Mammalian tissues

General

The basic unit of the mammalian body is the cell. We now know of what a single cell consists, as well as the basic functions a living cell can perform. Each type of cell or group of cells is able to perform a specific function or functions, in other words they differentiate. Differentiation results in cells becoming functionally specialised. Cells are also the first level of organisation in living organisms.

Such a group of cells, within which all cells have more or less the same structure and function, is called a tissue. Tissues are the second level of organisation. Muscle, bone and blood are examples of animal tissues.

A group of different tissues, each with its own function, but working together for a major function, is called an organ. The stomach, the heart, the liver are examples of organs. Organs are the third level of organisation.

In some cases there is a group of organs, each with its own specific function, but which work together to perform an overall common function. This is called a system. The digestive system is an example of a system. Systems are the fourth level of organisation.

Tissue - a definition

A tissue is usually defined as a group of cells, more or less similar in structure and function, with their intercellular substance, which perform a common group function.

In this section we shall concern ourselves mainly with the second level of organisation, i.e. the tissue level. There are four main groups of specialised tissue making up the body of a mammal. They are: