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Tissues & Junctions Lecture 34 Chapter 21 - Part 1 A) TISSUES What is tissue? • • • Biological tissue is a collection of similar cells and the intercellular substances surrounding them. • There are four basic kinds of tissue in the body: 1. epithelium 2. connective tissues – including adipose tissue, blood, bone, and cartilage 3. muscle tissue 4. nerve tissue With most multicellular organisms there are different types of cells, which are organized in to discrete groupings called tissues 21_02_tissues.jpg Plants Plant cells produce a primary cell wall followed by a secondary cell wall. The21_05_model_plantwall.jpg cell wall - which is on the outside of the plasma membrane - is made of cellulose - a polysaccharide The cell wall will only allow the cell to grow in one direction, which is dependant upon the orientation of the fibers that were laid down during the production of the primary cell wall. A) Here the plant tissue may only expand in a vertical direction 21_06_cellulose.jpg B) Here the plant tissue may only expand in a horizontal direction The celulose synthase complex, that is embedded in the plasma membrane, oozes out cellulose microfibrils 21_07_Microtubules.jpg Animals Animals have just 4 classes of tissue - connective, epithelial, nervous, and muscular (the last three are basically similar). 21_08_Extracellu_matrix.jpg Animal cells do not use cellulose. They instead have a protein extracellular matrix of collagen, which has great tensile strength. Collagen is made of many bundles of a simple polypeptide QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 21_09_Collagen_fibrils.jpg Mutations in the arrangement of these fibers may result in 21_11_elastic_skin.jpg various abnormal outcomes. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Fibroblasts are the cells that secrete collagen and also the ones that maintain 21_13_align_collagen.jpg it. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. How are cells held together? The interlinks between cells is made between collagen fibers and the actin filaments of cells using transmembrane and adaptor proteins known as integrins 21_14_Integrins_link.jpg Fibronectin - is a linker protein Epithelial sheets and cell-cell junctions 21_17_epithelial_sheet.jpg Most tissue cells have a polarized structure. They rest on the 21_18_sheet_polarized.jpg basal lamina. The basal lamina is just a layer of type IV collagen, plus other molecules. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Lung Tissue The intestine is made of two main cell types. The absorptive cells take in nutrients and the goblet cells secrete 21_20_polarize_line_gut.jpg mucus. Animal cells are held together by a number of types of cellcell junctions. 21_21_cell_cell_junction.jpg a) Tight Junctions - b) Adherens junction - c) desmosomes d) gap juctions - e) hemidesmosomes Tight junctions prevent the passage of solutes between cells. They also allow the cell to maintain discrete types of plasma membrane regions 21_22_Tight_junctions.jpg QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Tight junctions consist of proteins, for example, claudins, occludins and junctional adhesion molecules that are anchored in the membranes of two adjacent cells and interact with each other to hold the cells together and prevent other molecules from passing between them. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Adheren junctions and desmosome junctions are build on a common theme - 21_23_Cadherin.jpg they make use of transmembrane proteins that belong to the cadherin family - these molecules from adjacent cells link directly to each other. actin or intermediate filament Adheren junctions form large deposits as belts permitting adjacent cells to transmit mechanical forces 21_24_Adherens_junct.jpg Vital part in development 21_25_tube_or_vesicle.jpg Desmosomes 21_26_Desmosomes.jpg Hemidesmosomes 21_27_Hemidesmosome.jpg Gap junctions permit the free passage of small ions and small water soluble molecules to pass. However, they can be closed on demand. Plants have these too. 21_30_plasmodesmata.jpg A little perspective… The Inner Life of a Cell - Short Version Annotated Version