Chapter 4 Study Guide
Individual body cells are specialized
-Each type performs specific functions that help maintain homeostasis
Tissues are groups of cells that are similar in structure and perform a common function
Histology – study of tissues
PRIMARY TISSUE TYPES:
Epithelial Tissue (or epithelium) is a sheet of cells that covers a body surface or lines a body cavity
Occurs in the body as covering and lining epithelium and glandular epithelium
Covering and lining epithelium forms the outer layer of the skin, and lines the open cavities of the cardiovascular, digestive, and respiratory systems, and covers the walls and organs of the ventral body cavity (internal and external surfaces)
Glandular epithelium fashions the glands of the body
Epithelial Tissue Functions:
Five Characteristics of Epithelial Tissues:
All epithelia have an apical surface, and upper free surface exposed to the body exterior or the cavity of an internal organ, and a lower attached basal surface. (Both surfaces differ in structure and function)
Apical surfaces are smooth and slick, and most have microvilli which are fingerlike extensions of the plasma membrane. Microvilli increase the exposed surface area.
Some epithelia, such as the lining of the trachea, have motile cilia (tiny hairlike projections) that propel substances along their free surface.
Lying adjacent to the basal surface of an epithelium is a thin supporting sheet called the basal lamina. This noncellular, adhesive sheet consists largely of glycoproteins secreted by the epithelial cells plus some fine collagen fibers. The basal lamina acts a selective filter that determines which molecules diffusing from the underlying connective tissue are allowed to enter the epithelium. The basal lamina also acts as a scaffolding along which epithelial cells can migrate to repair a wound. 2)
Epithelial cells fit close together to form continuous sheets. Adjacent cells are bound together at many points by lateral contacts, including tight junctions and desmosomes. 3)
SUPPORTED BY CONNECTIVE TISSUE
All epithelial sheets rest upon and are supported by connective tissue. Just deep to the basal lamina is the reticular lamina, a layer of extracellular material containing a fine network of collagen protein fibers that “belongs to” the underlying connective tissue. Together the two laminae form the basement membrane. The basement membrane reinforces the epithelial sheet, helping it to resist stretching and tearing forces, and defines the epithelial boundary. 4)
AVASCULAR BUT INNERVATED
Although epithelium is innervated (supplied by nerve fibers) it is avascular (contains no blood vessels). Epithelial cells are nourished by substances diffusing from blood vessels in the underlying connective tissue. 5)
Epithelium has a high regenerative capacity. Some epithelia are exposed to friction and their surface cells rub off. Others are damaged by hostile substances in the external environment (bacteria, acids, smoke). If and when their apical-basal polarity and lateral contacts are destroyed, epithelial cells begin to reproduce themselves rapidly. As long as epithelial cells receive adequate nutrition, they can replace lost cells by cell division.
Naming of Epithelia based on the number of cell layers:
Consist of a single cell layer.
Usually found where absorption, secretion, and filtration occur and are usually very thin. 2)
Consist of two or more cell layers stacked one on top of the other
Common in high-abrasion areas where protection is important such as the skin surface.
Stratified epithelia are named according to the shape of the cells in the apical layer.
More durable than simple epithelia.
Main role is...
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