Animal tissues consists of connective tissues, muscle tissues, nervous tissues and epithelial tissues. The tissues that line most of the cavities and organs are epithelial cells. These tissues consist of tightly clustered cells that are connected by desmosomes and tight junctions. There are many functions of epithelial cells.
Classification of the Epithelial Tissues
Epithelial tissues are classified according to their cellular morphology and the number of layers in the cell. When the tissue is just one cell thick, it is called simple epithelium and when it is two or more cells thick, is it called a stratified epithelium. Let us have a look at each of these cells in detail.
Simple Epithelial Cells
These are one cell thick and each cell comes in direct contact with the basement membrane. The simple epithelial cells are further classified according to the shape of the cells. These include the simple squamous, simple cuboidal, simple columnar and pseudostratified cells.
Stratified Epithelial Cells
Stratified epithelial cells are multi-layered cells and are found where the body needs to withstand mechanical or chemical trauma. These cells are flat and divided as stratified squamous cells, stratified cuboidal cells and stratified columnar cells.
What are the Functions of Epithelial Cells?
Functions of the epithelial cells consist of secretion, selective absorption, transcellular transportation, detection of sensation and protection. Let us have a look at the functions of each type of epithelial cells in the following table.
|Functions of Simple Epithelial Cells|
|Simple Squamous Epithelium||These cells form the lining of blood vessels. These cells are very thin and lie close together in tissues. They are usually found in areas where simple passive diffusion takes place. Examples of squamous epithelial cells include endothelium, pericardium, alveolar epithelium, and kidney capillaries.||These cells are very thin and therefore, do not offer any protection to any organs. Their function is to allow the movement of materials and nutrients through the cells, that is, passive diffusion.|
|Simple Columnar Epithelium||These are elongated column shaped cells that are found at the base of cells. They line the stomach and intestines, as well as present in the nose, ears and on the tongue. There are goblet cells located between the columnar epithelial cells in the duodenum.||The function of the columnar epithelial cells is secretion and absorption of nutrients. The columnar epithelial cells in the intestine contain microvilli that helps in increasing the surface are for absorption.|
|Simple Cuboidal Epithelium||These cells are cuboid in shape and have a spherical nucleus. These cells are present in the exocrine gland of the pancreas and the lining of kidney tubules.||As they are located in the pancreas and kidney tubules, they help in absorption of nutrients as well as secretion of hormones, sweat, wax, digestive enzymes and even milk.|
|Pseudostratified Epithelium Cells||These are simple epithelial cells that have different heights. This gives them an appearance of stratified epithelium in a cross-section. These cells contain small hair like membrane called cilia. Thus, they are also known as ciliated epithelial cells. They are present in the nose, bronchi, uterus, Fallopian tubes.||Pseudostratified cells help in trapping of pathogens, foreign particles, as well help in propelling the ovum from the ovaries into the uterus.|
|Functions of Stratified Epithelial Cells|
|Stratified Squamous Epithelium||The stratified squamous epithelium consists of flattened cell layers. They are present on the surface of the skin, lining of mouth, esophagus, anus and vagina.||These cells help in protecting the underlying tissues. The outer areas of the tissue undergo keratinization that helps in making the skin waterproof. However, in areas where the cells remain moist like the inner surface of mouth, etc. the cells do not undergo keratinization.|
|Stratified Cuboidal Epithelium||These form the sweat gland and are very rare in the human body. They are generally present in the lumen of mammary glands, sweat glands, salivary glands, pancreas, etc.||These cells offer protection to the underlying tissues.|
As you can see, these tissues help in protecting the body from desiccation, physical trauma, toxins, as well as radiation. They also help in regulation and exchange of chemicals of the underlying tissues and body cavity. Some epithelial cells are involved with the secretions of the hormones and some help in secretion of mucus, sweat, enzymes, etc. Hope the above information has helped you learn a few important points about the epithelial cells in the human body.