PNB Lecture Outline 3

PNB Lecture Outline 3 - PNB 2264 Fall 2008 Kimball Lecture...

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PNB 2264 Fall 2008 Kimball Lecture Outline 3 HISTOLOGY: THE STUDY OF TISSUES (CH. 4 M- up through p. 103 for now) I. Introduction A. Cells are organized into four main tissue types. 1. Epithelium 2. Connective Tissue 3. Nervous Tissue 4. Muscle II. Epithelium A. Overview • Covers surfaces; lines inside of organs and body cavities B. Characteristics of Epithelial Tissue • Cellularity: Composed almost entirely of cells and are bound closely together by different cell junctions • Polarity: Apical surface (free, top surface) exposed to external or internal environment and basal surface (fixed bottom surface) attached to the underlying connective tissue • Attachment: Epithelial layer bound to a thin basement membrane • Avascularity: Lack blood vessels, nutrients obtained through apical surface or diffusion through basal surface • Innervation: Detect changes at the surface • High regeneration capacity: Damage/lost epithelial cells are replaced quickly because they have a high regeneration capacity C. Functions of the Epithelial Tissue • Physical protection: Protect exposed and internal surfaces • Selective permeability: regulate the movement of materials in and out of the cells • Secretions: Produce specialized secretions (glandular epithelium) • Sensations: Nerve ending detect changes in the environment at the surface and supply info to the nervous system D. Specialized Structure of the Epithelial Tissue 1. Basement membrane • Consists of two layers; basal lamina and reticular lamina • Provides physical support for epithelium • Anchors epithelium to connective tissue • Acts as a barrier to regulate the movement of large molecule between the epithelium & underlying connective tissue 2. Intercellular Junctions (strongly bind epithelial cells) • Tight junctions: Completely attaches each cell to its neighbors (materials to move through) • Adhering junctions: Support and strengthen plasma membrane (deep within tight junctions) • Desmosomes: Attaches cell to its neighbors at potential stress points using fine web of proteins, which allows flexibility • Hemidesmosomes: Attach epithelial cells to basement membrane • Gap junctions: Gap between neighboring cells held by protein channels, providing a direct passageway for small molecules to travel between neighboring cells, rapid communication E. Classification 1. Classification by layer(s) • Simple epithelium: One layer thick, direct contact with the basement membrane (minimal stress)
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PNB Lecture Outline 3 - PNB 2264 Fall 2008 Kimball Lecture...

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