Organ Systems and Their Functions in the Human Body
The human body has 11 organ systems: integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic and immune, respiratory, digestive, urinary and reproductive. Each is a group of organs that work together to do one major job, and all of them depend on each other.
What are the levels of organisation in the body?
Living things are built in steps, each made from the one before:
- Cell: the basic unit of life, such as a muscle cell.
- Tissue: similar cells working together, such as muscle tissue.
- Organ: different tissues forming one structure, such as the heart.
- Organ system: several organs cooperating, such as the cardiovascular system.
- Organism: all the systems together, which is you.
An organ is a structure made of at least two tissues that does a specific job. The stomach, for example, contains muscle, glandular and nervous tissue.
How many organ systems are in the human body?
Most textbooks list 11 organ systems. Some sources combine or split a few, but this is the standard answer.
| Organ system | Main organs | Function |
|---|---|---|
| Integumentary | Skin, hair, nails | Protects, controls temperature, senses touch |
| Skeletal | Bones, joints, cartilage | Supports, protects organs, makes blood cells |
| Muscular | Skeletal, smooth and cardiac muscle | Moves the body and moves substances inside it |
| Nervous | Brain, spinal cord, nerves | Sends fast electrical signals to control the body |
| Endocrine | Pituitary, thyroid, pancreas, adrenals | Releases hormones that control growth and metabolism |
| Cardiovascular | Heart, blood vessels | Pumps blood to carry oxygen and nutrients |
| Lymphatic and immune | Lymph nodes, spleen, thymus | Fights infection and drains tissue fluid |
| Respiratory | Lungs, airways | Takes in oxygen and removes carbon dioxide |
| Digestive | Stomach, intestines, liver | Breaks down food and absorbs nutrients |
| Urinary | Kidneys, bladder | Filters blood and removes waste as urine |
| Reproductive | Ovaries, testes and related organs | Makes gametes and allows reproduction |
Some facts that make each system concrete
- The skin is the body's largest organ.
- An adult skeleton has 206 bones, and the body has more than 600 skeletal muscles.
- The heart beats about 100,000 times a day, pumping blood round roughly 100,000 km of blood vessels (see how blood works).
- The small intestine is about 6 metres long, which gives food a huge surface to be absorbed through.
- The kidneys filter the blood and produce about 1.5 litres of urine a day.
- Adults breathe about 12 to 20 times a minute at rest (how the respiratory system works).
Organ system examples: how they work together
Organ systems are linked, and one action involves several. Take running for a bus:
- The nervous system decides to move and sends signals to the legs.
- The muscular and skeletal systems contract and lever your legs.
- The cardiovascular system speeds up so blood delivers more oxygen.
- The respiratory system breathes faster to supply that oxygen and remove carbon dioxide.
- The integumentary system sweats to lose the extra heat.
- The endocrine system releases adrenaline to keep it all going.
Five or six systems respond to one decision, which is why a problem in one often shows up in another.
What is the difference between an organ and an organ system?
An organ is one structure doing a specific job, like the stomach. An organ system is a team of organs. The stomach, liver, pancreas and intestines are all organs, and together they make up the digestive system.
Which organ systems work together to deliver oxygen?
The respiratory system takes oxygen in at the lungs, and the cardiovascular system carries it round the body in the blood. The digestive system adds the nutrients that the cells use with the oxygen. Together, they supply every cell with what it needs for respiration.
Common mistakes
- Calling the circulatory system and the cardiovascular system different things. Many courses use both names for blood, heart and vessels.
- Listing an organ as a system: the heart is an organ, not an organ system.
- Forgetting that one organ can belong to more than one system. The pancreas is in both the digestive and the endocrine systems.
- Mixing up the nervous system (fast, electrical) with the endocrine system (slower, chemical).
Frequently asked questions
What are the 11 organ systems?
They are the integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic and immune, respiratory, digestive, urinary and reproductive systems. Each carries out a major job and depends on the others.
What is the function of an organ system?
An organ system carries out one major body function by combining the work of several organs. For example, the digestive system breaks down food and absorbs nutrients using the stomach, intestines, liver and pancreas.
Which organ system controls all the others?
The nervous and endocrine systems coordinate the rest. The nervous system uses fast electrical signals, and the endocrine system uses hormones released into the blood, which act more slowly but last longer.
Is the brain an organ or an organ system?
The brain is an organ. It belongs to the nervous system, together with the spinal cord and nerves.
Try it yourself
Explore two systems in 3D: follow blood round the body in Heart & Circulation, then look at signals in Brain & Neurons. For each one, list which other organ systems it depends on.
See it for yourself, in 3D and free.
Try it in the Heart & Circulation