50 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.