Principles of Anatomy and Physiology 14e with Atlas of the Skeleton Set (14th Edition)

Published by Wiley
ISBN 10: 1-11877-456-6
ISBN 13: 978-1-11877-456-4

Chapter 4 - The Tissue Level of Organization - Checkpoint: 11


The following is a list of the some of the ways in which epithelia and connective tissues are different: 1. An epithelium tissue consists of a large number of cells with very little extracellular matrix. Connective tissues also have cells. However, they are composed predominantly of extracellular matrix of fibers and ground substances 2. Adjacent epithelial cells are usually tightly bound by cell junctions of various kinds.These cell junctions are not found in connective tissues 3. Epithelia cover surfaces and line cavities and tubes.These tissues are therefore usually positioned above other tissues. Connective tissues do not usually occupy surface locations , instead they are generally found under epithelia and within other tissues such as muscles. 4. Epithelia are avascular tissues. Most types of connective tissues have rich vascular networks. 5. Epithelial tissue cells maintain a polarity between apical and basolateral surfaces of their plasma membranes. In stratified epithelia, the apical layer of cells has different capacities and functions from the middle and basal strata. This type of polarity is not found in most connective tissues. 6. Mature epithelia have greater regenerative capacities than mature connective tissues. In fact, the capacities of mature cartilage, and dense regular connective tissue to regenerate are distinctly poor. Nevertheless, one cannot say the same for blood or bone. 7. Epithelia protect underlying tissue from physical, radiant, and chemical damage. They also serve as filters and absorptive surfaces. Moreover, epithelial cells and organs secrete hormones and enzymes . They also rid the body of wastes. There are no connective tissue glands.

Work Step by Step

Epithelium and connective are two of the four major types of human tissues. Structurally, and functionally they differ in several ways. Some of these are composition of tissue; prevalence of cell junctions; anatomic position of tissue; vascularity; regenerative capacity ; chief functions. 1. Both epithelia and connective tissues have cells and extracellular components. An epithelium usually consists of a large number of closely packed cells with a minimum amount of noncellular substance or matrix. In contrast, connective tissues ( except blood) have very few cells and consist mainly of matrix ( ground substance plus fibers). 2. Cell junctions. The integrity of an epithelial sheet is maintained by the a variety of cell-linking devices which bind adjacent cells. Examples of these devices are tight junctions, adherens junctions, desmosomes, and gap junctions. These structures are absent in connective tissues in which cells are usually widely separated by large amounts of matrix. 3 . Epithelia cover surfaces and line cavities. This tissue always faces the external environment or a cavity. It is never found below any other kind of tissue. On the other hand, connective tissues are found below the basement membranes of epithelia. They are also located in various positions inside other types of tissues, such as muscle and nervous tissue. 4. Vascularity . Epithelia are usually avascular. Connective tissues --with the exception of tendons, ligaments and cartilage-- have rich blood supplies. In their usual position below epithelial basement membranes, loose connective tissues are ideally positioned to supply nutrients and oxygen to overlying epithelial layers. 5. Polarity. The apical layers of stratified epithelial have different capacities from their basal layers. Also, the apical surfaces of simple epithelia have different features and functions from their basolateral surfaces. Polarity is prominent in nervous tissue, also, but not in connective tissues. 6. Regenerative capacity. Both epithelia and connective tissues have protective functions. Consequently, their cells are often damaged and destroyed. Epithelia repair more readily and completely because of the regenerative capacity of basal cells. Connective tissue can also regenerate through the medium of stem cells; however, structures like tendons and ligaments repair very slowly and incompletely. 7,General functions. Epithelia function as coverings and linings of tissues and organs. They protect underlying tissues from physical and chemical damage.In addition, they are the surfaces through which selective absorption and filtering take place. Various kinds of glandular secretory functions are carried out by epithelia. Although connective tissues form the stroma of some glands, there are no connective tissue glands.
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