50 free Urinary System trivia questions with answers — science & nature quiz, new questions added Aug 2026.
Your kidneys filter about 180 litres of fluid a day and hand back 99 percent of it, which is why you produce a litre or two of urine rather than a bathtub. This urinary system trivia quiz covers the anatomy and physiology students actually need to know: the four organs of the system, the nephron and its parts (glomerulus, Bowman's capsule, loop of Henle), how much blood the kidneys receive, the hormones that decide how much water you keep, what urine is made of and why it is yellow. It also digs into the clinical and historical side: the most common kind of kidney stone, the Dutch doctor who built the first dialysis machine from sausage casings, the first successful kidney transplant, why urinary infections are more common in women, the Roman emperor who taxed urine, and the alchemist who discovered phosphorus by boiling it. Easy questions for a biology class or a health-science revision session, harder ones for nursing and pre-med students. Every answer was checked against Wikipedia's articles on the urinary system, kidney, nephron, bladder, urine and the people involved, and each question quotes its source.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Which four organs make up the human urinary system?
Kidneys, ureters, bladder, urethra
The male and female systems are nearly identical; the main difference is the length of the urethra.
Q 02What is the basic structural and functional unit of the kidney?
Nephron
Each adult kidney contains around a million of them; a mouse kidney gets by with about 12,500.
Q 03Roughly how many nephrons does each adult human kidney contain?
About 1 million
They do not regenerate, so the number you are born with is the number you have; it declines slowly with age.
Q 04The tuft of filtering capillaries at the start of each kidney filtration unit is called what?
Glomerulus
Only about a fifth of the plasma passing through it is filtered; the rest carries on into a narrower efferent arteriole, which is what keeps the pressure up.
Q 05The cup-shaped structure that surrounds the kidney's filtering capillary tuft is named after which anatomist?
Bowman
Its inner layer is made of specialised cells called podocytes whose interlocking 'feet' form part of the filtration barrier.
Q 06Which U-shaped section of the kidney tubule dips down into the renal medulla?
Loop of Henle
Long loops are what let mammals produce concentrated urine; birds have much shorter ones and other vertebrates have none.
Q 07The glomerular filtration rate of a healthy adult amounts to roughly how much filtrate per day?
180 litres
About 99 percent of it is reabsorbed as it moves along the tubule; the remaining one percent becomes urine.
Q 08What share of the heart's output goes to the kidneys in a healthy adult?
About 20-25%
That is roughly 1.25 litres of blood a minute through two organs that together weigh less than a can of soup.
Q 09The renal arteries branch directly from which major vessel?
Abdominal aorta
Blood leaves through the renal veins into the inferior vena cava; each artery meets its kidney at the notch called the hilum.
Q 10Which kidney usually sits slightly lower in the body, and why?
The right, because of the liver
Both kidneys move downward when you breathe in, since they sit just below the diaphragm.
Q 11About how long is an adult human kidney?
12 cm
A Danish study measured medians of 11.2 cm on the left and 10.9 cm on the right, with the left kidney also slightly larger by volume.
Q 12What gland sits on top of each kidney?
Adrenal
It is wrapped in the same two layers of fat as the kidney and shares its protection from the 11th and 12th ribs.
Q 13Which kidney hormone, released in response to low oxygen, stimulates red blood cell production?
Erythropoietin
Its synthetic version became notorious in endurance sport, but its legitimate use is treating the anaemia of chronic kidney disease.
Q 21The typical adult bladder comfortably holds how much urine before urination?
300-500 ml
Stretch receptors start signalling the urge at around 300-400 ml, though the bladder can hold considerably more when it must.
Q 22What is the name of the smooth muscle in the bladder wall that contracts to expel urine?
Detrusor
It can stay relaxed for hours while the bladder fills, then contract for the whole duration of voiding, which most muscles cannot manage.
Q 23What is the stretchy urinary-tract lining that flattens as the bladder fills?
Urothelium
It is three to six cells thick and topped with a mucous glycocalyx that shields the cells beneath from urine.
Q 14The kidneys convert a precursor into the active form of which vitamin?
D
The active form is called calcitriol, which is why advanced kidney disease is often accompanied by bone problems.
Q 15Which kidney enzyme is the first messenger in the cascade ending with angiotensin II raising blood pressure?
Renin
That is why many blood-pressure drugs (ACE inhibitors, ARBs) target this cascade rather than the heart itself.
Q 16Antidiuretic hormone (vasopressin) is released from which part of the brain?
Posterior pituitary
It tells the kidney's collecting ducts to insert aquaporin water channels and hang on to water; alcohol suppresses it, which is why beer sends you to the bathroom.
Q 17Diabetes insipidus, in which the body cannot concentrate urine, can produce roughly how much urine a day?
Nearly 20 litres
It has nothing to do with blood sugar; the 'central' form is a shortage of vasopressin, the 'nephrogenic' form is kidneys that ignore it.
Q 18Which hormone acts on the distal tubules to increase sodium reabsorption, raising blood pressure?
Aldosterone
It is made in the outer layer of the gland sitting right on top of the kidney it instructs.
Q 19How long are the adult human ureters, the tubes carrying urine from kidney to bladder?
20-30 cm
They are only 3-4 mm wide and push urine along by peristalsis, muscular waves like those of the gut, so urine flows even when you are lying down.
Q 20What is the name of the wave-like muscular contraction that moves urine down the ureters?
Peristalsis
Flaps of mucosa where the ureters enter the bladder act as valves so urine cannot flow back up when the bladder squeezes.
Q 24The micturition centre that controls urination sits in which part of the brain?
The brainstem
Babies urinate by spinal reflex alone; the higher control that lets you wait develops with toilet training.
Q 25Approximately how long is the female urethra?
About 4 cm
The male urethra averages 18-20 cm because it runs through the penis; the short female one is a major reason urinary infections are more common in women.
Q 26Which gland below the male bladder acts as a switch between urination and ejaculation?
Prostate
When it enlarges with age it squeezes the urethra, causing the frequency, urgency and dribbling of benign prostatic hyperplasia.
Q 27What percentage of urine is water?
91-96%
The rest is mostly urea, salts and other organic compounds; a healthy person passes about 59 grams of dissolved solids a day.
Q 28Which nitrogen waste makes up more than half of the dissolved solids in urine?
Urea
It is made in the liver from the ammonia produced when proteins are broken down, then shipped to the kidneys for disposal.
Q 29Which pigment, a breakdown product of haemoglobin, gives urine its yellow colour?
Urobilin
The darker the yellow, the more concentrated the urine, which is why colour is a rough hydration gauge.
Q 30Eating which vegetable gives some people's urine a distinctive smell from a sulphur compound named after it?
Asparagus
The smell appears within 15 to 30 minutes and fades with a half-life of about four hours; beetroot, by contrast, turns urine pink.