Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Tissues and a Introduction to the Epithelium Levels of Organization atoms→molecules→organelles→cells →tissues In the body, tissues can be classified into the following functions: Epithelial – cover 1 Connective – support 2 Movement – muscle 3 Control – nervous 4 Epithelial Tissues • Epithelial cells can be classified into 2 types, those that cover surfaces and cavities and those that form a glandular function. Epithelial tissues have the following functions: • • • • • • Protection Absorption Filtration Excretion Secretion Sensory Reception Characteristics of epithelial tissues: • Epithelial cells have an upper or free surface. Characteristics of epithelial tissues: • Epithelial cells have an upper or free surface. • This is known as the Apical Surface Polarity • The apical surface can be modified by microvilli or cilia. • Microvilli are seen with cells associated with absorption. Polarity • The microvilli can be so thick that it can be described as a brush boarder. Polarity • The bottom side of the epithelial cell is called the basal surface. • It is supported by a non cellular, adhesive sheet called the basal lamina. Specialized Contacts • Epithelial cells have contact with each other. • These lateral contacts are the desmosomes and tight junctions. Specialized Contacts • The tight junction forms an impermeable junction between each cell and thus prevents diffusion between the cells. Specialized Contacts • The desmosomes help hold the cell’s shape with anchoring junctions scattered between each cell. Connective Tissue Support • The basilar surface attached to a connective tissue net work. • There are two parts. The first is the basal lamina secreted from the epithelial cell. • The second is the reticular lamina that is made of collagen which is produced by fibroblasts. Connective Tissue Support • Together the basal lamina and reticular lamina form the basement membrane. • This forms the foundations which anchor the epithelial cells. Avascular but Innervated • Epithelial cells do not have a blood supply • They depend on diffusion for the delivery of nutrients and removal of wastes. • They do have a nerve supply, innervated, for sensory function. Regeneration • Do to their protective function; epithelial cells need to be continually replaced. • Mitotic figures are not uncommon. Cancer • Many cancers are of epithelial origin. • The greater the mitotic index, the greater the chance of cancer. Cancer Types Cancer Types • Lung cancer caused by smoking typically starts in the bronchial epithelium 1 Picture & 1000 words