98 Fun Facts About Urinary System

Which four organs make up the human urinary system?

Kidneys, ureters, bladder, urethra: the kidneys make urine around the clock, the ureters carry it down, and the bladder stores it so the urethra only has to empty it a few times a day.

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 microscopic filtering units does each adult human kidney contain?

About 1 million filtering units per kidney is the textbook figure; all of them are formed before birth, so the count can only fall 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, unusual in draining into a second arteriole rather than a vein, whose resistance keeps the filtering pressure high.

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

Bowman's capsule, named after the British surgeon Sir William Bowman, is the cup around the capillary tuft; its inner layer is made of podocytes, whose interlocking 'feet' leave the slits through which blood is filtered.

Which part of the kidney tubule sets up the salt gradient that lets the body make concentrated urine?

Loop of Henle: a hairpin that dips into the medulla and climbs back, its two limbs carrying fluid in opposite directions; that countercurrent flow multiplies the salt gradient.

A healthy adult's kidneys filter roughly how much fluid out of the blood each day?

180 litres a day is the textbook figure, from about 125 millilitres every minute; since the body holds only a few litres of blood, the same fluid is filtered many times over each day.

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

About 20% of the heart's output, more than a litre of blood every minute, passes through the kidneys, although the pair together weigh only about 300 grams.

The renal arteries branch directly from which major vessel?

Abdominal aorta: the renal arteries branch straight off it, one to each kidney; a transplanted kidney, by contrast, is placed low in the abdomen and joined to an artery in the pelvis.

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.

An adult human kidney is usually said to be about the size of what?

A fist is the usual comparison: each kidney is about 12 cm long and sits just below the rib cage on either side of the spine, where the lowest ribs give it some protection.

What gland sits on top of each kidney?

Adrenal glands sit like caps on the kidneys but do a different job: the outer cortex makes steroid hormones such as cortisol, and 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 enzyme released by the kidneys starts the cascade that produces angiotensin II and raises blood pressure?

Renin is released when blood pressure in the kidney falls and starts the chain that ends in angiotensin II; the ACE inhibitor family of blood-pressure drugs works by breaking that chain.

Antidiuretic hormone (vasopressin) is released into the blood from which structure at the base of the brain?

Posterior pituitary: vasopressin is made in the hypothalamus but stored and released here; it makes the kidneys conserve water, and alcohol suppresses it, hence the extra bathroom trips.

Which condition, marked by a shortage of or resistance to vasopressin, can push urine output towards 20 litres a day?

Diabetes insipidus has nothing to do with blood sugar: the kidneys simply cannot concentrate urine, so sufferers pass huge volumes and are driven by constant thirst.

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.

The ureters pierce the bladder wall at a slant, an arrangement that works as a natural what?

One-way valve: as the bladder fills it presses the slanted tunnel shut, so urine cannot wash back towards the kidneys; children born without the slant get reflux and repeated infections.

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.

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.

Which type of epithelium lines the bladder and ureters?

Transitional epithelium, also called urothelium, changes shape with the job: its surface cells are plump when the bladder is empty and flatten as it fills, and the lining keeps urine from seeping into the body.

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.

Why do women get urinary tract infections far more often than men?

Their urethra is much shorter, about 4 cm against roughly 20 cm in men, so bacteria from the bowel have a far shorter trip to the bladder.

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 shuts off the bladder during ejaculation, and when it enlarges with age it squeezes the urethra and weakens the stream.

More than nine-tenths of normal human urine is made up of what?

Water makes up well over 90% of urine; the rest is dissolved waste and salts, and the kidneys vary the mix, holding water back when you are dehydrated so the urine turns darker.

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, thought to be what the body breaks into smelly sulphur compounds such as methanethiol; many people never notice, a blind spot linked to variants in their smell-receptor genes.

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 is credited with the line 'money does not stink' after he taxed 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 most kidney stones; small ones often pass on their own while larger ones can lodge in a ureter, and eating normal amounts of calcium helps prevent them rather than cause them.

Which ancient Indian surgeon's Sanskrit treatise gave one of the earliest descriptions of cutting out bladder stones?

Sushruta, author of the Sushruta Samhita, described perineal lithotomy, cutting into the bladder to extract a stone; tradition dates the text to around 600 BC, though scholars now think it took shape over centuries.

Lithotripsy can break up kidney stones without an incision by aiming what at them from outside the body?

Shock waves from a machine outside the body blast the stone into tiny pieces, which then pass out in the urine; the treatment's full name begins 'extracorporeal', meaning outside the body.

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?

Hematuria you can see is called 'gross' by doctors, but more often the blood shows only under a microscope; and red urine is not always blood, since beetroot can tint it too.

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

Nephroblastoma usually shows up as a painless lump in a young child's abdomen, often first noticed by a parent, and about 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.

A study at Zoo Atlanta found that all but the smallest mammals empty their bladders in about how long?

21 seconds, give or take 13, was the near-constant time the researchers measured: larger animals have longer urethras, so gravity drives a faster flow from a bigger bladder.

What is the medical term for producing abnormally large volumes of urine?

Polyuria usually means passing more than about 2.5 to 3 litres a day, against a typical 1 to 2; its opposite, oliguria, is a sharply reduced output, a warning sign of dehydration or failing kidneys.

Which fruit juice has a long-standing reputation as a home remedy for urinary tract infections?

Cranberry may modestly cut the risk of repeat infections in some women, though the findings are inconsistent, and it does not treat an infection once one has started.

Each lobe of the human kidney is built around a striped block of medulla known as what?

A renal pyramid is a cone of medulla whose tip drains urine towards the centre of the kidney; it looks striped because it is packed with straight, parallel tubules and ducts.

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 the term once a child is about five and still wetting the bed; it affects roughly one in six five-year-olds and is usually a developmental delay, not an illness.

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.