50 Fun Facts About Urinary System

Which four organs make up the human urinary system?

The male and female systems are nearly identical; the main difference is the length of the urethra.

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

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

Roughly how many nephrons does each adult human kidney contain?

They do not regenerate, so the number you are born with is the number you have; it declines slowly with age.

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

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.

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

Its inner layer is made of specialised cells called podocytes whose interlocking 'feet' form part of the filtration barrier.

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

Long loops are what let mammals produce concentrated urine; birds have much shorter ones and other vertebrates have none.

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

About 99 percent of it is reabsorbed as it moves along the tubule; the remaining one percent becomes urine.

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

That is roughly 1.25 litres of blood a minute through two organs that together weigh less than a can of soup.

The renal arteries branch directly from which major vessel?

Blood leaves through the renal veins into the inferior vena cava; each artery meets its kidney at the notch called the hilum.

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

Both kidneys move downward when you breathe in, since they sit just below the diaphragm.

About how long is an adult human kidney?

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.

What gland sits on top of each kidney?

It is wrapped in the same two layers of fat as the kidney and shares its protection from the 11th and 12th ribs.

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

Its synthetic version became notorious in endurance sport, but its legitimate use is treating the anaemia of chronic kidney disease.

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

The active form is called calcitriol, which is why advanced kidney disease is often accompanied by bone problems.

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

That is why many blood-pressure drugs (ACE inhibitors, ARBs) target this cascade rather than the heart itself.

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

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.

Diabetes insipidus, in which the body cannot concentrate urine, can produce roughly how much urine a day?

It has nothing to do with blood sugar; the 'central' form is a shortage of vasopressin, the 'nephrogenic' form is kidneys that ignore it.

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

It is made in the outer layer of the gland sitting right on top of the kidney it instructs.

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

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.

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

Flaps of mucosa where the ureters enter the bladder act as valves so urine cannot flow back up when the bladder squeezes.

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

Stretch receptors start signalling the urge at around 300-400 ml, though the bladder can hold considerably more when it must.

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

It can stay relaxed for hours while the bladder fills, then contract for the whole duration of voiding, which most muscles cannot manage.

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

It is three to six cells thick and topped with a mucous glycocalyx that shields the cells beneath from urine.

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

Babies urinate by spinal reflex alone; the higher control that lets you wait develops with toilet training.

Approximately how long is the female urethra?

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.

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

When it enlarges with age it squeezes the urethra, causing the frequency, urgency and dribbling of benign prostatic hyperplasia.

What percentage of urine is water?

The rest is mostly urea, salts and other organic compounds; a healthy person passes about 59 grams of dissolved solids a day.

Which nitrogen waste makes up more than half of the dissolved solids in urine?

It is made in the liver from the ammonia produced when proteins are broken down, then shipped to the kidneys for disposal.

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

The darker the yellow, the more concentrated the urine, which is why colour is a rough hydration gauge.

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

The smell appears within 15 to 30 minutes and fades with a half-life of about four hours; beetroot, by contrast, turns urine pink.

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

'Mellitus' is Latin for honeyed; in 1674 Thomas Willis put the sweet-tasting urine of diabetics into the medical literature.

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

The alchemists never found gold, but the glowing white residue Brand isolated was the first element discovered since antiquity.

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

Nero introduced the tax; fermented urine was valuable to Roman fullers as a cleaning and tanning agent, and was even used to whiten teeth.

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

About 70-80 percent of stones are calcium oxalate; the pain begins when a stone over 5 mm blocks a ureter.

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

Between 1 and 15 percent of people worldwide get a stone in their lifetime, and half of them get another within ten years.

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

It was introduced in the United States in February 1984 and now handles 80-85 percent of simple stones, usually in a 30-60 minute session.

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

His first fifteen patients all died; in 1945 a 67-year-old woman in a uraemic coma woke after 11 hours on the machine, and dialysis was born.

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

Because the Herrick twins were genetically identical there was no rejection; Murray shared the 1990 Nobel Prize for the work.

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

Around 400 million UTIs happen each year; half of all women have at least one in their lifetime.

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

It usually starts as a bladder infection that climbs the ureters, and it brings fever and flank pain on top of the burning.

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?

About 650 cases a year are diagnosed in the United States and roughly 90 percent of children are cured.

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

'Nephro' is Greek and 'renal' is Latin for the same organ, which is why kidney vocabulary is such a mix.

Land mammals over one kilogram all take roughly how long to empty their bladders?

An elephant's bladder holds a thousand times more than a cat's, but its longer urethra lets gravity do the extra work.

Healthy adults normally produce how much urine per day?

Output above 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?

Of about 180 litres of filtrate a day, only around 1% leaves the body as urine.

Who first examined the ureter from the inside, a technique called ureteroscopy, in 1929?

Marshall improved on it with the first published use of a fibre-optic flexible endoscope in 1964.

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

There are eight to 18 such lobes per kidney, and the papilla at each tip drains urine into a minor calyx.

The triangular area of smooth muscle in the bladder floor where the ureters and urethra open is called what?

Mucosal flaps at the ureter openings act as valves against backflow, a failure of which is called vesicoureteral reflux.

At what volume of stored urine do the bladder's stretch receptors typically trigger the urge to urinate?

As the bladder fills, folds called rugae flatten so pressure inside barely rises.