2.2 Epithelial Tissues

Epithelial tissue is tissue that covers surfaces and lines cavities. Here, it may protect, absorb, and/or secrete. Epithelial tissue covers the outer surface of the body. It lines the intestines, the lungs, and other hollow organs.

TYPES OF EPITHELIAL CELLS (BY SHAPE)

Figure 2-1 illustrates the basic types of epithelial cells by shape. The three basic shapes are squamous (flat), cuboidal (cubes), and columnar (columns).

Figure 2-1. Epithelial cells.

TYPES OF EPITHELIAL TISSUES

a. Layers. In epithelial tissues, the cells are in single or multiple layers. If there is only one layer, the tissue is called a simple epithelium. If there is more than one layer, the tissue is called a stratified epithelium. See figure 2-2.

Figure 2-2. Types of epithelial tissues.

Epithelial tissues are named by the number of layers and the type of cell in its outermost layer. For example, if there are several layers and if the outermost layer consists of squamous (flat) cells, then the tissue is called a stratified squamous epithelium.

Examples of Epithelial Tissues.

A simple squamous epithelium called endothelium lines the heart and blood vessels.

As serous membranes, simple squamous epithelial tissue lines the cavities of the abdomen (peritoneal lining) and the chest (pleural lining). Serous membranes are membranes which secrete a lubricating fluid.

Epithelial tissue forms the secretory part of glands and also parts of the various sense organs.

According to its location, epithelial tissue has different functions. As the skin, epithelial tissue protects the tissues beneath. In the small intestines, the epithelial tissue absorbs. In the lungs, epithelial tissue is a membrane through which the gases pass easily. In the glands, epithelial tissue secretes.