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How do tissues combine to form an organ?

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Vintage anatomy chart showing front and back views of the human skeletal system and muscular system, with detailed illustrations of bones and muscles. — human body Vintage anatomy charts of the human body showing the skeletal and muscle systems.

In the human body, an organ is formed when different types of tissues aggregate to constitute a distinct structural and functional unit.1

The human body is composed of four basic classes of tissue, which work together to create these complex structures:
* Epithelial tissues: Cover the body’s surface and line internal organs, cavities, and passageways.1
* Muscle tissues: Provide the ability to contract, forming the musculature and surrounding the walls of many internal organs.12
* Nerve tissues: Conduct electrical impulses to coordinate bodily functions.12
* Connective tissues: Bind various body structures together, provide internal support, and maintain the form of organs.31

For example, the heart is an organ composed of all four of these tissue types, working in unison to pump blood throughout the body. These organs do not function in isolation; they are grouped into organ systems to perform life-sustaining functions.14