Anatomy and Physiology IWeek 4:The Tissue Level of Organization
Chapter ObjectivesThe purpose of thischapter is to:•Learn about the varioustypes of tissues and theirorigins•Discuss how cells of atissue are held together•Compare and contrastepithelial, connective,muscular, and nervoustissue•Learn about the structureand function of
Types of Tissues•Tissue: a group of cells ofsimilar type that worktogether to serve acommon function.•Epithelial-coverings of bodysurfaces, lines body cavities, andforms glands.•Connective-storage site for fat,immunity, provides body andorgans with support and protection.•Muscle-body movement andmovement of substances throughthe body.
•Cells can be heldtogether in severalways. Thesepoints of contactbetween cells arecalled celljunctions.Cell Junctions
Cell Junctions: Tight Junctions•Tight junctions:fuse adjacent cells together by forming a belt aroundthe cell.•Prevent leakage into/out of intercellular space.•Found between epithelial cells of the digestive tract.
Cell Junctions: Desmosomes•Acts like rivets through the membranes of adjacent cells usingintermediate filaments and cadherins.•Found in tissues that undergo significant mechanical stress such as thebladder and cardiac tissue.
Cell Junctions:Hemidesmosomes•Acts like rivets between thecytoskeleton of one cell to theextracellular matrix viaintermediate fibers andintegrins.•Found between keratinocytesof the epidermis and the basalmembrane.
Cell Junctions: Gap Junctions•Gap junctions: allow cells to communicate by allowing small molecules andions to pass from cell to cell.•Found in epithelia in which movement of ions coordinates function.•E.g.beating of cilia and in excitable tissues such as heart and muscle.
Cells are arranged insheetsCells are densely packedMany cell junctions arepresentEpithelial cells attach toa basement membraneEpithelial tissue isavascular but does havea nerve supplyMitosis occurs frequentlyGeneral Features of EpithelialTissue