CHAPTER 4 Tissue Level of Organization

CHAPTER 4 Tissue Level of Organization - CHAPTER 4 TISSUE...

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CHAPTER 4 TISSUE LEVEL OF ORGANIZATION Tissues —groups of similar cells and extracellular products that carry out a common function Histology —study of tissues and their relationships w organs 4 principle types of tissues: Epithelial tissue Connective tissue Muscle tissue Nervous tissue Tissue types are formed from the 3 germ layers and vary in terms of the structure of their specialized cells, cell functions, and the presence of extracellular matrix (produced by the cells that surround them) ECM is composed of varying amts of water, protein fibers, and dissolved macromolecules Epithelia, muscle, and nervous tissue have little matrix bw their cells, but conn tissue varies (this makes differences in the volume of space they occupy, relative amts of ETM components, and the consistency of it —fluid or solid) I. EPITHELIAL TISSUE A. Basic description: i. Epithelial tissue —covers or lines every body surface and all body cavities. (so it forms and internal and external lining of many organs and constitutes the majority of glands) ii. Epithelium —composed of one or more layers of closely packed cells that separates 2 different compartments. Little to no ECM b/w the cell, and no BV’s penetrating it. B. Common Characteristics of Epithelial Tissue: i. Cellularity —epithelial tissue is almost entirely composed of cells that are bound closely together (but diff junctions) and minimal amts of ECM b/w cells. ii. Polarity —every epithelium has the following surfaces 1. Apical surface —“free/top” surface exposed to either the external environment or to some internal body space 2. lateral surface —intercellular junctions 3. basal surface —“bottom” surface where the epithelium is attached to the underlying conn tissue. iii. Attachment —The basal surface is attached to a thin basement membrane (complex molecular structure produced by both the epithelium and the underlying conn tissue) iv. Avascularity —all epithelial tissues lack BVs. They get their nutrients either from directly across the apical surface, or via diffusion across the basal surface from the underlying conn tissue. v. Innervation —richly innervated to detect changes in the environment at a particular body or organ surface region. Most nerve tissue is located in the underlying conn tissue. vi. High regeneration capacity —replaced as fast as they are lost. Their apical surface that’s exposed to the environment is frequently damaged or lost by abrasion. Replacement is made via mitotic divisions of stem cells (deepest epithelial cells) located within the epithelium near its base.
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C. Functions of Epithelial Tissue (although no single epithelium performs all of them!) i. Physical protection —protects both internal and exposed surfaces from dehydration, abrasion, and destruction (physical, chemical, biological agents) ii. Selective permeability
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CHAPTER 4 Tissue Level of Organization - CHAPTER 4 TISSUE...

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