Our bodies are organized at many different levels. The levels of organization of living things, from smallest to largest, are
- Atoms, the smallest functional units of matter.
- Molecules, active chemicals.
- Organelles, specialized structures within a cell.
- Cells, the smallest living units.
- Tissues, a group of similar cells that work together.
- Organs, two or more tissue types working together.
- Organ systems, two or more organs working together.
- Organism, a single individual, including all of the above
The human body is divided into 11 interconnected organ systems. All organ systems work together, and many organs function in more than 1 organ system
- The Integumentary System: includes the skin & derived structures, it protects internal organs & helps maintain body temperature.
- The Skeletal System: includes the bones & joints, it provides support & protection to internal organs.
- The Muscular System: includes skeletal muscle and it provides movement.
- The Nervous System: includes the brain, spinal cord, and nerves. It provides regulation of body functions & sensory perception.
- The Endocrine System: includes hormone-producing cells & glands. It regulates homeostasis, growth & development.
- The Cardiovascular System: includes blood, heart, & blood vessels. It is responsible for delivery of oxygen & nutrients to the tissues.
- The Lymphatics & Immune System: includes lymphatic vessels & fluid. It is involved in the defense against infection.
- The Respiratory System: includes lungs & airways. It is involved in the absorption of oxygen & release of carbon dioxide.
- The Digestive System: includes organs of the gastrointestinal tract. It is responsible for the absorption of nutrients
- The Urinary System: includes the kidneys, ureters, and bladder. It is responsible for electrolyte balance & waste removal.
- The Reproductive System: includes the reproductive organs in males and females. It controls the biological process by which new individuals are produced