Structure+and+Function

=Function and Structure= There are numerous functions associated with epithelial, and they depend on both the location of the tissue and the structure of the tissue.
 * Protects – skin
 * Excretes - kidneys
 * Filters - kidneys
 * Absorbs - digestive lining
 * Secretes – glands
 * Forms boundaries
 * Sensory reception - contain nerve endings that pick up stimuli





**Characteristics ** Tightly packed – very little intercellular space – intercellular = in between – little in between space Tight junctions – protein molecules in membranes of adjacent cells fuse together to form an impermeable sheet Works like little snaps that fit together (ice hockey referee badge to stripy shirt) Desmosomes - adjacent cells are held together by protein filaments (linker proteins) that extend from the plasma membranes and interdigitate like the teeth of a zipper in intercellular space. Apical surface = free surface Basal surface is attached to a sheet of glycoproteins (glyco = sugar) called basal lamina Basal lamina = basement or bottom sheet <span style="color: black; font-family: 'Arial','sans-serif';">It allows for diffusion <span style="color: black; font-family: 'Arial','sans-serif';">Apical surface can have microvilli (finger like membrane extensions) to try to cram a lot of surface area into a small space <span style="color: black; font-family: 'Arial','sans-serif';">Apical surface can have cilia little sweeping hairs to trap and clear substances <span style="color: black; font-family: 'Arial','sans-serif';">Always clears toward an opening for disposal <span style="color: black; font-family: 'Arial','sans-serif';">The basement membrane is double layered <span style="color: black; font-family: 'Arial','sans-serif';">The layer closest to the epithelial cells is the basal lamina (layer or sheet) averages 40-50 nanometers (1 millionth of a millimetre) thick <span style="color: black; font-family: 'Arial','sans-serif';">Basal lamina is composed of 2 or 3 divisions (interna, densa? externa?) <span style="color: black; font-family: 'Arial','sans-serif';">Deep to the basal lamina is the reticular lamina, a layer containing a network of collagen protein fibres that belong to the underlying connective tissue <span style="color: black; font-family: 'Arial','sans-serif';">Together the 2 layers form the basement membrane <span style="color: black; font-family: 'Arial','sans-serif';">The basement membrane reinforces the epithelial sheet helping it to resist stretching and tearing and it defines the epithelial boundary **<span style="font-family: 'Arial','sans-serif';">Epithelial Tissue ** <span style="color: black; font-family: 'Arial','sans-serif';">Epith means ‘laid on’ or ‘covering’ in Latin **<span style="color: black; font-family: 'Arial','sans-serif';">Epithelial Characteristics ** <span style="color: black; font-family: 'Arial','sans-serif';">Avascular - no blood supply within it. All comes via diffusion from basement membrane. <span style="color: black; font-family: 'Arial','sans-serif';">Innervated – has a nerve supply <span style="color: black; font-family: 'Arial','sans-serif';">Regenerative – rapid regrowth by cell division

<span style="color: black; font-family: 'Arial','sans-serif';">Classifying Epithelial Tissue <span style="color: black; font-family: 'Arial','sans-serif';">Objectives and Introduction <span style="color: black; font-family: 'Arial','sans-serif';">Epithelial content