The human body

Your whole body is built from tiny pieces: cells. Come and see what is inside a cell and how your body uses cells to grow and heal.

You are made of cells · Your body grows and heals

Your skin wraps around you like a coat and does all sorts of things for you all day long. Come and see how your skin protects you, how it keeps you cool and how to look after it in the sun.

Your skin protects you · Sweat, goosebumps and the sun

Inside your body there is a strong frame of bones. Come and see how your bones hold you up and protect you, and how your joints let you bend.

Your bones hold you up · Joints let you bend

Your muscles let you run, jump and wave. Come and see how your muscles pull on your bones, and which muscles work all by themselves without you noticing.

Muscles pull · Muscles you can't feel

You use your brain to think, feel and remember, and it talks to your whole body through your nerves. Come and see how messages travel back and forth, and what your brain does while you sleep.

Messages through your body · Sleeping

With your eyes, ears, nose, tongue and skin you notice what is going on around you. They send messages to your brain, and that is where you see, hear, smell, taste and feel it.

Seeing and hearing · Smelling, tasting and feeling

Your body doesn't only send messages along your nerves, but also with tiny substances in your blood: hormones. Come and see where they come from and what happens when you get a fright.

Messengers in your blood · Getting a fright

Deep inside your chest there is a muscle that never stops: your heart. Come and see what it does all day long.

Your heart is a pump · A trip around your body

Tiny helpers swim around in your blood and look after you all day long. Come and see what they do, even when you fall over.

What is in your blood? · A scab on your knee

You breathe all day and all night, without even thinking about it. Come and see where the air goes, and why you sometimes cough, sneeze or hiccup.

In and out · Coughing, sneezing and hiccups

Every bite you take goes on a long journey through your body. Come and see where your food goes, and what is left at the end.

The journey of a sandwich · Goodness in, poo out

Your kidneys work for you all day long, even while you sleep. Come and see how they clean your blood and how your wee is made.

Your kidneys clean your blood · Water in and water out

Everything in your body is built from cells. In this chapter you will see what is inside a cell, how cells together form tissues and organs, and how your body grows and repairs itself.

You are made of cells · From cell to organ · Your body grows and heals

Your skin is your largest organ and does many things at once: protecting you, feeling and controlling your temperature. In this chapter you will see which layers your skin is made of, how you feel with it, and how it keeps you cool and warm and protects you from the sun.

Your skin protects you · Feeling with your skin · Sweat, goosebumps and the sun

Your skeleton holds you up, protects your organs and, together with your muscles, lets you move. In this chapter you will see which bones you have, how joints work, and how your bones grow and stay strong.

Your skeleton · Joints and ligaments · Strong bones

Your muscles let you move, hold you upright and make heat. In this chapter you will see how muscles contract, which three kinds of muscle you have, and what happens when you get tired or stronger.

Muscles and tendons · Three kinds of muscle · Tired, stronger and sore

Your nervous system passes on messages, from your skin to your brain and from your brain to your muscles. In this chapter you will see how a nerve cell works, how your brain is built, and what reflexes, sleep and practice do to your brain.

Nerve cells · Brain, spinal cord and nerves · Reflexes, sleep and learning

Your senses pick up stimuli such as light, sound and smell molecules, but seeing, hearing and smelling only happen in your brain. In this chapter you will see how your eye, your ear and your balance organ work, and how you smell, taste and feel.

The eye · The ear and your balance · Smell, taste, touch and pain

Hormones are messengers that travel through your whole body in your blood. In this chapter you will see which glands make them, how your body controls your blood sugar, what happens during stress, and how hormones make you grow and grow up.

Glands and hormones · Blood sugar and insulin · Fright and stress · Growing and puberty

Your heart has four chambers and pumps your blood around two circuits: one through your lungs and one through the rest of your body.

Your heart is a pump · A trip around your body · Feel your heartbeat

Your blood carries oxygen, closes up cuts and helps your immune system fight germs. In this chapter you will see how that works.

What is in your blood? · A cut that closes up · Germs and your immune system

Every breath brings oxygen to your blood and carries carbon dioxide back out. In this chapter you will see how your lungs do that, and how they keep themselves clean.

In and out · What your lungs do with air · Coughing, sneezing and hiccups

From your mouth to your rectum, your body breaks food down and takes out what it needs. In this chapter you see how that works, and what part your liver and your gut bacteria play in it.

The journey of a sandwich · What your body gets out of food · Drinking and pooing

Every day your kidneys filter a huge amount of fluid out of your blood and take most of it back again. In this chapter you will see how that works, how your body keeps its water at the right level, and where the colour of your wee comes from.

Your kidneys clean your blood · Water in and water out · Why is wee yellow?

Everything in your body starts with cells. In this chapter you will see what is inside a cell, how substances get in and out, how a cell divides, which four kinds of tissue there are and how tissues together form organs and organ systems.

The cell and its parts · Substances in and out of the cell · Cell division · Four kinds of tissue · From tissue to organ system

Your skin is a multi-layered organ that protects you, senses, regulates heat and repairs itself. In this chapter you will see the layers of the skin, how hair and nails grow, how your temperature is regulated, what pigment and UV radiation do and how a wound heals.

The layers of the skin · Hair and nails · Regulating temperature · Pigment and UV · A wound heals

Your skeleton is living tissue that supports you, protects you, lets you move, stores calcium and makes blood cells. In this chapter you will see how bone is built, how it grows in length, which kinds of joint there are, how your spine is put together and how a broken bone heals.

Bone is living tissue · Growing in length · Types of joint · Spine and posture · Fractures and healing

Muscles move you, maintain your posture and produce heat. In this chapter you will see the three kinds of muscle tissue, how a muscle contracts, how muscles and bones work as levers, where the energy comes from, and how muscles adapt to training and recover from an injury.

Three kinds of muscle tissue · How a muscle contracts · Tendons, joints and levers · Energy for your muscles · Training and injuries

Your nervous system gathers information, processes it and controls your body. In this chapter you will see how a neuron makes a signal and passes it on, how the brain and spinal cord are built, how a reflex works, and how the autonomic nervous system and sleep are regulated.

Neurons and their signal · The synapse · The brain · Spinal cord and reflexes · The autonomic nervous system and sleep

Your senses convert light, sound, movement, chemicals, touch and temperature into signals for your brain. In this chapter you will see how the eye, ear, balance organ, nose, tongue and skin work, and why perception itself only happens in your brain.

The eye and vision · The ear and hearing · Balance · Smell and taste · Touch, temperature and pain

Hormones are signalling molecules that travel in your blood and control cells elsewhere in your body. In this chapter you will see how glands release their hormones and how your blood sugar, your stress response, your thyroid, your growth and puberty are controlled.

Glands and hormones · Blood sugar, insulin and diabetes · Stress, adrenaline and cortisol · The thyroid and growth · Sex hormones and puberty

Every minute your heart pumps about five litres of blood around your body. In this chapter you will see how the heart is built, how the blood travels around two circuits, and what keeps your heart healthy.

Structure of the heart · The double circulation · Heartbeat and blood pressure · Capillaries and exchange · A healthy heart

Blood is a transport system, a sticking plaster and a defending army all at once. In this chapter you will see what blood is made of, how it clots, and how your immune system recognises pathogens, remembers them and sometimes overreacts.

Blood cells and plasma · Blood clotting · Innate and adaptive immunity · Vaccines · Allergy

Every breath brings oxygen to your blood and carries carbon dioxide away. In this chapter you follow the air through your airways right into the alveoli, see how muscles and pressure differences drive breathing, and find out what asthma and smoking do to your lungs.

The airways · Alveoli and gas exchange · How breathing works · Asthma · Smoking and the lungs

What you eat first has to become small enough to get into your body. In this chapter you follow food from the mouth to the large intestine, and see how enzymes break it down, what the liver and pancreas do, what nutrients are for and what part gut bacteria play.

Mouth, stomach and intestine · Enzymes · The liver and the pancreas · Nutrients and what they do · Gut bacteria

Every day your kidneys filter far more fluid out of your blood than you ever pass as urine, and they take most of it back. In this chapter you will see how a kidney is built, how filtration and reabsorption work, how your body controls its water balance, how urination works and what happens when the kidneys work less well.

Structure of the kidney · Filtration and reabsorption · Water balance · The bladder and urination · When the kidneys work less well

How the cell membrane controls substances and voltage, how a cell harvests energy, makes proteins, divides or clears itself away, how tissues are built up under the microscope and how cells pass on signals — with, for each model, what it does and does not tell you.

Cell membrane and transport · Organelles and energy · DNA and protein synthesis · Cell cycle and apoptosis · Tissues in detail · Signal transduction

How the skin is built under the microscope, how the horny layer keeps out water and microbes, how the skin helps regulate temperature, what UV does to pigment and DNA and how a wound heals in phases — and which skin diseases you can understand from that, with what each model does and does not say.

Histology of the skin · Skin barrier and microbiome · Thermoregulation as a control loop · Pigment, UV and vitamin D · Wound healing in phases · Pathology in outline

How bone tissue is built under the microscope, how bone forms, grows and renews itself throughout life, how the skeleton takes part in calcium and phosphate homeostasis, how articular cartilage absorbs pressure and how a fracture heals — with, for each model, what it does and does not tell you.

Bone tissue · Bone formation and growth · Remodelling · Calcium and phosphate homeostasis · Joints and cartilage · Fractures and osteoporosis

How a skeletal muscle is built from tendon to sarcomere, how myosin and actin generate force, how an electrical signal leads to contraction, where the ATP comes from, how the nervous system grades force and muscle adapts, and how smooth muscle works differently — with, for each model, what it does and does not tell you.

Structure of skeletal muscle · Sliding filaments and the cross-bridge cycle · Excitation–contraction coupling · Energy systems · Fibre types, motor units and training · Smooth muscle

How a neuron generates and transmits an electrical signal, how the brain and spinal cord are organised and control movement, how the autonomic nervous system regulates the organs, and how synapses change and sleep is structured — with, for each model, what it does and does not tell us.

Resting and action potentials · Synaptic transmission · Functional anatomy of the brain · Spinal cord and motor control · The autonomic nervous system · Plasticity, memory and sleep

How the eye refracts light and the retina converts photons into an electrical signal, how hair cells measure sound and movement, how smell and taste work with receptors and codes, and how touch and pain reach the spinal cord and the brain — with, for each model, what it does and does not tell you.

Optics and accommodation · Retina and phototransduction · Hearing and the cochlea · The vestibular system · The chemical senses · Somatosensation and pain

How hormones are built and find their receptors, how the hypothalamus and pituitary control the thyroid, the adrenal gland, growth and the gonads, how a beta cell measures glucose, and how control loops with negative and sometimes positive feedback work — with, for each model, what it does and does not say.

Hormone classes and receptors · Hypothalamus, pituitary and feedback · Glucose regulation · The adrenal gland and the stress response · The thyroid and metabolism · Sex hormones and the HPG axis

How the heart generates its own rhythm, how pressure and volume change with each beat, and how the body regulates blood pressure and tissue perfusion — up to the point where things go wrong.

Conduction system and ECG · The cardiac cycle: pressure and volume · Cardiac output and Frank-Starling · Blood pressure regulation: baroreflex and RAAS · Microcirculation and Starling forces · Atherosclerosis in outline

How the bone marrow makes billions of cells every day, how a bleed stops without the blood clotting everywhere, and how innate and adaptive immunity protect together — up to the point where they do harm.

Haematopoiesis · Haemostasis and coagulation · Innate immunity · Adaptive immunity · Vaccination and immunological memory · Hypersensitivity and autoimmunity

How pressures and surface tension make the lung move, how oxygen and CO₂ cross a wafer-thin wall and travel through the blood, and how the brainstem regulates it all — up to the point where it goes wrong.

Mechanics of breathing · Gas exchange and diffusion · Oxygen transport · CO₂ and acid–base · Control of breathing · Obstructive and restrictive

How a nervous system of its own in the gut wall controls movement, how each nutrient is broken down and absorbed, what the liver, pancreas and microbiome contribute — and, in outline, where it goes wrong.

Motility and the enteric nervous system · Digestion and absorption, nutrient by nutrient · The liver: metabolism and detoxification · The exocrine pancreas · Microbiome · Pathology in outline

How a nephron filters, reabsorbs and secretes segment by segment, how the kidney dilutes or concentrates urine and keeps acid, salt and potassium in balance — and how you measure how well it works, with what each measure does and does not tell you.

The nephron · Glomerular filtration · Tubular reabsorption and secretion · Concentrating urine · Acid–base and electrolytes · Measuring kidney function