|
|
|
TRY OUT YOUR SKILLS WITH THIS QUIZ! Updated - 02/21/2017
Check Out the Slide Show for Extra Practice!
Tissues
The word "tissue" is derived from the word meaning "woven". This indicates the intimate structural and functional relationship that exists between the cells in a given tissue. Tissues are made up of a group of cells that have similar origins and serve a specific function in the body. Cells in a tissue are physically arranged in such a way to serve their unique purpose. This is another illustration of the complementarity between structure and function.
Although there are many types of cells in the human body, they are all organized into four broad categories of tissues: epithelial, connective, muscle, and nervous. Each tissue type has a unique physical structure that allows it to serve specific functions in your body. Many diseases become evident at the microscopic level. The field of histology specializes in detecting and analyzing the fine microscopic anatomy of tissues, for diagnostic purposes.
The Four Tissue Types
Epithelial Tissue
Beauty That is More Than Skin Deep
Epithelial cells line your internal and external surfaces, your cavity linings and most of your organs. These tissues are selectively permeable which allows them to carry out different functions that can include absorption, filtration and secretion. For example, the epithelium that lines your small intestines allows for nutrients to be absorbed by the processes of diffusion and active transport and the epithelium that lines your kidneys acts to filter out urinary waste.
Most of your epithelium is considered "epithelium proper", which refers to epithelium that lines your organs, your body cavities and all of your body's inner and outer surfaces. The main function of epithelium proper is protection.
You also have glandular epithelium that forms most of your body's glands. Glandular epithelium acts to secrete hormones for your endocrine system.
GIF Animation courtesy of gifsoup.com/view/5132402/skin-anatomy.html
The Characteristics of Epithelial Tissue
1. Cellularity - Epithelial tissue is made up of tightly packed epithelial cells that are connected to one another to form sheets.
2. Special Connections Between Cells -
- Tight junctions are integral proteins that fuse adjacent cells together to create a continuous sheet of cells that prevents molecules from passing through the intercellular space.
- Desmosomes are essentially internal tension-reducing networks of fibers that anchor adjacent cell to each other and are specially suited to resist mechanical stress.
- Gap junction s - Communicating junctions that allow ions and small molecules to pass for cell-to-cell communication
2. Polarity - A cell is considered 'polar' when one end is different from the other end. Epithelial cells are 'polar', because they have an 'upper' and an 'lower' portion. The top of the epithelial cell is called the apical side. The apical side usually has cilia or microvilli which act to move extracellular substances along. The bottom portion of epithelial tissue is called the basal side. The basal side of the tissue is connected to a basal membrane.The basement membrane is composed of collagen fibers and it function to connect your epithelial tissue to the underlying connective tissue.
3. Avascular, but Innervated- Your epithelium does not have its own blood supply, so it must get its nutrients from the nearby connective tissue. Your nervous system, however, does connect to the epithelial cells.
4. Supported by connective tissue - As previously stated, the bottom portion of epithelial tissue is called the basal side. The basal side of the tissue is connected to a basal membrane.The basement membrane is composed of collagen fibers and it function to connect your epithelial tissue to the underlying connective tissue.
5. High regenerative capacity–Epithelial cells can be replaced fairly rapidly to replaces old or damaged cells. This is an important property for wound repair.
How Are Different Epithelial Types Named?
What's in a name?
Epithelial tissue has a first name and a last name, so to speak. Epithelial tissue is named according ts layering first, followed by the shape of the epithelial cells that make up that layer.
The first name = LAYERING
Epithelial tissue is composed of one or more cell layers. When the tissue is composed of only one layer we refer to the tissue as being "simple". When the epithelial tissue is composed of two or more layers, it is referred to as "stratified". The word "stratified" literally means "layered", which also makes sense.
The last name = SHAPE
Epithelial tissue can be form from epithelial cells that have varies shapes. The last name of the tissue describe the appearance of the cells that make up the tissue.
The first name = LAYERING
Epithelial tissue is composed of one or more cell layers. When the tissue is composed of only one layer we refer to the tissue as being "simple". When the epithelial tissue is composed of two or more layers, it is referred to as "stratified". The word "stratified" literally means "layered", which also makes sense.
The last name = SHAPE
Epithelial tissue can be form from epithelial cells that have varies shapes. The last name of the tissue describe the appearance of the cells that make up the tissue.
There are three principal shapes of epithelial cell: squamous, columnar, and cuboidal.
Squamous
|
Cuboidal
|
Columnar
|
When we name tissues, we begin with the layering reference, followed by the shape reference. For example, a single layer of squamous epithelium is called, "simple squamous epithelium". A single layer of columnar epithelium is called, "simple columnar epithelium". And, as you would expect, a single layer of cuboidal epithelium would be called "simple cuboidal epithelium".
Simple Squamous Epithelial Tissue
Epithelial cells that appear flat, are called squamous epithelial cells. A tissue that is made up of squamous epithelial cells is called squamous epithelial tissue. If the squamous epithelial tissue has only one layer, we call it simple squamous epithelial tissue. If the squamous epithelial tissue has more than one layer of squamous epithelial cells, it is called stratified squamous epithelial tissue.
The terminology used for the shape of epithelial tissues is easier to remember than a lot of other terms thrown at you in anatomy class. For once, the vocabulary matches the tissue's appearance. For example, the word "squamous" means "covered in scales".
Squamous epithelium gets its name from its "scale-like" appearance. You could also think of squamous epithelium as appearing "squished", "squashed" or flattened. In addition, the nuclei of squamous epithelial cells are flattened as well. The nuclei of squamous cells tend to take up a lot of nuclear stain, so they will appear relatively dark. Squamous cells are flat.
Squamous epithelium gets its name from its "scale-like" appearance. You could also think of squamous epithelium as appearing "squished", "squashed" or flattened. In addition, the nuclei of squamous epithelial cells are flattened as well. The nuclei of squamous cells tend to take up a lot of nuclear stain, so they will appear relatively dark. Squamous cells are flat.
The main function of simple squamous epithelial tissue is to allow diffusion or filtration. For example, the alveolar sacs of the lungs are lined with simple squamous epithelial tissue that allows for the diffusion of gases between nearby blood vessels (specifically capillaries) and the lungs. Simple squamous epithelial tissue also lines your heart, your blood vessels and your lymphatic vessels. All of these areas depend upon diffusion of gases for proper functioning.
The main function of simple squamous epithelial tissue is to allow diffusion or filtration. For example, the alveolar sacs of the lungs are lined with simple squamous epithelial tissue that allows for the diffusion of gases between nearby blood vessels (specifically capillaries) and the lungs. Simple squamous epithelial tissue also lines your heart, your blood vessels and your lymphatic vessels. All of these areas depend upon diffusion of gases for proper functioning.
Slides of Simple Squamous Epithelium
Know THIS slide for the practical exam!
What |
Where |
Function |
tips |
Simple Squamous Epithlium |
Alveoli Sacs in Lungs and Blood Vessels |
Allow diffusion of gasses |
Separated Cells look like sunny-side up fried egg |
Simple Cuboidal Epithelial Tissue
Simple cuboidal epithelium is found in organs that are specialized for secretion, such as salivary glands and thyroid follicles, and those that are specialized for diffusion, such as the kidney tubules. As its name implies, this tissue consists of a single layer of cuboidal cells on the basement membrane.
Simple Cuboidal Epithelium - appears as a set of somewhat organized "cubes". Cuboidal cells are seen packed more tightly together in tissues than squamous cells. The nuclei of cuboidal epithelial cells usually appear round and are located at the center of the cell.
Simple cuboidal epithelium is found in organs that are specialized for secretion, such as salivary glands and thyroid follicles, and those that are specialized for diffusion, such as the kidney tubules. The main function of simple cuboidal cells in glands is secretion and absorption. The main function in the kidney tubules is diffusion. The slide we have for the practical are from the kidney tubules.
Slides of simple cuboidal epitheliual tissue taken from kidney tubules. This accounts for the circular arrangement of the cells. The simple cuboidal epithelial tissue appears as a single layer of cube-like cells. The nuclei are relatively large, round and centrally located within the cuboidal cells.
Slides of Simple Cuboidal Epithelial Tissue
(Kidney Tubules)
(Kidney Tubules)
Know THIS slide for the practical exam!
|
|
What |
Where |
Function |
Tips |
Simple Cuboidal Epithelium |
Glands and Kidney Tubules |
Secreteion in Gland, Absorption in Kidney Tubules |
Single layer of cube-shaped cells arranged in a circle (since this slide is from the kidney tubules). Nuclei are very round and centered in each cell. |
Simple Columnar Epithelial Tissue
Columnar epithelium looks long and cylindrical, kind of like "columns". Even the nuclei of columnar cells appear elongated into an ellipse. The nuclei of columnar epithelial cells are oriented toward the bottom (or basal side) of the cell (closer to the basement membrane).
Columnar cells are specialized for absorption and secretion. They are able to secrete mucus, enzymes, and other substances the body needs. Columnar epithelial tissue is found in our stomach lining where they create and secrete mucus.
This function requires the cell to have a lot of machinery, so the columnar cells have to be large.
Depending on the location of the tissue, some simple columnar epithelia may contain columnar cells that have cilia at their apical surfaces and may contain goblet cells.
CILIA - The cilia move mucus and other substances along a path. These cells can be found in the bronchial mucosa, which is part of the respiratory system where they function to prevent mucus from building up and blocking the airways. The bronchial mucosa also contains goblet cells which function to secrete mucus.
Slides of Simple Columnar Epithelium
Know THIS slide for the practical exam!
|
|
Stratified Squamous Epithelial Tissue
If the squamous epithelial tissue has more than one layer of squamous epithelial cells, it is called stratified squamous epithelial tissue.
Stratified squamous epithelium is found in areas of your body that experience a lot of "wear and tear" . These vulnerable areas of your body are covered with several layers of squamous tissue in order to protect the deeper tissues that are harder (more biologically expensive) to replace.
Squamous cells are somewhat disposable, meaning they take less time and less biological energy to be replaced. Squamous cells are small, so they can undergo mitotic cell division on short notice. For this reason, squamous epithelium is found in areas that need to be replaced rather frequently like the vagina, the esophagus and the mouth. Stratified squamous epithelium acts to protect against abrasion.
Squamous cells are somewhat disposable, meaning they take less time and less biological energy to be replaced. Squamous cells are small, so they can undergo mitotic cell division on short notice. For this reason, squamous epithelium is found in areas that need to be replaced rather frequently like the vagina, the esophagus and the mouth. Stratified squamous epithelium acts to protect against abrasion.
Slides of Stratified Squamous Epithelium
(Esophagus)
(Esophagus)
Know THIS slide for the practical exam!
Stratified Cuboidal Epithelial Tissue
- WILL NOT BE ON PRACTICAL -
Stratified cuboidal epithelium is composed of two or more layers of cube-shaped cells.
Distribution and Function - This type of tissue can be observed in sweat glands, mammary glands, and salivary glands and serve to protect the area.
Distribution and Function - This type of tissue can be observed in sweat glands, mammary glands, and salivary glands and serve to protect the area.
We DO NOT have this type of slide for the practical.
Stratified Columnar Epithelial Tissue
Stratified Columnar Epithelial Tissue is rarest tissue type of tissue.
|
Know THIS Slide for the Practical!
|
Stratified columnar epithelial tissue consists of several layers. Cuboidal cells may also be present in this type of tissue. When cuboidal cells are present, they are located near the basal membrane. Cells that are further toward the apical side of the tissue will appear more columnar or elongated.
Stratified columnar epithelial tissue can be found in the male urethra and in large ducts of some glands. This tissue functions as protection and secretion. |
|
Pseudostratified (Ciliated ) Columnar Epithelium
Columnar epithelium can also form a layer in which the nuclei are at different levels within the cells. This type of layering is called "pseudostratified", because, despite the cells forming a single layer, the variable position of the nuclei can make the tissue layer appears as though it was composed of two or more layers. It is for this reason that the layer is called "pseudo" (meaning "fake") - stratified.
Pseudostratified columnar epithelium is found in the esophagus, the trachea and the lining of the lungs. The main function of of this tissue is to move mucus.
Pseudostratified columnar epithelium is found in the esophagus, the trachea and the lining of the lungs. The main function of of this tissue is to move mucus.
IF YOU SEE CILIA, IN OUR PRACTICAL, IT IS GOING TO BE THE
Pseudostratified (Ciliated ) Columnar Epithelium
- looks like 6 layers and cilia are at the top
Pseudostratified (Ciliated ) Columnar Epithelium
- looks like 6 layers and cilia are at the top
Slides of Pseudostratified Columnar Epithelium
Know THIS slide for the practical exam!
Transitional Epithelium
Transitional epithelium lives up to its name. Its name is due to the 'transition' or changes in shape of the cells that make up the tissue. In this type of tissue, the most superficial (apical) cells get stretched out and deformed. Transitional tissues exist in areas of the body that undergo extreme stretching, like the bladder. The more 'stretchy' the tissue, the more 'bent out of shape' the apical cells become.
When transitional epithelium is not in its stretched shape (for example when your bladder is empty), in an empty bladder) the cells of the surface layers are large and rounded. When a transitional epithelium is stretched (as it would be in a full bladder) the cells of the surface layers are pulled into a flatter shape.
On a slide, the apical cells appear large and rounded, kind of like flower petals (see below!)
When transitional epithelium is not in its stretched shape (for example when your bladder is empty), in an empty bladder) the cells of the surface layers are large and rounded. When a transitional epithelium is stretched (as it would be in a full bladder) the cells of the surface layers are pulled into a flatter shape.
On a slide, the apical cells appear large and rounded, kind of like flower petals (see below!)
Slides of Transitional Epithelium
Know THIS Slide for the Practical!
Idealized slide of transitional epithelium.
|
More typical-looking slide of transitional epithelium you will see in a practical!
|
This type of tissue is in the bladder because it is very stretchy!
Summary of Epithelial Tissue
Table Courtesy of 4.2 Epithelial Tissue by Rice University
Table is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted. This textbook is available for free at open.bccampus.ca
opentextbc.ca/anatomyandphysiology/chapter/4-2-epithelial-tissue/
Table is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted. This textbook is available for free at open.bccampus.ca
opentextbc.ca/anatomyandphysiology/chapter/4-2-epithelial-tissue/
Your layers of epithelial tissue usually have some selective permeability that allows for absorption, filtration or excretion of certain substances. For example, the tissue epithelial tissue that lines your small intestines allows for the movement of nutrients from the small intestines to the body and the epithelial tissue of the kidney functions to filter out waste products.
Glandular Epithelial Tissue
.What is a GLAND? A gland is an organ that secretes particular chemical substances in or on the body, These substances act to serve a specific function for the body. There are two different kinds of glands at work in the human body; the endocrine glands and the exocrine glands. Your endocrine glands secrete hormones directly into your bloodstream or to nearby cells, Exocrine glands, on the other hand, secrete substances into tubes or ducts that lead to the outer or inner surfaces of your body (the can refer to either the outside of the body, or the inside of your "tube", as opposed to directly into the blood).
