Human Body

What is the body composed of? The body has 5 levels of organization: cells, tissues, organs, organ systems, and the organism itself The cell is the basic unit of life and makes up all living things Depending on the type of organism, the cells will have different functions For example, in a single celled organism, the individual cell is responsible for capturing and releasing energy In more complex organisms, cells are specialized and perform specific jobs Red blood cells carry oxygen from the lungs throughout the body; white blood cells help fight off infection

There are between 4,000-10,000 white blood cells per microliter of blood in a normal adult body

Tissues A tissue is a group of similar cells that work together to perform a particular function The human body contains several types of tissues and they can be classified into 4 main groups according to their functions Epithelial tissue functions as a boundary covering all of the inner and outer surfaces of your body

Nerve tissue functions as a messaging system by carrying electrical impulses between your brain and the various parts of your body in response to changing conditions Muscle tissue functions in movement resulting when muscle cells contract and relax Connective tissue functions to hold parts of the body together providing support, protection, strength, padding, and insulation. Tendons and ligaments are connective tissues that hold bones and muscles together

Organs An organ is a structure that is made up 2 or more types of tissue that work together to carry out a function in the body As in cells and tissues, the structure of an organ relates to its function

Organ Systems An organ system is a group of organs that together perform a function that helps the body meet its needs for energy and materials The body is made up of many organ systems

Organisms The 5th level of organization is the organism itself.