Organs

Your body is built in levels. Cells group into tissues, tissues build organs, organs work together in organ systems, and all the systems together make an organism: you.

Level	What it is	Example
Cell	The smallest living building block	A muscle cell
Tissue	A group of similar cells doing the same job	Muscle tissue
Organ	Different tissues working together to do a job	The heart: muscle tissue, nervous tissue and connective tissue holding it together
Organ system	A group of organs working together	The circulatory system: heart, blood vessels and blood
Organism	A whole living thing	You

The map faces you, so the body’s right side is on the left of the picture: the liver is under the right ribs, the stomach under the left.

Organ	Where	Job
Brain	Inside the skull	Controls the body: thinking, memory and feelings, and the things you never think about, such as breathing
Lungs	The chest, either side of the heart	Take oxygen into the blood and let carbon dioxide out
Heart	Middle of the chest, tilted to the left	Pumps blood round the body
Liver	Under the ribs on the right	Makes bile, stores glucose and breaks down harmful substances such as alcohol
Stomach	Under the ribs on the left	Churns food and mixes it with acid and enzymes
Pancreas	Behind the stomach	Makes digestive enzymes, and insulin to control blood sugar
Small intestine	Coiled in the middle of the belly	Finishes digestion and absorbs the nutrients into the blood
Large intestine	Round the edge of the belly	Absorbs water from what is left, leaving faeces
Kidneys	At the back, either side of the backbone	Filter waste out of the blood to make urine
Bladder	Low in the belly, inside the pelvis	Stores urine
Skin	All over: the largest organ	Keeps microbes out, helps control temperature, senses touch, heat and pain

An organ system is a team of organs with one job. No system works alone: the circulatory system delivers what every other system needs, and the nervous system tells them all when to work.

Organ system	Main organs	Job
Digestive system	Mouth, oesophagus, stomach, liver, pancreas, small intestine and large intestine	Breaks food down into molecules small enough to pass into the blood, and gets rid of the rest
Circulatory system	Heart, arteries, veins, capillaries and the blood	Carries oxygen, nutrients and waste round the body in the blood
Breathing (respiratory) system	Nose, trachea, bronchi, lungs and diaphragm	Moves air in and out of the lungs, taking oxygen into the blood and carbon dioxide out
Nervous system	Brain, spinal cord, nerves and the sense organs	Senses what is happening and controls the body with fast electrical signals
Skeletal system	Bones, joints, ligaments and cartilage	Supports and protects the body, lets it move at joints and makes blood cells
Muscular system	The muscles and their tendons	Pulls on bones to move the body at its joints
Excretory (urinary) system	Kidneys, ureters, bladder and urethra	Filters waste out of the blood and removes it from the body as urine
Reproductive system	Ovaries and uterus (womb) in females, testes in males	Makes sex cells so that a new living thing can be made

Plants have organs too. Roots take in water and minerals and anchor the plant. The stem holds the plant up and carries water and food around it. Leaves make food by photosynthesis. Flowers make seeds. A leaf is an organ made of tissues, just like your stomach.

Stretch A unicellular organism such as an amoeba has no tissues or organs: one cell does everything. Blood is a tissue, not an organ, even though it is a liquid. An adult liver weighs about 1.5 kg, the heaviest organ inside the body; only the skin, on the outside, is bigger.