Epithelial tissue is generated by a continuous layer of cells that are closely packed together. It is only one surface of the epithelial tissue that is exposed to the outside environment or to bodily fluid. Epithelial cells secrete polysaccharides and fibers that are attached to the other surface of the membrane, which is attached to the tissue via a membrane.
The Different Types of Epithelial Tissue
Epithelial cells are classified into three categories, each of which has a distinct structure and function.
- Squamous Epithelium – These cells are thin and flat, and they are found in the skin.
- Cuboidal Epithelium — These cells are short cylindrical cells that appear hexagonal in cross-section when viewed from above or below.
- Columnar Epithelium – These are cylindrical cells that are long or column-like in shape, with the nucleus located at the base.
Epithelial tissue is classified into two types: simple epithelium and stratified or compound epithelium. Simple epithelium has only one layer, whereas stratified or compound epithelium has multiple layers.
1.Simple epithelium is made up of a single layer of cells and is primarily responsible for secretion or absorption of substances.
2.Compound (Stratified) Epithelium- This type of epithelium is composed of two or more layers of cells and primarily serves a protective function.
3.It is composed of cuboidal or columnar cells, which make up the glandular epithelium. They are very specialized in the secretion of substances.
Goblet cells, for example, are unicellular glandular cells that have been isolated.
4.Multicellular- a group of cells, such as salivary glands- that function together.
Cilia can be found on the columnar or cuboidal epithelium, and this type of epithelium is referred to as ciliated epithelium. Fallopian tubes and bronchioles are examples of mucus-moving structures that aid in the movement of mucus in a certain direction.
Structure of Epithelial Tissue
There is only a small amount of intercellular substance between the cells. In the epithelium, there are specialised junctions that connect individual cells and allow them to communicate with one another.
1.Tight junctions– they help to avoid leaking between tissues.
2.Adhering connections– These junctions help to maintain the tissues next to each other properly glued together.
3.Gap junctions– These junctions allow ions and molecules to pass more freely across the tissue.
4.Membranes are formed by epithelial cells. The epithelial membrane is composed of a layer of epithelial tissue that is supported by connective tissue at the base. Mucous membranes and serous membranes are the two types of epithelial membranes found in the body.
5.The mucous membrane is sometimes referred to as the mucosa. In the presence of goblet cells, which release mucus, there is mucus production. The mucus aids in the lubrication, protection, and smooth movement of materials because to its properties. It helps to keep tissues from drying out. It is found in the lining of body cavities such as the respiratory and digestive tracts, which are accessible from the outside of the body.
6.Serous membrane: The serous membrane is found in the lining of body cavities that do not open to the outside world, such as the lining of the pleural cavity and the pericardium. These membranes, which are composed of simple squamous epithelium, secrete the fluid that is contained within the cavity.
7.Epithelial cells are responsible for the formation of glands. Exocrine glands and endocrine glands are the two types of glands that exist. Goblet cells and sweat glands are examples of exocrine glands that discharge their product into a duct. Endocrine glands are referred to as ductless glands because they release their product directly into the bloodstream or intestinal fluid, such as hormones, rather than through a duct.
The Functions of Epithelial Tissue
1.Protection: Because it covers the entire body surface, it serves as the first line of defense against any type of mechanical injury, chemical exposure, excessive fluid loss, and infections, among other threats. When dust particles are trapped by iliary projections in the nose or upper respiratory system, they are prevented from entering the body and causing illness.
The epithelium lining of the digestive tract is responsible for the absorption of water and nutrients.
2.Interchange of substances: Epithelial tissue is responsible for regulating the exchange of substances between the body and the external environment, as well as the exchange of substances within the body between different organs. Everything that enters the body or enters the bloodstream through absorption must first pass through the epithelial barrier before entering the body.
3.Sensation: Sensory receptors are found in the epithelial tissue of the nose, eyes, and ears, as well as in the taste buds, and they aid in the transmission of information from external stimuli to the central nervous system.
4.Secretion: Hormones, enzymes, saliva, mucus, perspiration, and other bodily fluids are secreted by various glands composed of epithelial cells.
Conclusion
The most significant distinction between epithelial and connective tissue is found in the cells that make up each type of tissue, as well as their roles. Squamous, cuboidal, and columnar epithelial tissue are the three types of cells that make up epithelial tissue. Cells in connective tissue, as well as cartilaginous, collagenous, elastic, and fatty tissues, are immersed in an indeterminate matrix that surrounds them. Fibroblasts are the most frequent type of cell, although there are also macrophages, mast cells, adipocytes, plasma cells, leukocytes, and other types. Body cavities, blood arteries, the digestive system, and other sensitive internal organs are lined with epithelial tissue, which aids in excretion, transportation, absorption, protection, and secretion by performing a variety of functions. Connective tissue, on the other hand, is responsible for the formation of connections, the support of other tissues, and the binding of other tissues.