Adrianne has a master's degree in cancer biology and has taught high school and college biology.
Have you spent any time thinking about the different parts of your body and what they are made of? You know that different parts of your body have different functions, so you probably already know they aren't made of the exact same thing.
You know some parts of your body stretch, while others don't. You know that some parts of your body secrete things, while others absorb. You probably even know that some parts of your body are there for protection, while other parts are there to nourish the body. Well, that is a great start to understanding the different types of tissues that make up the organs of your body.
We are going to spend some time learning about epithelial tissues. This is the tissue that covers and lines your body and internal organs. This tissue has one side that is open to an internal or external space, and the other side is attached to connective tissue.
The main functions for epithelial tissues are secretion, absorption, excretion and protection. Epithelial tissues also don't have blood vessels and tend to divide quicker than other tissue types. There are several types of epithelial tissues, and they are grouped based on the appearance and organization of cells in the tissue. Let's look at the different types of epithelial tissues now.
Simple Epithelial Tissues
The simple epithelial tissues are considered simple because they only contain one layer of cells and all cells have the same shape.
Simple squamous epithelium tissues have one layer of flattened cells that allow substances to pass through them. The main functions for this tissue type are diffusion, osmosis and filtration. Simple squamous tissue is found in areas where these functions are needed, such as the air sacs of the lungs and the linings of the blood and lymph vessels.
Simple columnar epithelium tissues have one layer of cells shaped like columns. The cells in this tissue have their nuclei close to the surface attached to connective tissue and have goblet cells on the free surface, which secrete mucus. The functions of this tissue type are protection, secretion and absorption, and it is located in the linings of the stomach, uterus and intestines.
The last one in this category is simple cuboidal epithelium tissue, which has one layer of cube-shaped cells that allow for it to carry out the functions of secretion and absorption. Simple cuboidal tissue is found covering the ovaries and in the linings of the kidneys to secrete and absorb. It is also found in clusters in glands to secrete.
Stratified Epithelial Tissues
The stratified epithelial tissues have multiple layers of cells with differing shapes. The names for stratified epithelial tissues are determined based on the type of cells on the outer surface.
Stratified squamous epithelium include a layer of flattened squamous cells on the surface, and they function to protect the areas where they are located. You can find this tissue type in the lining of the beginning of the GI tract, such as the mouth and esophagus, and on the skin's surface.
Cube-shaped cells can be found on the surface of stratified cuboidal epithelium. This is the least common of the epithelial tissues. The tissue is found in the ducts of exocrine glands to include the reproductive organs. The function of stratified cuboidal epithelium is to protect the largest ducts of the exocrine glands.
Stratified columnar epithelium has layers of columnar cells that may have cilia on them. The functions of stratified columnar epithelium are protection and secretion. This tissue is found in parts of the throat, urethra, and ducts of the mammary and salivary glands.
Other Epithelial Tissues
There are two types of epithelial tissues that don't fit into either of the other two categories of epithelial tissues. The first one is transitional epithelium. Transitional epithelium contains six layers of various shaped cells and changes appearance based on if it is stretched or relaxed. This tissue is able to expand as needed and is found lining the organs throughout the urinary tract.
The other irregular type of epithelium is pseudostratified columnar epithelium. This type of tissue isn't truly stratified since it doesn't have more than one layer. The cells are oriented in opposite directions, so it looks like more than one layer. Most of this tissue has cilia on the surface and functions to secrete and propel mucus. This aids in protection for the organs of the upper respiratory tract. It is also found in some tubules and organs of the male reproductive tract. The tissue that appears here doesn't contain cilia and functions to secrete.
You should now be aware there are different types of epithelial tissue that line the body and internal organs. All epithelial tissue has one surface attached to connective tissue, while the other surface faces an opening to the outside or an internal opening. The simple epithelial tissues all have one layer of the same type of cell. The functions of epithelial tissues include protection, absorption, secretion and excretion.
The three types include simple squamous, simple cuboidal and simple columnar. Stratified epithelial tissues contain more than one layer and type of cell. The different types of stratified epithelia are stratified squamous, stratified columnar and stratified cuboidal. The other two types of epithelial tissues are pseudostratified, which have cells going in opposite directions, and transitional, which stretch as needed.
Study this video lesson, then use your enhanced knowledge to accomplish the following:
- Recognize the structure and function of the three types of simple epithelial tissue and the three types of stratified epithelial tissue
- Identify examples of each of the above types of epithelium
- Lay out the structure, function and location of transitional and pseudostratified epithelial tissues
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