ANAT 212 (13-16)

ANAT 212 (13-16) - Lectures 13-17 Dr Reinhardt Midterm...

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Lecture 13 Major tissues in vertebrates Nerve Blood Muscle Lymphoid Epithelial Connective Cells in tissues are organized and held together by cell-cell adhesions, cell-extracellular matrix adhesions or both Epithelial and Connective Tissue In gut epithelia, the cells are very tight The C.T in the gut, however is loose (collagen is present) Classification of Cell Junction Occluding Junctions -seal cells in an epithelium, no leaking from one side to the other Anchoring Junctions - Mechanically attach cells to the neighboring cells or ECM Communicating Junctions - Mediate the passage of signals from one cell to the next -Tight junctions (vertebrates only) -Septate Junctions (invertebrates mainly) Actin Filament attachment site: -Adherens Junctions - cell-cell -Focal adhesions - cell-matrix Intermediate Filament attachment site: -Desmosomes - cell-cell -Hemidesmosones - cell-matrix -Gap junctions -Chemical synapses -Plasmadesmata (plants only) Occluding Junctions Tight Junctions in Transcellular Transport: In the gut, glucose must be taken up in the cell and further transported elsewhere by the blood Glucose conc. in lumen is usually low, high in the cell and low in the blood Thus, it must be taken up actively by the cell against a concentration gradient. Energy is provided by the Na+ driven glucose symport in the apical surface of the cell --- the energy comes from a Na gradient which drives glucose to be taken into the cell simultaneously (symport) This leads to relatively high glucose conc. in the cell Glucose must be further transported into the blood passively (because there is now a conc. gradient) by another transport protein - diffuses out of the cell by facilitated diffusion mediated by glucose carriers Thus we have two types of proteins, one active transporter on the apical side and one passive transporter on the basal surface - if they were reversed, glucose would not be able to transport properly Transport proteins in this case are confined to specific regions of the plasma membrane of the epithelial cells of the intestine Bl Na+ Lectures 13-17 Dr. Reinhardt - Midterm Material - Cell Junctions, Cell Adhesion, Extracellular Matrix - Andrea Settimi 1
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To maintain their proper positions, tight junctions seal two adjacent cells together and separate the 2 differently functioning proteins Tight junctions also prevent molecules from going btwn cells , they must enter through the cell Scales in Cell Biology Electron Microscopy Electrons emitted by a cathode Electrons accelerated by an anode The wavelength of an electron decreases as velocity increase - the higher the speed of an e- the lower the wavelength and the higher the image resolution Magnetic coils focus the image - like a number of lenses The specimen must be thin so that an electron beam may go through it (50-100nm thick) so that electrons can penetrate through Electrons are scattered when they hit any material , even air and therefore in e- microscopy an
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