Pseudostratified (pseudo- = “false”) describes tissue with a single layer of irregularly shaped cells that give the appearance of more than one layer. This epithelium protects against physical and chemical wear and tear. Squamous cell nuclei tend to be flat, horizontal, and elliptical, mirroring the form of the cell. The cells in simple squamous epithelium have the appearance of thin scales. Where in the body would one find non-keratinizing stratified squamous epithelium? In pseudostratified epithelium, nuclei of neighboring cells appear at different levels rather than clustered in the basal end. Ciliated columnar epithelium is composed of simple columnar epithelial cells with cilia on their apical surfaces. All substances that enter the body must cross an epithelium.

Certain organelles are segregated to the basal sides, whereas other organelles and extensions, such as cilia, when present, are on the apical surface. For example, a goblet cell is a mucous-secreting unicellular “gland” interspersed between the columnar epithelial cells of mucous membranes (Figure 4.4). Hormones are released into the interstitial fluid, diffused into the bloodstream, and delivered to targets, in other words, cells that have receptors to bind the hormones. Mammalian skin is an example of this dry, keratinized, stratified squamous epithelium. In both cases, the transported materials are usually swallowed, and end up in the acidic environment of your stomach. They beat in unison and move fluids as well as trapped particles. Epithelial tissues are nearly completely avascular. to explore the tissue sample in greater detail. Ciliated epithelium lines the ventricles of the brain where it helps circulate the cerebrospinal fluid. The mesothelium is a simple squamous epithelium that forms the surface layer of the serous membrane that lines body cavities and internal organs. The other surface is attached to tissue by a membrane, which consists of fibres and polysaccharides secreted by epithelial cells. The epithelium of the small intestine releases digestive enzymes, for example. Transitional describes a form of specialized stratified epithelium in which the shape of the cells can vary. Simple squamous epithelium, because of the thinness of the cell, is present where rapid passage of chemical compounds is observed. There is an exposed edge of epithelial tissue known as the apical surface and an anchoring layer called the basal surface that attaches the epithelial tissue to the underlying connective tissue. A gland can be classified as an endocrine gland, a ductless gland that releases secretions directly into surrounding tissues and fluids (endo- = “inside”), or an exocrine gland whose secretions leave through a duct that opens directly, or indirectly, to the external environment (exo- = “outside”). It is found only in the urinary system, specifically the ureters and urinary bladder. Epithelial tissues provide the body’s first line of protection from physical, chemical, and biological wear and tear. Simple cuboidal epithelia are observed in the lining of the kidney tubules and in the ducts of glands. In simple columnar epithelium, the nucleus of the tall column-like cells tends to be elongated and located in the basal end of the cells. For instance, no blood vessels cross the basement membrane to enter the tissue, and nutrients must come by diffusion or absorption from underlying tissues or the surface. When the bladder is empty, this epithelium is convoluted and has cuboidal apical cells with convex, umbrella shaped, apical surfaces. Mesothelial cells are squamous epithelial cells that secrete a fluid that lubricates the mesothelium. Watch this video to find out more about the anatomy of epithelial tissues. Sloughing off of damaged or dead cells is a characteristic of surface epithelium and allows our airways and digestive tracts to rapidly replace damaged cells with new cells. Similarly, the number of cell layers in the tissue can be one—where every cell rests on the basal lamina—which is a simple epithelium, or more than one, which is a stratified epithelium and only the basal layer of cells rests on the basal lamina. Epithelial tissues are classified according to the shape of the cells and number of the cell layers formed (Figure 4.3).

Most glands consist of groups of epithelial cells. The shape of the cells in the single cell layer of simple epithelium reflects the functioning of those cells.

Many epithelial cells are capable of secretion and release mucous and specific chemical compounds onto their apical surfaces. The top layer may be covered with dead cells filled with keratin. Epithelial layers are avascular, but innervated. Stratified cuboidal epithelium and stratified columnar epithelium can also be found in certain glands and ducts, but are uncommon in the human body. Epithelial tissue is composed of cells laid together in sheets with the cells tightly connected to one another.

Most epithelial tissues are essentially large sheets of cells covering all the surfaces of the body exposed to the outside world and lining the inside and covering the outside of organs.

A few examples of endocrine glands include the anterior pituitary, thymus, adrenal cortex, and gonads. Its primary function is to provide a smooth and protective surface. Generalized Functions of Epithelial Tissue, Glandular Epithelium – endocrine and exocrine, http://openstaxcollege.org/files/textbook_version/low_res_pdf/13/col11496-lr.pdf, Explain the structure and function of epithelial tissue, Distinguish between simple epithelia and stratified epithelia, as well as between squamous, cuboidal, and columnar epithelia, Describe the structure and function of endocrine and exocrine glands and their respective secretions. They are all discharged through tubular ducts.



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