Tissue is a group of cells that have similar structure and function together as a unit. The intercellular matrix, which is a nonliving material, fills the spaces between the cells. There are four main types of tissues in the body: epithelial, connective, muscle, and nervous, each designed for specific functions. The intercellular matrix may contain special substances such as salts and fibers that are unique to a specific tissue and gives that tissue distinctive characteristics.
The concept of tissues can be traced back to 1801 when it was introduced by Xavier Bichat, a French anatomist and pathologist. Tissues are absent from unicellular organisms, but multicellular animals and plants that are more advanced have specialized tissues that can organize and regulate an organism’s response to its environment.
In animals, there are four types of tissues: muscle tissue, connective tissue, nervous tissue, and epithelial tissue. Muscle tissue includes cardiac, skeletal, and smooth muscle tissues, while connective tissue includes cartilage, blood, and bone. Nerve tissue is made up of nerve cells (neurons) and is used to carry "messages" to and from various parts of the body. Epithelial tissue provides a covering, such as the skin and the linings of the various passages inside the body.
In plants, there are three types of tissues: dermal tissues, ground tissues, and vascular tissues. Dermal tissues include epidermal cells, stomata, and trichomes, while ground tissues include collenchyma, parenchyma, and sclerenchyma. Vascular tissue includes vessel elements, tracheids, companion cells, and sieve tubes.
The use of tissue or specimens in research is vital for medical science to advance. The study of tissues is known as histology or, in connection with disease, as histopathology).
