Not Medical Advice: Levels of Organization in the human body (smallest to largest) starts with the cells, followed by the tissues, then the organs, and ending with the organ systems.
Cells are the basic units of structure and function in the human body, as they are in all living things. Each cell carries out basic life processes that allow the body to survive. The body is composed of many different types of cells, each with its own structure and function. Some types of cells include:
- Blood cells
- Muscle cells
- Skin cells
- Nerve cells
- Glandular cells
A tissue is a group of connected cells that have a similar function. In humans, there are four basic types of tissue:
- Nervous tissue
An organ is a structure that consists of two or more types of tissues that work together to do the same job. There are almost 78 organs in a human body which vary according to their sizes, functions or actions.
Some organs in the human body include:
- Skin (largest organ with respect to its size and weight)
- Brain (primarily responsible for performing all the functions and actions of the body)
- Lungs (major organ of our respiratory system, helping us obtain oxygen and get rid of carbon dioxide)
- Heart (main organ of our body's circulatory system, pumping blood throughout the body)
- Stomach (important part of our digestive system which receives food from the esophagus)
An organ system is a group of organs that work together to carry out a complex overall function. Communication between organs and organ systems is vital, as it allows the body to adjust the function of each organ according to the needs of the whole body.
Some examples of organ systems include:
- Digestive (or gastrointestinal) system (responsible for receiving and digesting food and excreting waste)
- Cardiovascular system (responsible for pumping and circulating the blood)
- Musculoskeletal system includes the bones, muscles, ligaments, tendons, and joints, which support and move the body.
Human anatomy deals with anatomical structures of the human body, including cells, tissues, organs, and organ systems. And studying anatomy involves lots of memorization. Check out some tips that will help make learning and memorizing body structures easier at About.com.