammonia released when amino acids are broken down into a far less toxic, water-soluble molecule that the kidneys then excrete.

Which pigment, a breakdown product of haemoglobin, gives urine its yellow colour?

Urobilin (urochrome) forms when gut bacteria break bilirubin down to urobilinogen, some of which is reabsorbed, oxidised and excreted; the more concentrated the urine, the deeper the yellow, a rough hydration gauge.

Eating which vegetable gives some people's urine a distinctive smell from a sulphur compound named after it?

Asparagus contains asparagusic acid, which the body breaks into volatile sulphur compounds such as methanethiol; not everyone produces the odour, and not everyone can smell it, both traits being partly genetic.

Diabetes mellitus got its name from what property of the patient's urine?

It is plentiful and sweet: 'diabetes' is Greek for a siphon, for the copious flow, and 'mellitus' is Latin for honeyed, after the sugary taste of the urine that physicians once diagnosed by tasting.

Which element did Hennig Brand discover in 1669 by distilling fermented urine?

Phosphorus, a waxy solid that glows in the dark, was the residue Brand obtained in Hamburg by boiling down and distilling large quantities of stale urine while searching for the philosopher's stone.

Which Roman emperor said 'money does not smell' when challenged over a tax on urine?

Vespasian, taxing the urine collected from public urinals, answered his son Titus's objection by holding a coin to his nose, the origin of 'pecunia non olet'; fullers used the fermented urine's ammonia to clean and whiten wool.

The most common type of human kidney stone is made of which compound?

Calcium oxalate makes up the large majority of kidney stones, roughly three-quarters; stones under about 5 mm usually pass on their own, while larger ones can lodge in a ureter and cause renal colic.

Surgery to remove kidney stones was described as early as 600 BC by which ancient Indian physician?

Sushruta, author of the Sushruta Samhita, described perineal lithotomy, cutting into the bladder to extract a stone, along with over a hundred surgical instruments; the text is traditionally dated to around the 6th century BC.

Extracorporeal shock wave lithotripsy breaks up kidney stones from outside the body using what?

Focused ultrasonic pulses, in lay terms: a generator outside the body sends acoustic shock waves, aimed with imaging, through the tissue to shatter the stone into passable fragments; the first human treatment was in Munich in 1980.

Which Dutch physician built the first working dialysis machine in 1943 from juice cans and sausage casings?

Willem Kolff built his rotating-drum artificial kidney in occupied Kampen in 1943; his early patients all died, but in 1945 a 67-year-old woman in a uraemic coma woke after 11 hours on the machine, the first patient saved by dialysis.

The first successful kidney transplant, by Joseph Murray in 1954, was between what kind of donor and recipient?

Identical twins Ronald and Richard Herrick were donor and recipient, so the graft faced no immune rejection; Murray shared the 1990 Nobel Prize in Physiology or Medicine for the work.

Which bacterium is by far the most common cause of urinary tract infections?

E. coli, normally a harmless gut resident, causes the large majority of uncomplicated urinary infections after spreading from the bowel to the urethra; about half of all women have at least one UTI in their lifetime.

An infection of the kidney itself, as opposed to the bladder, is called what?

Pyelonephritis usually begins as a bladder infection that ascends the ureters into the renal pelvis and kidney tissue, adding fever, chills and flank pain to the burning of cystitis.

The medical term for blood in the urine is what?

When you can see it, doctors call it 'gross' hematuria; often it is only detectable under a microscope.

Wilms' tumour, a childhood cancer named after a German surgeon, is also known by what name?

Nephroblastoma, the kidney cancer of early childhood, usually appears before age five as a painless abdominal mass; with surgery and chemotherapy roughly nine in ten children are cured.

Which specialist treats diseases of the kidney tissue, as opposed to a urologist who handles the plumbing?

Nephrologist: a physician who manages kidney disease medically, from hypertension and electrolyte disorders to dialysis, while a urologist is a surgeon; 'nephros' is Greek and 'ren' Latin for the kidney.

Land mammals over three kilograms all take roughly how long to empty their bladders?

21 seconds (give or take 13) is the near-constant emptying time found in a 2014 Georgia Tech study; larger animals have longer, wider urethras, so gravity drives faster flow through a bigger bladder.

Healthy adults normally produce how much urine per day?

800-2,000 ml a day is the normal range with ordinary fluid intake; output above about 2.5 litres is called polyuria, below 400 ml oliguria, and below 100 ml anuria.

Roughly what share of the fluid filtered by the kidneys is reabsorbed rather than passed as urine?

99% of the filtrate is reclaimed along the tubules, most of it in the proximal tubule, so the kidneys filter many times the body's total blood volume each day yet pass only a small fraction as urine.

Who reported the first ureteroscopy, an inspection of the ureter from inside, in 1929?

Hampton Young, the Johns Hopkins urologist, passed a rigid cystoscope up a boy's grossly dilated ureter in 1912, a feat he reported in 1929; flexible fibre-optic ureteroscopy followed decades later.

The human kidney's lobes each contain a cone-shaped region of medulla called what?

A renal pyramid is the cone of medullary tissue, striped with collecting ducts, at the core of each lobe; a kidney has roughly 8 to 18 of them, each tip (papilla) draining into a minor calyx.

Which smooth patch of the bladder floor lies between the two ureter openings and the urethra?

The trigone is the smooth triangle on the bladder floor between the two ureteric orifices and the internal urethral opening; unlike the rest of the lining it does not fold, and it is especially sensitive to stretch, signalling fullness.

What is the medical term for bed-wetting in children during sleep?

Nocturnal enuresis is involuntary urination during sleep in a child old enough to be expected to stay dry, usually taken as age five or more; it often runs in families and most children outgrow it.

Which astronaut urinated in his spacesuit while waiting to become the first American in space?

Alan Shepard lay in his capsule for almost three hours of delays before a flight that lasted about 15 minutes. Nobody had fitted a urine collector, so he simply went in the suit.

Which American Founding Father designed a flexible catheter to help his brother's bladder stones?

Benjamin Franklin built the device in 1752 from hinged metal segments, so that it could bend on the way in. He credited an earlier inventor, Francesco Roncelli-Pardino, with the idea.

Urinating on a sting from which sea creature is a popular remedy that can make the pain worse?

Jellyfish tentacles can fire millions of microscopic stinging cells into the skin on contact. Only some species carry venom that causes a bad reaction in humans.

Which sports drink began after a Florida coach asked why his players never urinated during games?

Gatorade grew out of that 1965 question to Dr Robert Cade, whose team tested a salty, sugary drink on the Florida Gators. The players first knew it as Cade's Ade and Cade's Cola.

Which Disney roller coaster did a doctor's study find can shake small kidney stones loose?

Big Thunder Mountain was ridden 20 times by a doctor carrying a model kidney with stones inside. The stones passed about 64% of the time from a rear seat, against 17% at the front.

Which astronomer fell fatally ill after refusing to leave a Prague banquet to relieve himself?

Tycho Brahe thought leaving the table would be a breach of etiquette, by Johannes Kepler's first-hand account. He died eleven days later, in 1601, barely able to urinate.

Which pancake topping names a rare inherited disease that changes how a baby's urine smells?

Maple syrup urine disease leaves the body unable to process three amino acids: leucine, isoleucine and valine. Their build-up scents earwax too, within about 12 hours of birth.

Which root vegetable harmlessly turns urine pink or red in about one in ten people who eat it?

Beetroot colours urine with red betalain pigments, a harmless quirk that doctors call beeturia. It shows up more often and more strongly in people who are short of iron.

Early footballs and rugby balls were made by inflating the bladder of which farm animal?

Pig bladders inside leather covers are why American footballs are still nicknamed pigskins. India rubber began to replace them in the 1860s.

Which ancient physician's oath forbids doctors to 'cut for stone' from a patient's bladder?

Hippocrates described specialist stone-cutters who did the risky operation instead. The line is an early sign of the split between physicians and surgeons.

Which dog breed, the star of a Disney classic, has a gene fault that can cause bladder stones?

Dalmatians lack the working gene that lets other dogs break down the waste product behind gout. Owners are told to limit organ meats and other purine-rich foods.

Which North American desert rodent has kidneys so efficient that it may never need to drink water?

Kangaroo rats get the water they need from breaking down the seeds they eat. They pass very concentrated urine and sit out the day in cool, humid burrows plugged with soil.

Aged urine was once collected to make saltpetre, a key ingredient of which explosive?

Gunpowder makers got saltpetre from heaps of manure and straw that were kept moist with urine for about a year. Small farmers in Switzerland collected it in sandpits under their stables.

Which pungent compound, released as stale urine breaks down, once made it a household cleaner?

Ammonia in the aged liquid cleaned and whitened woollen cloth. Roman fullers stood in tubs laced with it and trampled the cloth underfoot.

Which exercises, named after an American gynaecologist, strengthen the muscles that hold urine in?

Kegels take their name from Arnold Kegel, who described them in 1948. Margaret Morris had published the same idea in 1936 and received little credit for it.

Diuretic drugs such as furosemide, which make the kidneys pass more urine, go by which nickname?

Water pills make the kidneys move extra salt into the urine, and water follows it out. They also help blood vessels widen, another way they bring blood pressure down.

When a patient receives a kidney transplant, what usually happens to the two failed kidneys?

They are left in place unless there is a medical reason to take them out, since removal adds surgical risk. The new kidney usually sits lower down, in the belly.

In the later months of pregnancy, a fetus's own urine makes up much of which protective liquid?

Amniotic fluid gains fetal urine once the kidneys start working, at around week 16, and the fetus swallows it again. Too little of it can point to a kidney problem.

Needle-shaped crystals of which waste product, normally passed in urine, cause the pain of gout?

Uric acid builds up in about nine cases in ten because the kidneys clear too little of it, not because the body makes too much. The same crystals can form kidney stones.

Which sugar do healthy kidneys filter out of the blood and then take back completely?

Glucose spills into urine only when there is more than the kidneys can reabsorb, which is why a urine test can flag diabetes. One class of diabetes drugs blocks that reabsorption on purpose.

Which mineral, popularly linked with bananas, can build up dangerously in the blood when the kidneys fail?

Potassium that failing kidneys cannot clear can disturb the heartbeat and even cause cardiac arrest. Eleven bananas hold roughly a full day's worth of it.

Which English diarist held a yearly feast to celebrate surviving the removal of his bladder stone?

Samuel Pepys had the operation in a cousin's bedroom in 1658, two years before he began the diary. He kept up the anniversary celebration for several years.

At Ypres in 1915, Allied soldiers breathed through urine-soaked cloths to counter which poison gas?

Chlorine is partly neutralised by a compound in urine, a trick passed along the line within days of the first German attack. Both sides then set about developing proper gas masks.

Home pregnancy tests work by detecting which hormone, made by the developing placenta, in urine?

hCG can be released as soon as six days after ovulation and rises quickly, peaking at about eight to ten weeks of pregnancy. A blood test picks it up earlier than a urine one.

Which group of animals has no urinary bladder, passing nitrogen waste as a semi-solid paste instead?

Birds send kidney waste down the ureters straight into the intestine, so it leaves mixed in with the droppings. They have no separate urethral opening either.

Which mammals can spend an entire winter's hibernation without once urinating, eating or drinking?

Bears recycle the waste nitrogen their bodies make into fresh protein, so nothing needs flushing out. With enough stored fat, their muscles stay in good condition until spring.

Sailors visiting the Galápagos once drank water stored in the bladders of which island reptiles?

Giant tortoises can drink large amounts very quickly and store it, which made them living water casks on ships. Charles Darwin found the bladder water of one clear, with only a slightly bitter taste.

Doctors gauge how well the kidneys are working from blood levels of which muscle waste product?

Creatinine is released by muscle at a steady rate and leaves the body unchanged through the kidneys, so a rising level means they are falling behind. Muscular people naturally run higher.

Which slim instrument does a urologist pass up the urethra to look inside the bladder?

Cystoscopes range from the thickness of a pencil up to about 9 mm and carry a light at the tip. Many have extra channels that guide other instruments in to treat a problem on the spot.

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

Riboflavin is a yellow-orange powder in pure form and is even used as a food colouring, E101. The body cannot store a surplus, so the extra is quickly passed out.

Porphyria is named from the Greek word for which colour, the shade urine may turn during an attack?

Purple urine gave the whole group of disorders their name, from the Greek porphyra. A urine test for a chemical called porphobilinogen is still the first step when an attack is suspected.

Before modern chemistry, European dyers dissolved which plant dye in vats of stale urine?

Indigo will not dissolve in water, so the vat first turned it into a yellowish soluble form. Cloth went blue only afterwards, as the dye met the air.

About one person in 500 is born with kidneys fused into a single organ named after which object?

A horseshoe kidney forms in the womb when the two organs fuse. It is more common in men and usually causes no symptoms, so most cases are found by chance.

Doctors call a kidney stone a renal calculus, from the Latin word for which small object?

Pebble counters on Roman counting boards also gave us the calculus of mathematics and the verb calculate. Romans spoke of doing their sums as 'placing pebbles'.

What holds a Foley catheter in place inside the bladder once a nurse has inserted it?

A small balloon at the tip is filled with water once inside, so the tube cannot slip out. The design dates from 1929 and is named after the Boston surgeon Frederic Foley.

Blood filtered by the kidneys drains through the renal veins into which great vessel?

The inferior vena cava runs to the right of the midline, so the left renal vein has to be about three times as long as the right one to reach it.

Which brain region triggers thirst and signals the kidneys to save water when blood gets too salty?

The hypothalamus holds nerve cells that sense how concentrated the blood is. The same small region also governs body temperature, hunger and sleep.

Which organ, when stretched by extra blood, releases a hormone that makes the kidneys shed salt?

The heart makes the hormone in muscle cells of the upper chambers, the atria, which respond to the stretch. Shedding salt takes water with it, so the volume of blood falls.

Researchers have overturned which long-held belief about the urine inside a healthy bladder?

It is sterile was the standard teaching until bacteria were found living even in healthy bladders. The finding opened a new field of study, the urinary microbiome.

Kidney disease was long named after which English physician, who first described the symptoms?

Richard Bright linked swelling, protein in the urine and diseased kidneys in 1827. The label Bright's disease has since been retired, but in its day it was treated with blood-letting, mercury and opium.

Insects clear nitrogen waste through which tubes, named after a seventeenth-century anatomist?

Malpighian tubules draw waste out of the insect's blood and empty it into the gut, where water is taken back. Arachnids, myriapods and tardigrades have them too.

The Hogben pregnancy test of the 1940s and 1950s meant injecting a woman's urine into which animal?

Frogs of an African clawed species produced eggs within 8 to 12 hours if the woman was pregnant. The test was used around the world into the 1960s, with the frogs exported in great numbers.

Surgeons join an artery to a vein in the arm to give dialysis needles a way in, creating what?

A fistula of this kind replaced a Teflon tube that stayed in the patient between sessions and lasted only days to weeks. Its inventor took the idea from injuries he had seen in Korean War veterans.

One form of dialysis uses no blood-filtering machine, relying on which membrane lining the belly?

The peritoneum lets waste products pass out of the blood vessels beneath it into fluid run into the belly through a tube. The fluid is left to dwell there and is then drained away.

What old English name was given to aged urine, once saved for scrubbing floors and washing wool?

Lant was collected from bedpans by the younger servants and left to ferment into a mild caustic before use. In wool towns, the whole community was expected to contribute to the supply.

What is the clinical name for 'shy bladder', the inability to urinate when other people are nearby?

Paruresis is considered a form of social anxiety rather than a physical fault. In severe cases a person can urinate only when alone at home.

The kidneys keep blood from turning too acidic by reclaiming which buffering ion from the filtrate?

Bicarbonate cannot be carried straight out of the filtrate, so tubule cells rebuild it through a chain of reactions. Most of it, 80 to 90%, is recovered early in the tubule.

Dark yellow urine with a strong smell is most often a warning sign of which easily fixed condition?

Dehydration makes the kidneys hold back water, so the same wastes leave in less liquid and look darker. The colour and the number of bathroom trips return to normal once it resolves.

The lungs count as part of the excretory system because they remove which waste gas from the blood?

Carbon dioxide diffuses out of the bloodstream in the lungs as a normal part of breathing. Amphibians also lose theirs straight through their moist, scale-less skin.

Which habit is the biggest known risk factor for bladder cancer, causing about half of all cases?

Smoking sends cancer-causing molecules into the blood, and the kidneys filter them into the urine that the bladder stores. The risk rises with both the daily count and the years of the habit.