What Is The Role Of Epithelial Tissue – Most epithelial tissues are essentially large sheets of cells that cover all body surfaces exposed to the outside world and line the exterior of organs. Epithelium also makes up much of the body’s glandular tissue. The skin is not the only part of the body exposed to the outside. Other areas include the respiratory tract, digestive tract, and urinary and reproductive systems, all of which are lined by epithelium. Hollow organs and body cavities that are not connected to the outside of the body, including blood vessels and serous membranes, are lined by endothelium (plural = endothelium), a type of epithelium.
Epithelial cells arise from all three major layers of the embryo. Epithelium forms from the ectoderm, which covers the skin, parts of the mouth and nose, as well as the anus. The cells that line the respiratory tract and most of the digestive system originate in the endoderm. The epithelium that lines the blood vessels of the lymphatic and cardiovascular systems originates from the mesoderm and is called the endothelium.
What Is The Role Of Epithelial Tissue
All epithelia share some important structural and functional features. This tissue is highly cellular, with little or no extracellular material between the cells. Adjacent cells form a specialized intercellular connection between their cell membranes called a cell junction. Epithelial cells have polarity, with differences in structure and function between the exposed or apical surface of the cell and the basal surface, which is close to the underlying body structures. The basal lamina, a mixture of glycoproteins and collagen, provides a site of attachment for the epithelium, separating it from the underlying connective tissue. The basal layer joins the reticular layer, which is secreted by the underlying connective tissue, to form the basement membrane, which helps hold it all together.
Tissue And Its Classification
Epithelial tissue is almost completely avascular. For example, no blood vessels cross the basement membrane to enter the tissue, and nutrients must come by diffusion or absorption from the underlying tissue or surface. Many epithelial tissues are able to quickly replace damaged and dead cells. Shedding damaged or dead cells is a property of the surface epithelium and allows our respiratory and digestive tracts to quickly replace damaged cells with new cells.
Epithelial tissue provides the body’s first line of defense against physical, chemical and biological wear and tear. Epithelial cells act as the body’s gatekeepers, controlling permeability and allowing the selective transfer of materials across a physical barrier. All substances entering the body must cross the epithelium. Some epithelia often contain structural features that allow selective transport of molecules and ions across their cell membranes.
Many epithelial cells are capable of shedding and secreting mucus and specific chemical compounds on their apical surfaces. The epithelium of the small intestine releases, for example, digestive enzymes. The cells that line the airways secrete mucus that traps incoming microorganisms and particles. The epithelium of the gland contains many secretory cells.
Epithelial cells are typically characterized by a polarized distribution of organelles and membrane-bound proteins between their basal and apical surfaces. Special structures found in some epithelial cells are adaptations for certain functions. Some organelles are separated on the basal sides, while other organelles and extensions such as cilia, if any, are on the apical surface.
Describe Various Types Of Epithelial Tissues With The Help Of Labeled Diagrams
Cilia are microscopic extensions of the apical cell membrane supported by microtubules. They beat in unison and move fluids as well as trapped particles. Cilied epithelium lines the ventricles of the brain, where it helps circulate the cerebrospinal fluid. The ciliated epithelium of your airways forms a mucociliary escalator that sweeps dust and pathogen particles trapped in secreted mucus toward the throat. It is called an escalator because it continuously pushes up mucous membranes with trapped particles. In contrast, the nasal cilia sweep the mucous blanket down toward your throat. In both cases, the transported materials are usually swallowed and end up in the acidic environment of your stomach.
Epithelial cells are tightly packed and not separated by intracellular material. Three basic types of junctions provide varying degrees of interaction between cells: tight junctions, anchoring junctions, and gap junctions (Figure 4.5).
4.5. image. Types of cell junctions The three main types of cell junctions are tight junctions, gap junctions, and anchoring junctions.
At one end of the spectrum is the tight junction that separates cells into apical and basal compartments. 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 allows the epithelium to act as a selective barrier. The anchoring junction includes several types of cell junctions that help stabilize epithelial tissue. Anchor junctions are distributed on the lateral and basal surfaces of cells, where they provide strong and flexible connections. There are three types of anchoring junctions: desmosomes, hemidesmosomes, and adherens. Desmosomes occur in patches on cell membranes. Patches are structural proteins on the inner surface of the cell membrane. An adhesion molecule, cadherin, is embedded in these patches and protrudes through the cell membrane to connect with cadherin molecules of neighboring cells. These connections are especially important for holding cells together. Hemidesmosomes, which look like half a desmosomes, connect cells to the extracellular matrix, such as the basal lamina. Although similar in appearance to desmosomes, they contain adhesion proteins called integrins rather than cadherins. Adherens junctions use either cadherins or integrins, depending on whether they are associated with other cells or the matrix. Junctions are characterized by the presence of the contractile protein actin, which is located on the cytoplasmic surface of the cell membrane. Actin can connect isolated patches or form a belt-like structure inside the cell. These compounds affect the shape and fold of the epithelial tissue.
Tissues & Integument System Crossword
Unlike tight and anchored junctions, a gap junction forms an 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 provide electrical and metabolic coupling between neighboring cells, coordinating activity in large groups of cells.
Epithelial tissue is classified by cell shape and the number of cell layers formed (Figure 4.6). Cell shapes can be planar (flattened and thin), cuboidal (box-like, as wide as it is tall), or columnar (rectangular, longer than it is wide). Similarly, the number of cell layers in a tissue can be one, where each cell rests on a basal layer, which is a simple epithelium, or more than one, which is a stratified epithelium, with only the basal layer of cells resting on the basal layer. lamina. Pseudostratified (pseudo- = “false”) describes tissue with a single layer of irregularly shaped cells, giving the appearance of more than one layer. The transition period describes the form of a specialized stratified epithelium in which the cell shape can vary.
4.6. figure Epithelial Tissue Cells Simple epithelial tissue is arranged as a single layer of cells, and stratified epithelial tissue consists of several layers of cells.
The shape of the cells in a single cell layer of a simple epithelium reflects the function of these cells. The cells of the simple squamous epithelium have thin scales. The nuclei of squamous cells tend to be flat, horizontal and elliptical, reflecting the shape of the cell. The endothelium is the epithelial tissue that lines the blood vessels of the lymphatic and cardiovascular systems and is composed of a single layer of squamous cells. Simple squamous epithelium, due to the thinness of the cell, is located in places where a rapid transition of chemical compounds is observed. The alveoli of the lungs, where gases diffuse, the renal tubule segments, and the capillary lining are also made of simple squamous epithelial tissue. The mesothelium is a simple squamous epithelium that forms the surface layer of the serous membrane that lines the body cavities and internal organs. Its main function is to provide a smooth and protective surface. Mesothelial cells are squamous epithelial cells that secrete a fluid that lubricates the mesothelium.
File:423 Table 04 02 Summary Of Epithelial Tissue Cellsn Hu.jpg
In simple cuboidal epithelium, the nucleus of the box-shaped cells appears round and is usually located near the center of the cell. These epithelia are active in the secretion and absorption of molecules. A simple cuboidal epithelium is observed in the lining of the renal tubules and glandular ducts.
In simple columnar epithelium, the nucleus of the tall columnar cells tends to be elongated and located at the basal end of the cells. Like the cuboidal epithelium, this epithelium is also active in the absorption and secretion of molecules. Simple columnar epithelium lines some parts of the digestive system and parts of the female reproductive tract. Ciliary columnar epithelium consists of simple columnar epithelial cells with cilia on their apical surfaces. These epithelial cells are found in the lining of the fallopian tubes and parts of the respiratory system, where cilia help remove particles.
Pseudostratified columnar epithelium is a type of epithelium that appears to be stratified but is instead composed of a single layer of irregularly shaped and varying-sized columnar cells. In a pseudostratified manner
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