1The human body is one of the most complex and remarkable structures in the natural world. Made up of trillions of cells, it is organised into tissues, organs and organ systems, each working together to keep you alive and functioning. From the moment you are born until the end of your life, your body is constantly working, even while you sleep.
2The skeletal system provides the body with its structure and support. Adults have 206 bones, which protect vital organs, allow movement and produce blood cells in the bone marrow. The skeletal system works closely with the muscular system, as muscles attached to bones contract and relax to create movement.
3The circulatory system is responsible for transporting blood, oxygen and nutrients around the body. At its centre is the heart, a muscular organ that beats approximately 100,000 times a day, pumping blood through a vast network of arteries, veins and capillaries. If all the blood vessels in a human body were laid end to end, they would stretch for approximately 100,000 kilometres.
4The respiratory system brings oxygen into the body and removes carbon dioxide. When you breathe in, your diaphragm contracts and your lungs expand to draw in air. Oxygen passes from the lungs into the bloodstream, while carbon dioxide is expelled with each breath out.
5The brain is the control centre of the entire body. It receives and processes information from the senses, coordinates movement and controls functions such as breathing, digestion and heartbeat. The human brain contains approximately 86 billion neurons, each forming connections with thousands of others to create an extraordinarily complex network of communication.
Match each word to its correct meaning.
Blood travels through away from the heart. The contracts when you breathe in. The lungs pass into the bloodstream. The brain contains 86 billion .