Additionally, there are pseudostratified epithelia and transitional epithelia. Examples of Epithelia Simple Epithelium Simple epithelia are made of a single layer of cells that are in direct contact with the basement membrane with a common apical surface. These cells can be squamous, cuboidal, or columnar. Simple squamous epithelium is found in the alveoli of lungs, and its structure is important for the exchange of gases between the blood and lungs.
In general, epithelial tissues are classified by the number of their layers and by the shape and function of the cells. Squamous epithelium has cells that are wider than their height flat and scale-like.
Cuboidal epithelium has cells whose height and width are approximately the same cube shaped. Columnar epithelium has cells taller than they are wide column-shaped.
By layer, epithelium is classed as either simple epithelium, only one cell thick unilayered or stratified epithelium as stratified squamous epitheliumstratified cuboidal epitheliumand stratified columnar epithelium that are two or more cells thick multi-layered  and both types of layering can be made up of any of the cell shapes.
This kind of epithelium is therefore described as pseudostratified columnar epithelium. In general, it is found where absorption and filtration occur. The thinness of the epithelial barrier facilitates these processes. The four major classes of simple epithelium are: Non-ciliated epithelium can also possess microvilli.
Some tissues contain goblet cells and are referred to as simple glandular columnar epithelium. The ciliated type is also called respiratory epithelium as it is almost exclusively confined to the larger respiratory airways of the nasal cavity, trachea and bronchi. Stratified epithelium[ edit ] Stratified epithelium differs from simple epithelium in that it is multilayered.
It is therefore found where body linings have to withstand mechanical or chemical insult such that layers can be abraded and lost without exposing subepithelial layers. Cells flatten as the layers become more apical, though in their most basal layers the cells can be squamous, cuboidal or columnar.
This specialization makes the epithelium waterproof, so is found in the mammalian skin. The lining of the esophagus is an example of a non-keratinized or "moist" stratified epithelium.
These nuclei are pyknoticmeaning that they are highly condensed. Parakeratinized epithelium is sometimes found in the oral mucosa and in the upper regions of the esophagus.
It is sometimes called urothelium since it is almost exclusively found in the bladder, ureters and urethra. Type Squamous Squamous cells have the appearance of thin, flat plates that can look polygonal when viewed from above.
The cells fit closely together in tissues; providing a smooth, low-friction surface over which fluids can move easily.
The shape of the nucleus usually corresponds to the cell form and helps to identify the type of epithelium. Squamous cells tend to have horizontally flattened, nearly oval shaped nuclei because of the thin flattened form of the cell.
Squamous epithelium is found lining surfaces such as the skinand alveoli in the lungenabling simple passive diffusion as also found in the alveolar epithelium in the lungs. Specialized squamous epithelium also forms the lining of cavities such as in blood vessels, as endothelium and in the pericardiumas mesothelium and in other body cavities.
Cuboidal Cuboidal epithelial cells have a cube-like shape and appear square in cross-section. The cell nucleus is large, spherical and is in the center of the cell.
Cuboidal epithelium is commonly found in secretive tissue such as the exocrine glandsor in absorptive tissue such as the pancreas, the lining of the kidney tubules as well as in the ducts of the glands.
The germinal epithelium that covers the female ovaryand the germinal epithelium that lines the walls of the seminferous tubules in the testes are also of the cuboidal type.
Cuboidal cells provide protection and may be active in pumping material in or out of the lumen, or passive depending on their location and specialisation.
Simple cuboidal epithelium commonly differentiates to form the secretory and duct portions of glands. Columnar Columnar epithelial cells are elongated and column-shaped and have a height of at least four times their width. Their nuclei are elongated and are usually located near the base of the cells.
Columnar epithelium forms the lining of the stomach and intestines. The cells here may possess microvilli for maximising the surface area for absorption and these microvilli may form a brush border. Other cells may be ciliated to move mucus in the function of mucociliary clearance.
Other ciliated cells are found in the fallopian tubesthe uterus and central canal of the spinal cord.
Some columnar cells are specialized for sensory reception such as in the nose, ears and the taste buds.Epithelial tissue is composed of cells laid together in sheets with the cells tightly connected to one another.
Epithelial layers are avascular, but innervated. Epithelial cells have two surfaces that differ in both structure and function. Epithelium (/ ˌ ɛ p ɪ ˈ θ iː l i ə m /) is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue.
Epithelial tissues line the outer surfaces of organs and blood vessels throughout the body, as well as the inner surfaces of cavities in many internal organs. The list is long. Roles of epithelial tissues could be: Keratinised skin epithelium protects body from invasion of germs.
Oral epithelial layer has antibodies to provide immunity. Inner lining of hollow organs, like gall bladder, made of epithelium. Ciliated epithelium of trachea helps in moving the mucus out, ciliated epithelium of fallopian tube helps in moving fertilised egg towards uterine.
Roles of epithelial tissues could be: Keratinised skin epithelium protects body from invasion of germs. Oral epithelial layer has antibodies to provide immunity.
Inner lining of hollow organs, like gall bladder, made of epithelium. Epithelial tissue, or epithelium, has the following general characteristics: These thick cells serve to protect underlying tissues or may function to absorb substances. Some have microvilli, minute surface extensions, to increase surface area for absorbing substances, while others may have cilia that help move substances over their surface.
Epithelial tissue is composed of cells laid together in sheets with the cells tightly connected to one another.
Epithelial layers are avascular, but innervated. Epithelial cells have two surfaces that differ in both structure and function.