What Are The Characteristics Of Epithelial Tissue – Most epithelial tissues are essentially large cell membranes that are exposed to all the external surfaces of the body and line the external organs. Epithelium also forms much of the glandular tissue of the body. The skin is not the only area of the body exposed to the outside. Other areas include the airways, the digestive tract, as well as the urinary and reproductive systems, all of which are lined by epithelium. Hollow organs and body cavities that do not connect to the outside of the body, in which there are blood vessels and serous membranes, from endothelium (plural = endothelium), which is a type of epithelium.
Epithelial cells arise from all three major embryonic layers. Epithelia line the skin, parts of the mouth and nose, and develop the anus from the ectoderm. The cells lining the airways and most of the digestive system originate in the endoderm. The epithelium that lines the vessels in the lymphatic and cardiovascular system is derived from the mesoderm and is called the endothelium.
- 1 What Are The Characteristics Of Epithelial Tissue
What Are The Characteristics Of Epithelial Tissue
All epithelia share some important structural and functional characteristics. This tissue is highly cellular, with little or no extracellular material present between the cells. Adjacent cells form a special intercellular connection between cell membranes called cell junctions. Epithelial cells exhibit verticality with structural and functional differences between the exposed or apical cell surface and the basal surface of the nearest underlying body structure. The basal lamina, a mixture of glycoproteins and collagen, provides a site for attachment of the epithelium, separating it from the underlying tissue. The basal lamina adheres to the reticular lamina, which is separated from the underlying connective tissue, forming the basement membrane that supports it as a whole.
Types Of Tissues
Epithelial tissues are usually completely avascular. For example: no blood vessels cross the cell membrane to enter the tissue, and nutrients can reach the tissues or surfaces by diffusion or absorption. Many epithelial tissues can be rapidly damaged and replace dead cells. The clearing of damaged or dead cells is characteristic of the surface epithelium and allows our airways and digestive systems to rapidly replace damaged cells with new cells.
Epithelial tissues provide the body’s first line of protection from physical, chemical, and biological wear and tear. Epithelial cells act as gatekeepers regulating the permeability of the body and allowing selective transport of material across the body barrier. All substances that enter the body must pass through the epithelium. Some epithelia often include characteristic structures that allow selective transport of molecules and ions across their cell membranes.
Many epithelial cells are capable of secretion and mucous and release specific chemical compounds on their apical surfaces. The epithelium of the small intestine releases digestive enzymes, for example. The cells of the respiratory tract secrete mucous membranes that trap incoming microorganisms and particles. The glandular epithelium contains many secretory cells.
Epithelial cells are typically characterized by the distribution of organelles and networks of membrane bonds between their basal and apical surfaces. Particular structures found in some epithelial cells are adaptations for specific functions. Some organelles are secreted to the basal sides, while other organelles and extensions, such as cilia, are present on the apical surface.
Introduction To Sports Science. Epithelial Tissue Epithelial Tissue: Or Epithelium Is The Lining, Covering, And Glandular Tissue Of The Body. Glandular.
Cilia are microscopic extensions of the apical cell membrane that are supported by microtubules. They strike and move the fluids and particles in concert. Ciliated epithelium lines the ventricles of the brain where cerebrospinal fluid helps circulate. The ciliated epithelium of your airways forms a mucociliary escalator that sweeps dust particles and pathogens trapped in mucous secretions toward the throat. It is called an escalator because it constantly pushes upward with particles in the mucous membrane of wounds. On the other hand, nasal cilia sweep the mucous membrane towards your throat. In both cases, the transported materials are usually swallowed, and end up in the acidic environment of your stomach.
Epithelial cells are closely connected and are not separated from the intracellular material. Three basic types of junctions allow different levels of interaction between cells: tight junctions, anchor junctions, and junctions (Figure 4.5).
Figure 4.5 Types of Cell Junctions The three basic types of cell junctions are tight junctions, break junctions, and anchor junctions.
At the extreme end of the spectrum is the tight junction that separates cells into apical and basal cells. When two adjacent epithelial cells form a tight junction, there is no extracellular space between them and the movement of substances through the extracellular space between the cells is blocked. This enables epithelia to act as selective barriers. Anchorages are various cell-to-cell junctions that help stabilize epithelial tissues. Anchor junctions are common on the lateral and basal surfaces of cells where they provide strong and flexible connections. There are three types of anchorages: desmosomes, hemidesmosomes, and adhesion. Desmosomes occur unevenly in cell membranes. They are composed of structural proteins on the inner surface of the cell membrane. The cadherin adhesion molecule is embedded in these envelopes and projects through the cell membrane with cadherin molecules of adjacent cells. These connections are very important in keeping the cells together. Hemidesmosomes, which look like half of desmosomes, connect cells to the extracellular matrix, for example, the basal lamina. While similar in appearance to desmosomes, they include adhesion proteins called integrins called cadherins. Adherent junctions use either cadherins or dangling integrins to connect to other cells or the matrix. Junctions are characterized by the presence of the contractile protein actin located on the surface of the cell’s cytoplasmic membrane. Actin can connect unevenly separated or form a belt structure within the cell. These combinations affect the shape and complexity of the epithelial tissue.
Pseudostratified Columnar Epithelium
In contrast to tight junctions and anchors, gap junctions enable intercellular passage between the membranes of adjacent cells to facilitate the movement of small molecules and ions between the cytoplasm of adjacent cells. These junctions allow the electrical and metabolic connection of neighboring cells, which function in large groups of cells.
Epithelial tissues are classified according to the shape of the cells and the number of cell layers formed (Figure 4.6). Cell shapes can be scaly (flat and thin), cuboidal (a box wider than tall), or columnar (rectangular, taller than wide). Equally, the number of cell layers in the tissue can be one, where every cell is placed on the basal lamina, which is a simple epithelium, or more than one, which is a stratified epithelium and rests only on the basal layer of basal cells. plate Pseudostratified (pseudo- = “false”) describes a tissue with a single layer of irregularly formed cells that give the appearance of more than one layer. Transitional describes a form of specialized stratified epithelium in which the shape of the cells can vary.
Figure 4.6 Epithelial tissue cells Simple epithelial tissue is organized as a single layer of cells and stratified epithelial cells are formed by several layers of cells.
The shape of the cells in a single layer of simple epithelial cells shows the operation of those cells. The cells of simple squamous epithelium have the appearance of scales. The nuclei of squamous cells tend to be flat, horizontal, and elliptical, expressing the shape of the cell. The endothelium is the epithelial tissue that lines the vessels of the lymphatic and cardiovascular systems, and consists of a single layer of squamous cells. A simple squamous epithelium is present because of the thinness of the cell where the rapid passage of chemical compounds is observed. The alveoli of the lungs where gases diffuse, the segments of the kidney tubules, and the capillary lining are also made of simple squamous epithelial tissue. Mesothelium is a simple squamous epithelium that forms the surface of the serous membrane layer forming the body cavities and internal organs. Its primary function is to provide a smooth and protective surface. Mesothelial cells are epithelial scales that secrete the mesothelium lubricating fluid.
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In simple cuboidal epithelium, the nucleus of the cells appears as round cells and is located approximately around the center of the cell. These epithelia are active in the secretion and effusion of molecules. Simple cuboidal epithelia are observed in the lining of the renal tubules and in the ducts of the glands.
In simple columnar epithelium, the nucleus of a tall columnar cell tends to elongate and is located at the basal end of the cells. Like the cuboidal epithelia, this epithelium acts in the absorption and secretion of molecules. Simple columnar epithelium forms the lining of certain sections of the digestive system and parts of the female reproductive tract. Ciliated columnar epithelium consists of simple columnar epithelial cells with cilia on the apical surface. These epithelial cells are found in the lining of the tubes and parts of the respiratory system, where the beating of the cilia helps to remove particulate matter.
Pseudostratified columnar epithelium is a type of epithelium that appears to be stratified, but consists of a single layer of irregularly shaped and differently sized columnar cells. In pseudostratified
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