2-18. EPITHELIAL CELL TYPES
By observing microscopic preparations of epithelial tissues, one can classify the
cells of epithelial tissues into three general types: columnar, cuboidal, and flat
2-19. EPITHELIAL TISSUE TYPES
If an epithelial tissue consists of a single layer of cells, it is called a simple
epithelial tissue. When there are several layers of cells, it is called a stratified epithelial
tissue. In both cases, the epithelial tissue is further identified by the type of epithelial
cell that forms the outermost layer of the tissue. For example, the outer layer
(epidermis) of the skin is a stratified squamous epithelium; squamous cells form the
outermost of many layers.
2-20. LINING OF SEROUS CAVITIES
The many serous cavities of the body are lined with a simple squamous
epithelium. This epithelial tissue also secretes a serous fluid to act as a lubricant,
reducing frictional forces of organs moving against each other. An example is the outer
surfaces of the lungs, which move on the inside of the chest wall (within the pleural
cavity) during breathing.
2-21. OUTER SURFACE OF THE BODY
The outer layer of the skin is a stratified squamous epithelium. In it, there are
many layers of cells. The outermost layers consist of squamous, or flat, cells.
2-22. SECRETORY PROCESSES
Secretory epithelial cells, such as those in various glands, have a well-developed
Golgi complex. In one type of secretory cells, the secretions are passed through the
cell membrane. In another type of secretory cells, those of the sebaceous glands, a
portion of the cell containing the secretion is sloughed off from the cell.