A tissue is a group of cells that are integrated and have a common structure and function. The term tissue comes from the Latin word meaning "weave." This is reflective of the fact that tissues are often held together by an extracellular matrix that coats and weaves the cells together. In vertebrates, there are four main categories of tissue including connective tissue, epithelial tissue, nervous tissue, and muscle tissue.

Connective tissues function mainly to bind and support other tissues and organs. They are composed of a relatively small number of cells scattered throughout an extracellular matrix. Typically, this matrix is composed of some type of protein fiber embedded in a gelatinous substance. The main vertebrate connective tissues are loose connective tissue, adipose tissue, fibrous connective tissue, cartilage, blood and bone. Loose connective tissue is the most abundant type and it holds organs in place. It is made up...