Background Facts

Levels of Organization

What are the levels of structural organization in vertebrate animals, including humans?

Every vertebrate animal has four major levels of hierarchical organization: cell, tissue, organ, and organ system. Each level in the hierarchy is of increasing complexity, and all organ systems work together to maintain life.

Cells in the human body organize themselves into increasingly complex structures and systems. (From Premkumar K. The Massage Connection Anatomy and Physiology. Baltimore: Lippincott, Williams & Wilkins, 2004.)

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