Notes

THREE BASIC SHAPES: SQUAMOUS cells (flattened shape and flat nucleus, fast absorption and diffusion, making thin membranes). CUBOIDAL cells (spherical nucleus, cuboidal cell shape, absorb nutrients and produce secretions like sweat). COLUMNAR cells (Elliptical nucleus, column shaped cell with hexagonal cross-section, tall, thick & cushion underlying tissues, absorb nutrients and produce secretions). Usually the form (shape and layering) of the epithelial cell is related to it's function/purpose. Producing cells take a lot of time, energy and raw materials. So in places where we lose a lot of cells (like outer skin or mouth) we have squamous cells because they are biologically cheaper. TYPES OF LAYERING: SIMPLE EPITHELIUM: one layer of cells. STRATIFIED: Multiple layers set up on top of each other, like bricks. PSEUDOSTRATIFIED: Mostly one layer but formed with cells of different shapes and sizes. The cells nuclei can be at a lot of different levels (i.e they don't lie on the same plane- different heights). So it looks like multi layered. NAMING OF A EPITHELIAL TISSUE: First name: Number of layers. Last name: Shape of its cells. Example: Simple squamous epithelium. All Epithelial cells are POLAR i.e they have distinct sides. The boundaries of many of these cells are 'Selectively Permeable'(Allowing for some level of absorption, filtration and excretion of substances). Example: tissues lining the small intestine allows absorption of nutrients through diffusion and active transport. This is what makes possible all interaction we have with the world since Epithelial cells line both the insides and outside of the body (U Tube) . GLANDULAR EPITHELIUM forms two different types of glands: ENDOCRINE glands (secrete hormones directly into the blood stream or to nearby cells) and EXOCRINE glands (secrete their juices into tubes or ducts that lead to the outside of the body.