| In an average lifetime the heart beats over 3 billion times | Circulation |
| Red blood cells carry oxygen to every cell and remove carbon dioxide | |
| Blood vessels help to control our bodies' temperature | |
| If stretched out, your blood vessels would extend almost 100,000 km | |
| Blood is made from red cells, white cells, plasma and platelets | |
| Our bodies produce between 1 and 2 litres of saliva every day | Digestion |
| Food can go through the digestive system if you are upside-down | |
| The small intestine is 7 metres long. The large is just 1.5 metres | |
| Our stomachs contain hydrochloric acid | |
| We burp to release air that has been accidentally swallowed | |
| The glands that produce hormones make up the endocrine system | Hormones |
| The hypothalamus gland regulates our hunger and thirst | |
| Our bodies create and use more than 50 different hormones | |
| The pituitary gland is one of the most important, but it's the size of a pea | |
| The pancreas releases insulin and glucagon to regulate blood sugar | |
| The immune system protects us from bacteria and viruses | Immunity |
| There are 5 types of white blood cells which fight pathogens | |
| Fevers are caused by our bodies as a way to fight pathogens | |
| Allergies are caused by our immune system reacting to harmless things | |
| Sleep is important for a healthy immune system | |
| There are over 650 skeletal muscles in the body and billions of others | Muscles |
| The largest muscle in the body is the gluteus maximus in your bottom | |
| Size for size, the strongest muscle is the masseter in the jaw | |
| Most of the heat produced in your body comes from contracting muscles | |
| Many muscles, like the triceps and biceps, work in pairs | |
| There are 4 different kinds of nerve cell in the nervous system | Nerves |
| The central nervous system is the brain and the spinal cord | |
| All other nerves are part of the peripheral nervous system | |
| The brain uses more energy than any other organ | |
| Neurons can’t replace themselves so nerve damage is often permanent | |
| Our kidneys filter toxins from our blood, converting them to urine | Renal |
| Our bladders can hold up to 800 ml of urine - about 4 cups full | |
| Urine is 95% water, 2.5% urea, and 2.5% minerals and enzymes | |
| The kidneys and bladder are linked by thin tubes called ureters | |
| Kidney stones are caused by minerals forming crystals | |
| Our lungs can hold up to 6 litres of air | Respiration |
| The left lung is smaller than the right one to make room for the heart | |
| If the lungs were unfolded they’d be roughly the size of a tennis court | |
| Our lungs contain 3-5 million air sacs called alveoli | |
| Our lungs are protected by the epiglottis which covers the trachea | |
| There are 206 bones in an adult skeleton | Skeleton |
| The smallest bone in the body is in your ear | |
| The femur, or thigh bone, is the longest bone in your body | |
| More than half your bones are in your hands and feet | |
| The hyoid bone in the throat is the only bone not connected to another | |
| The average person’s skin covers an area of 2 square metres | Skin |
| A square centimetre of skin contains 6 million skin cells | |
| The skin on your soles is 1.4 mm thick. On your eyelids it's 0.2 mm | |
| Your skin sheds 30-40,000 dead cells an hour | |
| Up to 1,000 species of bacteria live on our skin | |
