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CHAPTER 33 A NIMAL O RGANIZATION AND H OMEOSTASIS Chapter Outline 33.1 Types of Tissues A. Levels of Organization 1. The levels of organization are: cells, tissues, organs, and organ systems. 2. The structure and function of each level depends on structure and function of organ, tissue, and cell type. B. Four Major Types of Tissue 1. Epithelial tissue covers body surfaces and lines body cavities. 2. Connective tissue binds and supports body parts. 3. Muscular tissue causes body parts to move. 4. Nervous tissue responds to stimuli and transmits impulses. C. Epithelial Tissues 1. Epithelial tissue forms a continuous layer over the body surfaces including inner cavities. 2. There are three types of epithelial tissue. a. Squamous epithelium is composed of flat cells (e.g., air sac linings of lungs, walls of capillaries). b. Cuboidal epithelium has cube-shaped cells. c. Columnar epithelium has elongated cells that resemble pillars or columns (e.g., small intestine). 3. Epithelium varies in the number of cell layers. a. Simple epithelium has one cell layer; all cells contact a basement membrane. b. Pseudostratified epithelium appears layered but actually, all cells contact the basement membrane. c. Stratified epithelium is composed of more than one layer of cells. 4. Epithelial cells can have cilia. a. Ciliated epithelium cells are covered with cilia (e.g., lining of human respiratory tract). b. Cilia can bend and move material over the surface of the epithelium. 5. Secretory epithelia can be unicellular or have multicellular glands. a. Glands are a single cell or a group of cells that secrete products into the lumen of or onto the lining of a tube or cavity, into blood, or to outside of the body; they are classified in two types: 1) Exocrine glands secrete their products into ducts or directly into a tube or cavity. 2) Endocrine glands secrete their product directly into the bloodstream. 6. Epithelium forms the outer layer of skin of animals. 7. Epithelial tissue cells are packed tightly; they join to one another in one of three ways: a. Tight junctions have plasma proteins extending between neighboring cells to bind cells tightly. b. Adhesion junctions have cytoskeletal elements joining internal plaques in neighboring cells. c. Gap junctions form when two identical plasma membrane channels of neighboring cells join so that ions and small molecules pass between cells. D. Connective Tissues 1. Connective tissue binds structures together, provides support and protection, fills spaces, stores fat, and forms blood cells. 2. Connective tissue provides source cells for muscle and skeletal cells in animals that regenerate parts. 3. Connective tissue cells are separated widely by a matrix, a noncellular material between cells. 4.
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