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18. What is the difference between basal lamina and basement membrane? 19. What are the steps of tissue preparation for light microscopy? 20. Why do we call pseudostratified columnai epithelium as pseudostrafied?
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18. The basal lamina and basement membrane are both components of the extracellular matrix that provide structural support to cells. The basal lamina is a layer of extracellular matrix secreted by the epithelial cells, while the basement membrane is a thicker layer that includes the basal lamina and additional components such as collagen and elastin fibers. The basement membrane provides additional support and anchoring for the epithelial tissue.19. The steps of tissue preparation for light microscopy are as follows: 1. Fixation: The tissue is fixed in a fixative solution to preserve its structure and prevent degradation. 2. Dehydration: The tissue is dehydrated by passing it through a series of alcohol solutions with decreasing concentrations. 3. Clearing: The dehydrated tissue is then cleared using a solvent such as xylene or acetone to remove the alcohol and make the tissue transparent. 4. Embedding: The cleared tissue is embedded in a solid medium, such as paraffin wax, to provide support and facilitate thin sectioning. 5. Sectioning: Thin slices of the embedded tissue are cut using a microtome, typically around 5-10 micrometers thick. 6. Staining: The tissue sections are stained with a dye or a combination of dyes to enhance contrast and highlight specific cellular structures. 7. Mounting: The stained tissue sections are mounted onto glass slides and covered with a coverslip.20. Pseudostratified columnar epithelium is called "pseudostratified" because it appears to have multiple layers of cells, but in reality, all the cells are in contact with the basement membrane. The term "pseudo" means false, indicating that the appearance of multiple layers is deceptive. In pseudostratified columnar epithelium, the nuclei of the cells are at different levels, giving the illusion of stratification. However, each cell is attached to the basement membrane, and the tissue is actually a single layer of cells.