Squamous: Definition, Classification and Structure

A collection of tissues termed epithelial tissues, which are usually referred to as epithelium, lines all of the body's layers and organs. They cover the outside and inside surfaces of all internal and external organs. The permeability of epithelial tissue is quite high. As a result, it is important for the exchange of chemicals between cells and for maintaining osmoregulation. The epithelium is classified as simple epithelium or complex epithelium depending on the number of layers of cells it contains. Protection, secretion, absorption, and sensing are the primary activities of epithelial tissue.

Tissues are a collection of cells with similar structure, function, and origin. Tissue structure in animals is determined by its function. Four distinct types of tissues make up an animal's body. They've been divided into categories depending on cell type, function, and location in the body.

Classification of Epithelial Tissues

Epithelial Tissue is classified into two types based on layer:

Unilayered epithelial/simple epithelial: Having only one layer. They come into direct touch with the basement membranes that divide it from the connective tissue beneath. They are further subdivided into the following categories:

Simple Squamous Epithelium: Their cells have a scale-like appearance and are flattened or spherical in shape. Capillary walls, pericardial, pleural, and peritoneal cavity linings, and alveolar linings of the lungs are examples.

Simple Cuboidal Epithelium: These cells might be secretory, absorptive, or excretory in nature. Kidney collecting ducts, pancreas, and salivary gland are examples.

Simple Columnar Epithelium: These cells might be secretive, absorptive, or excretory. Simple glandular columnar epithelium refers to certain tissues that contain goblet cells. These are located in the stomach, colon, and rectum and produce mucus.

Pseudostratified Epithelium: Ciliated or nonciliated pseudostratified epithelium. 

Respiratory epithelium is an example of ciliated epithelium.

Stratified Epithelium: A multilayered epithelium with two or more cells. They are also divided into three categories:

1. Stratified Squamous Epithelium: These epithelial layers primarily protect the skin from abrasion and water loss. They're mostly found in the mouth, oesophagus, and larynx. Cuboidal epithelium stratified:
2. Stratified Columnar Epithelium: The major purpose of this type of epithelium is to secrete and protect the body. They can be found in the eye's conjunctiva coating.
3. Stratified Cuboidal Epithelium: The major purpose of this type of epithelium is to protect the body. They mostly line the sweat gland excretory ducts, which are huge ducts of excretory glands.

Structure of Epithelium

They're made up of layers of cells that are closely packed together. They are either exposed to the outside environment or to bodily fluids. Between the cells of the epithelium, there exist specialised junctions. The following are some of these intersections:

Tight Junctions: They primarily limit tissue leakage.

Adherens Junction: They aid in the correct cementation of neighbouring tissues.

Gap Junctions aid in the transport of ions and molecules across tissue.

Connective Tissues

They link and support the body's many tissues, organs, and components, as their name implies. Connective tissues are the most numerous among animal tissues in the body. Connective tissue cells are widely dispersed throughout the body and are freely organised in a matrix. Areolar tissue, adipose tissue (fat), blood, bone, and cartilage are examples of connective tissues. Except for blood cells, all other cells produce collagen (elastin), which gives tissues their elasticity and flexibility.

Functions of Epithelial Cells

Secretion Process: The majority of epithelial cells have the potential to secrete macromolecules. The glandular epithelium is one of the greatest examples. Because the endocrine gland is secretive in nature, it secretes hormones directly into the circulation, including insulin, tyroxin, and other hormones. Exocrine glands, which are similarly secretive, discharge hormones into ducts, such as sebum from the skin and digesting enzymes from the small intestine.

Absorption Process: The absorption process is mostly carried out by surface epithelia with the assistance of microvilli, which enhance the surface area available for absorption. The small intestine's columnar epithelium is another example.

Transportation: Different pumps are controlled by epithelial tissues. Example of a kidney's hydrogen ion pump (H+ ion pump) in action during urine production.

Process of Protection: They serve as both selective and protective barriers. Intoxication, ripping, and infections are among side effects. Epithelial cells may acquire receptor information, such as sensory information, and transform it into brain impulses. The olfactory nasal mucosa is an example of epithelial tissue that detects scents from outside and transmits this information to the central nervous system.

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Things to Remember

• Epithelial cells are a bunch of tissues present on the surface of different organs of the body.
• An animal body is formed of four distinct types of tissues.
• Adipose tissues store fat globules in the skin and organs.
• Epithelial cells perform absorption, secretion, transportation, and protection against infections.
• The epithelial cells are either exposed to the bodily fluids or to the outside environment.