Body Tissues

After you have completed this section of the chapter, you should be able to meet the following objectives:

♦ Explain the process of cell differentiation in terms of
development of organ systems in the embryo and the
continued regeneration of tissues in postnatal life

♦ Explain the function of stem cells

♦ Describe the characteristics of the four different tissue types

♦ Explain the function of intercellular adhesions
and junctions

♦ Characterize the composition and functions of the
extracellular components of tissue

In the preceding sections, we discussed the individual cell, its metabolic processes, and mechanisms of commu­nication and replication. Although cells are similar, their structure and function vary according to the special needs of the body. For example, muscle cells perform different functions from skin cells or nerve cells. Groups of cells that are closely associated in structure and have common or similar functions are called tissues. Four categories of tissue exist: (1) epithelium, (2) connective (supportive) tissue, (3) muscle, and (4) nerve. These tissues do not exist in isolated units, but in association with each other and in variable proportions, forming different structures and organs. This section provides a brief overview of the cells in each of these four tissue types, the structures that hold these cells together, and the extracellular matrix in which they live.