Do not open to the outside and they cover the organs

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do not open to the outside, and they cover the organs located within those cavities. They are essentially membranous bags,with mesothelium lining the inside and connective tissue on the outside. Serous fluid secreted by the cells of the thinsquamous mesothelium lubricates the membrane and reduces abrasion and friction between organs. Serous membranes areidentified according locations. Three serous membranes line the thoracic cavity; the two pleura that cover the lungs and thepericardium that covers the heart. A fourth, the peritoneum, is the serous membrane in the abdominal cavity that coversabdominal organs and forms double sheets of mesenteries that suspend many of the digestive organs.The skin is an epithelial membrane also called thecutaneous membrane. It is a stratified squamous epithelialmembrane resting on top of connective tissue. The apical surface of this membrane is exposed to the external environmentand is covered with dead, keratinized cells that help protect the body from desiccation and pathogens.4.2|Epithelial TissueBy the end of this section, you will be able to:Explain the structure and function of epithelial tissueDistinguish between tight junctions, anchoring junctions, and gap junctionsDistinguish between simple epithelia and stratified epithelia, as well as between squamous, cuboidal, and columnarepitheliaDescribe the structure and function of endocrine and exocrine glands and their respective secretionsMost epithelial tissues are essentially large sheets of cells covering all the surfaces of the body exposed to the outside worldand lining the outside of organs. Epithelium also forms much of the glandular tissue of the body. Skin is not the only area ofthe body exposed to the outside. Other areas include the airways, the digestive tract, as well as the urinary and reproductivesystems, all of which are lined by an epithelium. Hollow organs and body cavities that do not connect to the exterior of thebody, which includes, blood vessels and serous membranes, are lined by endothelium (plural = endothelia), which is a typeof epithelium.Epithelial cells derive from all three major embryonic layers. The epithelia lining the skin, parts of the mouth andnose, and the anus develop from the ectoderm. Cells lining the airways and most of the digestive system originate in theendoderm. The epithelium that lines vessels in the lymphatic and cardiovascular system derives from the mesoderm and iscalled an endothelium.All epithelia share some important structural and functional features. This tissue is highly cellular, with little or noextracellular material present between cells. Adjoining cells form a specialized intercellular connection between their cellmembranes called acell junction. The epithelial cells exhibit polarity with differences in structure and function between theexposed orapicalfacing surface of the cell and the basal surface close to the underlying body structures. Thebasal lamina,a mixture of glycoproteins and collagen, provides an attachment site for the epithelium, separating it from underlying

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Term
Fall
Professor
N/A
Tags
Physiology, Anatomy, Epithelial tissue

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