The Drip-Drop Club

A 3D tour of the kidneys that follows a tiny bit of urea from the liver, through one of the kidneys' tiny filters, down to the bladder and out, for children about five to eight. Free, with no ads and no sign-ups.

What your child will learn

• You have two kidneys, shaped like beans and about the size of your fist. They sit at your back, just under your ribs: put your hands on your hips, slide them up to your ribs, and your thumbs are close.
• Your kidneys clean your blood. They filter all of it about 40 times a day.
• Inside each kidney are about a million tiny filters called nephrons. The blood goes through a sieve, the glomerulus: blood cells stay in the blood, and water and waste go through.
• Then a long tube, the tubule, takes back what your body still needs (sugar, salt and most of the water). Part of it dips deep in a U-bend, the loop of Henle, which helps your kidneys save water. What's left, the waste and a little water, makes wee.
• Urea is one of those wastes. Your liver makes it from used-up protein, and your kidneys send it out in your wee.
• Wee goes down two tubes called ureters to your bladder, which stretches like a balloon. When it's about half full, it tells your brain it's time to go. Wee leaves through the urethra.
• Wee is mostly water. It's pale when you've had plenty to drink. When you need a drink, your brain tells your kidneys to save water, so there's less wee, and it's darker.

How it works

Story. A platypus tells it in eight short chapters. The camera follows a tiny bit of urea (a two-lobed bead wearing an orange ring) from the liver, where the Mix-Fix Club left it, round through the heart and into a kidney. A close-up follows it through one nephron: the sieve, the tubule, the loop of Henle and the collecting duct. Then it goes down a ureter into the bladder, which fills and stretches until a message zips up to the brain and a "Time to go!" door appears. The Tasmanian devil and the echidna drop in from their own tours. Every word is spoken and shown.

Explore. Turn the body round, peek inside a kidney (it opens like a bean cut in half), or tap any part to hear what it does. Two buttons change what the body is doing: Drink (more wee, and pale) and Play (a hot run: less wee, and darker, and in the close-up the brain's save-water message opens the water doors). Follow the urea goes the whole way, again and again, and What's this? shows the parts one at a time, including the close-up.

Quiz. Six picture questions, read aloud, so it works before your child can read. A wrong answer greys out and they have another go; nothing is ever lost. Finishing brings a new animal for their My mob book, and a card of the words they now know.

The real words it teaches

The tour uses the real names for the parts, and says what each one means the first time. These are on the card at the end, and a tap on each says what it means. The loop of Henle and the collecting duct are named in the story, and the renal artery, vein and pelvis in Explore, but they're kept off the card.

• Kidneys: two bean-shaped parts at your back that clean your blood and make wee.
• Nephrons: the million tiny filters inside each kidney.
• Glomerulus: the nephron's sieve. Water and waste go through, and blood cells stay.
• Tubule: the long tube that takes back what your body still needs.
• Urea: a waste your liver makes, which leaves in your wee.
• Ureters: the two tubes that carry wee down to your bladder.
• Bladder: the stretchy bag that holds your wee until you go.
• Urethra: the tube wee leaves through.

For grown-ups: inside a nephron, in detail

The close-up in chapters 3, 4 and 7 is one nephron, drawn big and simple. What it shows, cartoon but true:

1. Filtration. Blood arrives in a tiny artery (the afferent arteriole) and runs through the glomerulus, a knot of capillaries inside a cup, Bowman's capsule. Water and small molecules, such as glucose, salts and urea, are pushed through into the capsule; blood cells and most proteins are too big, and stay in the blood.
2. The proximal tubule takes back all the glucose and most of the sodium and water, into the capillaries running alongside.
3. The loop of Henle dips into the medulla. Its descending limb lets water out; its ascending limb pumps salt out but lets no water through. That keeps the deep part of the kidney salty, which is what draws water out of the descending limb and, later, the collecting duct.
4. The distal tubule and collecting duct. When the body needs to save water, the pituitary releases ADH (antidiuretic hormone, or vasopressin), the tour's "save-water message", drawn as a purple key. It puts water channels (aquaporins, the "water doors") into the collecting duct, so more water goes back to the blood and the urine is more concentrated: less wee, and darker.
5. Out. What's left (urea and other wastes, and the leftover water) drains into the renal pelvis, down a ureter to the bladder, and out through the urethra.

An adult's kidneys filter about 150 quarts (about 140 litres) of blood a day and make only 1 to 2 quarts of urine. The kidneys have other jobs the tour leaves for later: they make hormones that help control blood pressure, make red blood cells and keep bones strong.

What it practises

• My body. How the body works, and the real names of its parts: the heart's atria and ventricles, arteries and veins (the Lub-Dub Club).
  AC9S1U01 (Science, Year 1); AC9HPFM03 (Health and Physical Education, Foundation)

The codes are from the Australian Curriculum v9 (Foundation to Year 1). Each links to the official wording.

Things to try together

• Find your kidneys: hands on hips, slide them up to your ribs, and your thumbs are close.
• Make a fist: each kidney is about that big.
• After a big drink, and after running about on a hot day, notice the colour of wee together: pale, or a bit darker? Both are fine. Darker just means it's time for a drink.
• The sheet to print has the kidneys, bladder and tubes to label, "Back or out?" (what the tubule takes back into the blood, and what goes out in the wee), and a drip-drop day: a drop to colour for every drink.

The tour says nothing about illness: no kidney disease, stones, infections, dialysis or transplants, and nothing about wee as a warning sign. Wee is shown plainly and kindly, as a drip at the end of a tube and a cartoon toilet door, and "everybody does it". Water is never a rule: "drink water when you're thirsty, and go when you need to", with no amounts and no good or bad drinks.

What's simplified, and why

• The kidneys are drawn a little big for the body, like the other tours' organs, so they're easy to find. Their shape and place are true: at the back, under the lower ribs, either side of the backbone, the right one a little lower because the liver sits above it.
• 'About 40 times a day' is the kids' figure from KidsHealth. The adult figures (about 150 quarts filtered, 1 to 2 quarts of urine a day) stay in the guide.
• 'About a million filters' is per kidney. Some pages say 'more than a million' across both, so the tour says 'about a million in each kidney'.
• The way from the liver to the kidneys really goes through the heart and the lungs and back to the heart. The tour says 'round, through your heart' and leaves the lungs out.
• The close-up draws one nephron big and simple. The short twist after the loop of Henle (the distal tubule) is drawn as part of the way to the collecting duct, and proteins aren't shown: the guide says they're too big to go through, like the blood cells.
• 'About half full' is when a child first feels the need to go, not the most the bladder holds.
• The brain's save-water message is ADH (vasopressin). The tour calls it the brain's save-water message and draws it as a little purple key.
• In the close-up, the tiny blood vessels round the tubule (really a mesh of capillaries, with long hairpin ones beside the loop) are drawn as one vessel running alongside, so what's taken back has a short hop into the blood. The water doors in the collecting duct stand for the water channels the save-water message puts in its wall.

Where the facts come from

Every fact the tour states was checked against the page linked beside it.

• Two bean-shaped organs, each about the size of a fist, just below the rib cage, one on each side of the spine.
  In the tour: These are your kidneys. You have two, each about the size of your fist. They sit at your back, just under your ribs, one on each side of your backbone.
  NIDDK — Your Kidneys & How They Work
• "Put your hands on your hips, then slide your hands up until you can feel your ribs. Now if you put your thumbs on your back, you will know where your kidneys are."
  In the tour: Put your hands on your hips and slide them up to your ribs. Your kidneys are near your thumbs!
  KidsHealth (kids) — Your Kidneys
• The kidneys filter the blood about 40 times a day.
  In the tour: Your kidneys clean all your blood about forty times a day!
  KidsHealth (kids) — Your Kidneys
• Each kidney contains about one million tiny units called nephrons.
  In the tour: Each kidney has about a million tiny filters called nephrons.
  Better Health Channel — Kidneys
• The glomerulus lets smaller molecules, wastes and fluid (mostly water) pass into the tubule; larger molecules, such as proteins and blood cells, stay in the blood.
  In the tour: Here's the glomerulus: the nephron's sieve. Blood cells are too big to get through, so they stay in your blood. But water, sugar, salt and our urea squeeze through!
  NIDDK — Your Kidneys & How They Work
• The tubule returns needed substances to the blood and removes wastes.
  In the tour: It passes everything your body still needs back into your blood: all the sugar, and most of the salt and water.
  NIDDK — Your Kidneys & How They Work
• The loop of Henle's descending limb is permeable to water; its ascending limb is impervious to water but permeable to solutes, and the salt pumped out helps water flow out of the descending limb.
  In the tour: Then the loop of Henle: a U-bend that dips deep. It helps your kidneys save water.
  StatPearls — Histology, Nephron (NCBI)
• ADH (vasopressin) increases water reabsorption in the late distal tubule and collecting duct, and lets the body conserve water in times of dehydration.
  In the tour: Your brain tells your kidneys to save water. See the purple key? It opens little water doors, so more water goes back into your blood. So there's less wee, and it's darker.
  StatPearls — Physiology, Vasopressin (NCBI)
• The kidneys filter about 150 quarts of blood a day but make only 1 to 2 quarts of urine (adult figures).
  In the tour: (the guide) Only a little of all that becomes wee.
  NIDDK — Your Kidneys & How They Work
• The liver turns toxic ammonia into urea, which is excreted in the urine.
  In the tour: Your liver makes a waste called urea.
  StatPearls — Physiology, Urea Cycle (NCBI)
• Urea nitrogen is a waste product that forms as the body breaks down proteins, and the kidneys remove it in urine.
  In the tour: It's left over from your body using protein.
  MedlinePlus — BUN (Blood Urea Nitrogen) test
• Urine slides down a long tube called the ureter and collects in the bladder, a storage sac; there are two ureters, thin tubes of muscle.
  In the tour: Down a tube called a ureter it goes, drip, drop. Into your bladder, a stretchy bag, like a balloon.
  KidsHealth (kids) — Your Kidneys
• When the bladder is about halfway full, the body signals that it's time to go to the bathroom.
  In the tour: When it's about half full, it sends a message to your brain: time to go!
  KidsHealth (kids) — Your Kidneys
• Urine goes from the bladder down another tube called the urethra and out of the body.
  In the tour: Out it goes, through a tube called the urethra.
  KidsHealth (kids) — Your Kidneys
• Between 91% and 96% of healthy urine is excess water; the rest includes salt and urea.
  In the tour: Wee is mostly water, with a little waste.
  Cleveland Clinic — Urine
• Light yellow urine means you're drinking enough; with less fluid, urine has less water in it and looks darker.
  In the tour: Had lots to drink? You'll make more wee, and it's pale. Less wee, and darker: time for a drink!
  Cleveland Clinic — Urine
• The kidneys maintain body fluid at the correct levels for the body to function.
  In the tour: Your kidneys keep the water in your body just right.
  Better Health Channel — Kidneys
• The kidneys make hormones that help control blood pressure, make red blood cells and keep bones strong.
  In the tour: (the guide) The kidneys' other jobs.
  NIDDK — Your Kidneys & How They Work
• A platypus makes a soft, querulous growl when annoyed.
  In the tour: The platypus's little growl (a sound, not a line).
  Australian Platypus Conservancy — Platypus communication

Every word it says

The whole script, for reading along, or for a child who'd rather read than listen.

1. Drip, drop

• Hello! I'm Platypus. Drip, drop!
• These are your kidneys. You have two, each about the size of your fist.
• They sit at your back, just under your ribs, one on each side of your backbone.
• Put your hands on your hips and slide them up to your ribs. Your kidneys are near your thumbs!

2. Something to clean

• Remember the liver's clean-up? Tasmanian devil does!
• Your liver makes a waste called urea. It's left over from your body using protein.
• Out it goes, into your blood, and round through your heart.
• Then down the aorta, and into the renal artery: the kidney's own artery.

3. A million filters

• Let's look really closely! Each kidney has about a million tiny filters called nephrons.
• Here's the glomerulus: the nephron's sieve. Blood cells are too big to get through, so they stay in your blood.
• But water, sugar, salt and our urea squeeze through!

4. Take it back

• Next, the tubule: a long, twisty tube.
• It passes everything your body still needs back into your blood: all the sugar, and most of the salt and water.
• Then the loop of Henle: a U-bend that dips deep. It helps your kidneys save water.
• But not the urea! On it goes, down the collecting duct.
• Leftover water and waste make wee!

5. Down to the bladder

• Down a tube called a ureter it goes, drip, drop.
• Into your bladder, a stretchy bag, like a balloon.
• When it's about half full, it sends a message to your brain: time to go!
• Zip! Echidna from the Zip-Zap Club heard that one.

6. Time to go!

• Off to the toilet! Out it goes, through a tube called the urethra.
• Wee is mostly water, with a little waste. Everybody does it.
• Flush! And wash your hands.

7. Just right

• Your kidneys keep the water in your body just right.
• Had lots to drink? You'll make more wee, and it's pale.
• Played hard on a hot day? Your brain tells your kidneys to save water.
• See the purple key? It opens little water doors, so more water goes back into your blood.
• So there's less wee, and it's darker: time for a drink!

8. Look after your kidneys

• Your kidneys clean all your blood about forty times a day!
• Drink water when you're thirsty, and go when you need to.
• Thanks for dripping and dropping with me. Welcome to the Drip-Drop Club!

The quiz

Quiz time! Let's see what you remember. The right answers are in bold.

1. Where are your kidneys? (In your head / At your back, under your ribs / In your feet)
2. What do your kidneys make? (Wee / Tears / Hair)
3. What are the kidneys' tiny filters called? (Teeth / Freckles / Nephrons)
4. Where does wee wait until you go? (Your stomach / Your bladder / Your heart)
5. What is wee mostly made of? (Water / Sand / Milk)
6. Your wee is dark yellow after playing on a hot day. What would help? (A nap / A hat / A drink of water)

For every child

• Every word is spoken and written, so it works with the sound on or off.
• It works with a keyboard: the arrow keys turn the body in Explore, and What's this? steps through the parts.
• The water, sugar, salt and urea in the close-up each have their own shape as well as colour.
• If your device asks for less motion, the camera cuts instead of flying, the page turns without the iris, and nothing bobs or wobbles.

What it needs, and what we collect

A recent browser on a phone, tablet or computer. The first visit downloads about 9 MB, and after that it keeps working with no signal. Nothing about your child is collected: the My mob card and the sound setting are kept on your own device. The privacy page has the whole story.

More in the series: What Makes Me, with the Lub-Dub Club, the Huff-Puff Club, the Munch-Crunch Club, the Mix-Fix Club and the Zip-Zap Club.