The Organs
The working parts packed inside you — what each one does, and how they team up.
Hover or tap a numbered part to light it up. Tap again to unpin it. You can also move through the parts with the Tab key.
- Control centre
- Breathing
- Blood
- Food
- Cleaning & defence
This drawing is a simplified front view, not an exact anatomical illustration. Organs are drawn slightly separated and shrunk so you can see each one — in a real body they are packed tightly together and overlap. Remember the drawing faces you, so the person’s right is on your left.
An organ is a part of your body built from several kinds of tissue, doing one big job. Your heart is a pump. Your lungs are a gas exchanger. Your liver is a chemical works with hundreds of jobs at once. None of them takes a break, and you never have to think about a single one.
The clever part is the teamwork. Your lungs load oxygen into blood, your heart pushes that blood everywhere, your gut turns lunch into fuel to travel in it, your liver checks and cleans what arrives, and your kidneys throw out what is left over. Take any one away and the others cannot finish their job.
One thing to know before you look at the drawing: this is a body facing you. That means the person's right side is on your left, so the liver looks like it is on the left of the picture even though it sits on the person's right. Doctors always describe organs from the patient's point of view, and so does this page.
All 15 parts, one by one
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What it does
Runs everything. It reads your senses, decides what to do, stores what you learn, and holds your feelings and ideas. Underneath all of that, the stalk at its base quietly keeps your heart beating and your lungs breathing whether you are awake, asleep or thinking about something else entirely.
Find it on you
You cannot touch it, but you can notice it working. Close your eyes and picture your front door. Something in your head just built a picture out of nothing.
Looking after it
Sleep is when your brain sorts and files the day, so it matters more than almost anything. Water, food, movement and quiet time all change how well it works — and a tired brain finds everything harder.
Amazing facts
- It holds around 86 billion nerve cells, each one connected to thousands of others.
- It is only about 2% of your weight but uses about 20% of the energy and oxygen you take in.
- The brain itself has no pain sensors. Brain surgery can be done while the patient is awake and chatting.
- The wrinkles are there to fit more surface into your skull — a bit like scrunching a large sheet of paper into a small box.
86 billion nerve cells- Cerebrum
- The big wrinkled top part, where thinking and memory happen.
- Cerebellum
- The smaller part underneath at the back, in charge of balance and smooth movement.
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What it does
Is the motorway between your brain and your body. Messages about touch, heat and pain travel up it; instructions to your muscles travel down it. For emergencies it does not even bother asking the brain — pull your hand off something hot and the cord has already ordered the movement before your brain knows.
Find it on you
Tap just below your kneecap with the edge of your hand while your leg dangles loose. If your leg kicks, that is a reflex your spinal cord ran without asking permission.
Looking after it
It is precious and does not repair well, so it is worth protecting: seatbelts, helmets, and never diving into water when you do not know how deep it is.
Amazing facts
- It is around 45 cm long and stops about two thirds of the way down your back, near the bottom of your ribs. Below that it becomes a spray of loose nerves.
- Nerve messages can travel at over 100 metres per second — faster than a racing car.
- It is only about as thick as your little finger.
- Nerve
- A bundle of fibres carrying electrical messages around the body.
- Reflex
- An automatic movement decided by the spinal cord, not the brain.
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What it does
Swaps gases. Air travels down your windpipe, splits into smaller and smaller tubes, and ends in millions of tiny bubbles wrapped in blood vessels. Oxygen crosses out of the bubbles into your blood and waste carbon dioxide crosses back in, ready to be breathed out.
Find it on you
Put a hand on your chest and breathe in slowly through your nose until you cannot fit any more air, then let it out. That slow rise and fall is your lungs filling and emptying.
Looking after it
Fresh air and exercise stretch your lungs and keep them working well. Smoke and vape fumes damage the tiny bubbles permanently — they never grow back.
Amazing facts
- There are around 300 to 500 million tiny air sacs inside your lungs. Unfolded flat they would cover roughly half a tennis court.
- Your lungs are not the same size. The left one is smaller and has a dent in it to make room for your heart.
- They are the only organs in your body that can float in water.
- You breathe about 20,000 times a day without deciding to once.
~20,000 breaths a day- Alveoli
- The millions of tiny air sacs where oxygen crosses into the blood.
- Trachea
- The windpipe, the tube carrying air from your throat to your lungs.
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What it does
Does the actual work of breathing. Your lungs have no muscles of their own. When the diaphragm tightens it flattens downwards, making the space above it bigger, and air rushes in to fill it. Let it relax and it domes back up, pushing air out.
Find it on you
Lie down and rest a hand on your belly, just below your ribs. Breathe in and your hand should rise. That is your diaphragm pushing down — it is what people mean by belly breathing.
Looking after it
Slow belly breathing, longer out than in, is one of the fastest ways to settle a panicky or overwhelmed body. It is a real physical switch, not just a distraction.
Amazing facts
- A hiccup is your diaphragm twitching suddenly, and the "hic" is your voice box snapping shut on the rush of air.
- It is the hardest working muscle you own — it never gets a day off, not even while you sleep.
- Diaphragm
- The dome of muscle under the lungs that drives breathing.
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What it does
Runs two pumps side by side. The right half sends tired blood a short way to your lungs to pick up oxygen. The left half takes it back and pushes it, much harder, all the way round your body and back again. Valves between the chambers slam shut to stop blood sliding backwards — that slamming is the "lub-dub" you hear.
Find it on you
Press two fingers gently on the thumb side of your wrist, or on your neck beside your windpipe. That tapping is a wave of pressure from your heart squeezing, arriving a fraction of a second later.
Looking after it
Your heart is a muscle, so it gets stronger when you make it work. Anything that leaves you a bit out of breath — running, dancing, cycling, swimming — trains it.
Amazing facts
- It beats around 100,000 times a day, and roughly 2.5 billion times in an average lifetime.
- It pumps about 5 litres of blood every minute, which is your entire blood supply, every minute.
- It makes its own electricity. A patch of cells in the top right chamber fires the beat, which is why a heart can keep beating outside the body.
- A child’s heart beats faster than an adult’s because it is smaller and has to work more often to move the same blood.
~100,000 beats a day- Atrium
- One of the two upper chambers, which receive blood coming in.
- Ventricle
- One of the two lower chambers, which pump blood out.
- Valve
- A one-way flap stopping blood from flowing backwards.
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What it does
Is a mixing tank, not a rubbish bin. Muscular walls churn your food while strong acid and enzymes attack it, until a solid meal becomes a thick soup. The acid also kills most germs that arrive with your dinner. A few hours later it squeezes the soup on into your small intestine.
Find it on you
Put a hand on the left side of your body, just below your ribs. That is roughly where it sits — higher and further left than most people expect.
Looking after it
Eating slowly and chewing properly gives it much less work to do. Rushing a meal is a common cause of tummy ache.
Amazing facts
- Stomach acid is strong enough to damage metal. Your stomach survives because it makes a fresh coat of slippery mucus every few days.
- It stretches. Empty it is about the size of a fist; after a big meal it can hold well over a litre.
- A rumbling tummy is not hunger itself — it is the muscles squeezing air and juices along an empty tube.
- Enzyme
- A chemical tool that chops food into smaller pieces.
- Mucus
- Slippery slime that coats and protects the lining.
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What it does
Is your chemical works. Every drop of blood leaving your gut goes through the liver first, where it is checked over: useful things are stored, poisons are broken down, and spare sugar is packed away for later. It also makes bile, the green-yellow liquid that breaks fat into droplets small enough to digest.
Find it on you
Feel the bottom edge of your ribs on your right side. Your liver sits just behind and above there, which is why doctors press under the right ribs when your tummy hurts.
Looking after it
It handles everything you swallow, which is why alcohol and some medicines damage it over time. It is also happiest when you are a healthy weight and eat plenty of plants.
Amazing facts
- It does more than 500 different jobs. No machine has ever been built that can replace it.
- It is the only organ that can regrow. Remove a large part of a healthy liver and it can rebuild itself back to full size.
- It weighs around 1.5 kg — heavier than your brain.
Over 500 jobs- Bile
- A liquid made by the liver that breaks fat into tiny droplets.
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What it does
Is the bile store. The liver makes bile all day long, but you only need it when fatty food arrives. So the gallbladder collects it, squeezes the water out to make it stronger, and then contracts to squirt it into your small intestine exactly when a fatty meal shows up.
Find it on you
It is too small and too well hidden to feel from outside — it sits behind the lower edge of your ribs on the right, under the liver.
Looking after it
Bile can sometimes harden into stones, which hurt when they block the exit. A diet with plenty of fibre and not too much fried food makes that less likely.
Amazing facts
- You can live perfectly well without it. If it is removed, bile simply drips straight from the liver into the intestine all the time.
- It only holds about 50 ml — a couple of tablespoons — but that bile is many times more concentrated than when it left the liver.
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What it does
Holds down two completely different jobs. Most of it makes powerful digestive juice that pours into the small intestine to break down fat, protein and starch. Scattered through it are small islands of cells doing something else entirely: making insulin, the hormone that tells your body to take sugar out of the blood and use or store it.
Find it on you
You cannot feel it. It hides behind your stomach, right up against your spine, which is why problems there are often felt as pain going through to the back.
Looking after it
The insulin cells work steadily best when meals are balanced rather than a constant stream of sugary drinks and snacks.
Amazing facts
- In type 1 diabetes the insulin-making cells stop working, so insulin has to be given as medicine instead. It is nobody’s fault and nothing to do with eating sweets.
- Its digestive juice is so powerful that it is made and stored in a switched-off form, and only activated once it is safely inside the intestine.
- Hormone
- A chemical message sent through the blood to tell organs what to do.
- Insulin
- The hormone that lets your body take sugar out of the blood.
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What it does
Is where you actually get fed. Everything before this was preparation. Here, juices from the pancreas and bile from the liver finish breaking food down, and the goodness passes through the wall into your blood. The lining is covered in millions of tiny finger-like bumps that make the surface enormously bigger, so almost nothing useful is missed.
Find it on you
Press gently around your belly button. The coils sitting behind there are your small intestine, with the large intestine framing them.
Looking after it
Fibre from fruit, vegetables, beans and wholegrains keeps everything moving at a comfortable speed. Drinking enough water matters just as much.
Amazing facts
- It is around four times longer than you are tall, packed into your middle by folding.
- The tiny finger-like bumps, called villi, make the inside surface about the size of a small room’s floor.
- Food spends roughly 3 to 5 hours travelling through it.
About 6 metres long- Villi
- Tiny finger-shaped bumps lining the intestine that soak up food.
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What it does
Recovers what is left. By now the useful food is gone, so this stretch reclaims water and salts, turning a sloppy liquid into something solid enough to store and pass. It is also home to trillions of helpful bacteria that feed on fibre you cannot digest and make vitamins for you in return.
Find it on you
Trace a square with your hand around your belly button: up the right side, across under your ribs, and down the left. That is the route it takes.
Looking after it
Your gut bacteria live on plant fibre, so the more different plants you eat, the more varied and healthy that community becomes.
Amazing facts
- You carry trillions of bacteria in here — roughly as many cells as your whole body is made of.
- They make vitamin K and several B vitamins that you cannot make for yourself.
- Leftovers spend between 12 and 48 hours in here, far longer than anywhere else in the journey.
- Microbiome
- The huge community of helpful bacteria living in your gut.
- Fibre
- The part of plants you cannot digest, which feeds your gut bacteria.
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What it does
Cleans your blood, all day, every day. Blood is pushed through about a million tiny filters in each kidney. Almost everything is squeezed out, then the useful parts — water, sugar, salts — are carefully taken back, and what is genuinely waste heads off to the bladder as urine. They also help control your blood pressure and tell your marrow when to make more red blood cells.
Find it on you
Put your hands on your lower back either side of your spine, just under the bottom ribs. They sit deep behind there, further up than most people guess.
Looking after it
Drinking water through the day makes their job easier. Pale straw-coloured wee usually means you have had enough.
Amazing facts
- Together they filter around 180 litres of fluid a day, then take back almost all of it. You only pass 1 to 2 litres.
- Each kidney holds about a million tiny filters called nephrons.
- Your right kidney sits slightly lower than the left, because the liver takes up the room above it.
180 litres filtered a day- Nephron
- One of the million tiny filter units inside each kidney.
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What it does
Is the storage tank, so you do not have to wee constantly. Urine trickles down from both kidneys and collects here, and the walls stretch thinner as it fills. Stretch sensors tell your brain when it is getting full, and a ring of muscle at the exit stays clamped shut until you decide otherwise.
Find it on you
Low down in the middle, behind your pubic bone. You know exactly where it is when it is full.
Looking after it
Going when you need to go is kinder to it than holding on for hours, which stretches it and can bring on infections.
Amazing facts
- It usually starts nudging you at around 200 ml but can hold more than double that.
- Learning to control the exit muscle is one of the first big jobs a toddler brain learns, and it takes longer for some children than others. That is normal.
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What it does
Is a filter and a guard post. It pulls worn-out red blood cells out of circulation and recycles the iron from them, and it keeps a large stock of white blood cells ready to attack germs that turn up in the blood. It also holds a reserve of blood it can squeeze out in an emergency.
Find it on you
It hides completely behind the lower left ribs. A healthy one cannot be felt from outside at all.
Looking after it
Because it sits right under the ribs, a hard blow to the left side can damage it. That is one reason for pads and proper technique in contact sports.
Amazing facts
- Red blood cells live for about 120 days. The spleen is where the old ones are taken apart.
- You can live without a spleen, but you catch certain infections more easily afterwards, so people who lose theirs need extra vaccinations.
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What it does
Is a barrier, a thermostat and a sense organ at once. It keeps water and germs out, keeps your insides in, and holds a huge number of tiny sensors for touch, pressure, heat and pain. When you overheat it sweats to cool you and opens its blood vessels to dump heat, which is why you go red.
Find it on you
Look at the back of your hand under a light. Those fine criss-cross lines are the flexible folds that stop your skin tearing when you make a fist.
Looking after it
Sun cream and shade protect it from burning, which damages it permanently. Washing hands well is the single most effective way to stop germs spreading.
Amazing facts
- Spread flat, an adult’s skin would cover about 2 square metres.
- You shed tens of thousands of dead skin cells every minute, and grow a whole new outer layer roughly every month.
- Your skin makes vitamin D when sunlight hits it — one of the very few things your body cannot get enough of from food alone.
About 2 square metres- Epidermis
- The thin tough outer layer you can see and touch.
- Dermis
- The thicker layer underneath, holding nerves, sweat glands and blood vessels.