5.2: Epithelial Tissues
- Page ID
- 53571
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Epithelial tissues are found on the surfaces of all organs inside and out of the human body and as such, epithelial tissues have one edge not connected to other cells, the apical surface. The other end of an epithelial tissue (the basal surface) is attached to a basement membrane that is partly produced by the epithelial cells. Underlying the basement membrane are connective tissues. Carefully examine the diagram below to become familiar with recognizing different types of epithelial tissues and their positions in relationship to the basement membrane and the underlying connective tissues. Epithelial tissues do not contain blood vessels and as such are avascular. Connective tissues are usually highly vascular and so the nearby connective tissue provides essential nutrients (from the blood) to the epithelial tissue.
Epithelial tissues are described using a 2-word naming system:
- First word: simple, stratified, or pseudostratified (these terms indicate the number of cell layers - see figure below)
- Second word: squamous, cuboidal, columnar, or transitional (these terms indicates the cell shape - see figure below)
For example, examining the diagram below, the tissue shown in the bottom left corner would be called "stratified squamous" since the cells are flat (squamous) and there are more than two cell layers (stratified). The top second from the left on the diagram would be called, "simple cuboidal" since there is one cell layer (simple) and the cells are cube-shaped (cuboidal). There are some epithelial tissues that look like they are stratified, but they are in fact a single layer of cells - these tissues are called pseudostratified or "false/fake stratified." The tissue in the figure below on the top right is therefore called, "pseudostratified columnar." Simple epithelial tissues are only one cell layer thick to enable absorption, diffusion, or secretion of materials across the tissue. Stratified epithelial tissues have multiple cell layers primarily to protect the tissues underlying them.
Carefully examine the tables showing examples of different types of epithelial tissues and examples of where each type may be found:
Simple Epithelial Tissues
|
Simple Epithelial Tissues |
Examples of Where they are Found |
|---|---|
|
simple squamous
|
|
|
simple cuboidal
|
|
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simple columnar
|
|
Pseudostratified Epithelial Tissue
| Pseudostratified Epithelial Tissue |
Examples of Where it is Found |
|---|---|
|
pseudostratified columnar |