Despite Disparate Structure and Physiologic Properties, All Organs Are Made Up of Four Basic Tissue Types
Epithelial tissue(epithelium), which covers body surfaces, lines body cavities, and forms glands
Connective tissue, which underlies or surrounds and
supports the other three basic tissues, both structurally
Muscular tissue, which is made up of contractile cells
and is responsible for movement of the body and its parts
Nervous tissue, which gathers, transmits, and integrates
information from outside and inside the body to control
the activities of the body and its parts
Each of these basic tissues is defined by a set of general morphologic characteristics or by functional properties. Each type may be further subdivided on the basis of more specific characteristics of the various cell populations as well as on the basis of intercellular substances in those cases where they present special characteristics.
In considering the basic tissues, recognize that two different definitional parameters are employed. The basis for definition of epithelium and connective tissue is primarily morphologic, whereas the basis for the definition of muscular and nervous tissue is functional. Moreover, the same variations in parameters exist in designating the tissue subclasses. For example, while muscle tissue itself is defined by its function, it is subclassified into smooth and striated categories, a purely morphologic distinction, not a functional one. Another kind of contractile tissue, though functionally muscle, is typically designated as an epithelium (myoepithelium) because of its location.
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