Epithelial Tissues

Epithelial tissues are characterized by tightly packed cells with little or no intercellular material. Epithelial tissues are always attached to underlying connective tissue by a basement membrane (Figure 5.1) which acts like glue. Epithelial tissues cover the body and line the cavities of the body. Additionally, epithelial tissues form the secretory portions of glands.

There are eight types of epithelial tissues. These types can be determined microscopically by first noting how many layers of cells are in the tissue and secondly the type of cells in the superficial layer.

If there is a single layer of cells, the tissue is simple epithelium. If there is more than one layer of cells, the tissue is stratified epithelium.

The three types of cells found in epithelial tissues are: squamous, cuboidal, and columnar. Squamous cells are fiat and irregularly shaped while cuboidal cells have basically the same width, length, and height. These cells look like cubes with rounded corners.

Columnar cells are characterized by being taller than they are wide. They show the most variation of all epithelial cells. Columnar cells can be ciliated or unciliated. Some columnar cells have many microscopic folds of their cell membranes called microvilli. A goblet cell is a special columnar cell shaped like a goblet. Goblet cells secrete mucus.

An epithelial tissue takes its name from the shape of the cells in the superficial layer regardless of the shape of the cells in other layers.

By combining the two criteria of epithelial tissues, we have six categories: simple squamous, simple cuboidal, simple columnar, stratified squamous, stratified cuboidal, and stratified columnar. The two remaining epithelial tissues are special cases.

Pseudostratified (pseudo = Gr. false) epithelium is in reality a simple tissue. That is, it is composed of one layer. However, because the cells of this tissue are different in size they give the appearance of being stratified. Pseudostratified tissue can be identified microscopically by the presence of various sized cells (cuboidal and columnar) all of which contact the basement membrane.

The second special epithelial tissue is transitional. Transitional epithelium lines the urinary bladder. It looks like stratified cuboidal epithelium except that the uppermost cells have a free, rounded appearance.

Exercise 5.1

Label the drawings in Figure 5.1 with the correct names of the tissues.

Exercise 5.2

Fill in the chart below with the appropriate terms. Epithelial Tissues

(one layer) (more than one layer)

Which cells can be ciliated?

Figure 5.1 Epithelial Tissues

Cilia Goblet cell Pseudostratified, ciliated Simple columnar, ciliated Simple columnar, unciliated Simple cuboidal Simple squamous Stratified columnar Stratified cuboidal Stratified squamous Transitional

Examine and sketch the following tissues as seen with a microscope: simple squamous, stratified squamous, simple cuboidal (kidney tubules), simple columnar (intestinal lining), and transitional (urinary bladder). As you examine the tissues, ask yourself these questions:

1. How many layers of cells are there in the epithelium?

2. What is the shape of the cells in the superficial layer?

3. If there are columnar cells, do they have cilia? Do they have microvilli?

Be able to identify each of these tissues from a drawing, a description, and microscopically.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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