Biology Chapter 40-Tissues

Biology Chapter 40-Tissues - Concept 40.2 Animal form and...

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Concept 40.2 Animal form and function are correlated at all levels of organization Animals are multicellular organisms with their specialized cells grouped into tissues. In most animals, combinations of various tissues make up functional units called organs, and groups of organs work together as organ systems. Tissues are groups of cells with a common structure and function. ° Different types of tissues have different structures that are suited to their functions. ° A tissue may be held together by a sticky extracellular matrix that coats the cells or weaves them together in a fabric of fibers. Tissues are classified into four main categories: epithelial tissue, connective tissue, nervous tissue, and muscle tissue. Occurring in sheets of tightly packed cells, epithelial tissue covers the outside of the body and lines organs and cavities within the body. ° The cells of an epithelium are closely joined and in many epithelia, the cells are riveted together by tight junctions. ° The epithelium functions as a barrier protecting against mechanical injury, invasive microorganisms, and fluid loss. The cells at the base of an epithelial layer are attached to a basement membrane, a dense mat of extracellular matrix. ° The free surface of the epithelium is exposed to air or fluid. Some epithelia, called glandular epithelia, absorb or secrete chemical solutions. ° The glandular epithelia that line the lumen of the digestive and respiratory tracts form a mucous membrane that secretes a slimy solution called mucus that lubricates the surface and keeps it moist. Epithelia are classified by the number of cell layers and the shape of the cells on the free surface. ° A simple epithelium has a single layer of cells, and a stratified epithelium has multiple tiers of cells. ° A “pseudostratified” epithelium is single-layered but appears stratified because the cells vary in length. The shapes of cells on the exposed surface may be cuboidal (like dice), columnar (like bricks on end), or squamous (flat like floor tiles). Connective tissue functions mainly to bind and support other tissues. ° Connective tissues have a sparse population of cells scattered through an extracellular matrix. ° The matrix generally consists of a web of fibers embedding in a uniform foundation that may be liquid, jellylike, or solid. ° In most cases, the connective tissue cells secrete the matrix.
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This note was uploaded on 11/04/2010 for the course BIO 107 taught by Professor Abott during the Fall '09 term at UConn.

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Biology Chapter 40-Tissues - Concept 40.2 Animal form and...

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