TissuePart-I - Cell Polarity Epithelial cells have distinct...

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Cell Polarity Epithelial cells have distinct polarity Apical domain- is always directed toward the exterior surface or the lumen of an enclosed cavity or tube Lateral domain- communicates with adjacent cells and is characterized by specialized attachment areas. Basal domain- rests on the basal lamina anchoring the cell to underlying connective tissue. Apical Domain And Its Modifications Structural modifications Microvilli- cytoplasmic process that extend from the cell surface Stereocilia (stereovilli)- microvilli of unusual length Cilia- motile cytoplasmic processes Other specialized entities Specific enzymes (ex: hydrolases) Ion channels and carrier proteins (ex: glucose transporters) Microvilli Increases the apical surface area The number and shape of microvilli correlates with its absorptive capacity In intestine called striated border In kidney called brush border Actin in Microvilli Anchored by a binding protein called villin , located at the tip of the microvillus Filaments are crossed linked by actin-bundling protiens, fascin and fimbrin which provides strength and rigidity to microvilli Filaments extend down into the apical cytoplasm where they interact with a horizontal network of actin filaments called the terminal web Terminal web filiaments stablized and attached to cell membrane by spectrin Stereocilia (Stereovilli) Unusually long microvilli Found only in male genital ducts (epididymus, proximal ductus deferens) and the ear (sensory hair cells) Similar in structure to microvilli Unlike microvilli, erzin anchors filaments to membrane and alfa-actinin cross links filaments Absence of villin at the tip Cilia Motile cytoplasmic structures capable of moving fluid and particles along epithelial surfaces. Contain organized core of microtubules arranged in a 9+2 pattern
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Cilia Cilia Basolateral Modifications Basolateral Modifications Cell Junctions Tight Junctions (Zonula Occludens) They prevent the passage of molecules and ions through the space between cells. They block the movement of integral membrane proteins (red and green ovals) between the apical and basolateral surfaces of the cell. Tight Junctions Adherens Junctions They hold cardiac muscle cells tightly together as the heart expands and contracts. They hold epithelial cells together. They seem to be responsible for contact inhibition. Some adherens junctions are present in narrow bands connecting adjacent cells. Others are present in discrete patches holding the cells together. Adherens junctions are built from: cadherins — transmembrane proteins (shown in red) whose extracellular segments bind to each other and whose intracellular segments bind to catenins (yellow). Catenins are connected to actin filaments Gap Junctions Gap junctions are intercellular channels These permit the free passage between the cells of ions and small molecules
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TissuePart-I - Cell Polarity Epithelial cells have distinct...

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