Epithelial Cell Structure
All epithelial cells have the same basic structure:
i) Apical (free) surface faces the body surface, a cavity, the lumen, or duct. ii) Lateral surfaces face the adjacent cells on each side. Lateral surfaces may contain cell junctions. iii) Basal surface is opposite of the apical surface. The deepest layer. Note: In multi-layer epithelial tissue, the apical surface is the most superficial layer and the basal surface is the deepest layer. Basement Membrane (BM): thin, extracellular layer of protein secretions from epithelial and connective tissue cells; a point of attachment and support for the epithelial layer. The BM consists of two layers: the basal lamina and the reticular lamina . The basal lamina contains proteins such as laminin and collagen. As stated earlier, the basal lamina adhere to integrins in hemidesmosomes and thus attach epithelial cells to the BM. The reticular lamina is closer to the underlying CT and contains proteins such as collagen.
There are 4 types of cells that make up epithelial tissue, differentiated by their shapes.
1. Squamous cells: Are arranged like flat floor tiles and are thin, which allows for rapid passage of substances. 2. Cuboidal cells: Are as tall as they are wide and are shaped like cubes or hexagons. They may have microvilli at their apical surface and function as either secretion or absorption. 3. Columnar cells: They are much taller than wide (columns) and protect underlying tissues. The apical surfaces may have microvilli and are also specialized for secretion and absorption. 4. Transitional cells: These change shape from flat to cuboidal and back as organs stretch and collapse.
50
Made with FlippingBook Publishing Software