Cell Junctions KIN 2500 Tissues Supplemental Instruction Types of Tissues ANSWER KEY SI Matthew Landry mland84 lsu edu What is a tissue A group of cells that usually have a common origin in an embryo and function together to carry out specific activities Body tissues can be classified into four basic types of tissues according to their structure and function Describe their functions o Epithelial covers body surfaces and lines hollow organs body cavities and ducts it also forms glands Allows the body to interact with both internal and external environments o Connective protects and supports the body and its organs o Muscular composed of cells specialized for contraction and o Nervous detects changes in a variety of conditions inside generation of force and outside of the body and responds by generating electrical signals called nerve action potentials that activate muscular contractions or gland secretions Histology is the study of tissues Cytology is the study of cells Cell junctions are contact points between the plasma membrane of tissue cells There are five major types of junctions Tight Junctions consists of weblike stands of transmembrane proteins that fuse together the outer surfaces of two plasma membranes PMs inhibit passage of substances between cells o An example of where you could find tight junctions would be in epithelial tissues that line the stomach intestines and urinary bladder Adherens Junctions contain plaque a dense layer of proteins on the inside of the plasma membrane PM that attaches both to membrane proteins and to microfilaments of the cytoskeleton o Transmembrane glycoproteins called cadherins join the cells o This type of junction helps epithelial surfaces resist separation during various contractile activities An example of this is when food moves through the intestines Like adherens junctions desmosomes contain plaque and have transmembrane glycoproteins that extend into the intercellular space between adjacent cells membranes and attach cells to one another o However unlike adherens junctions this plaque of this junction does not attach to microfilaments It attaches to elements of the cytoskeleton known as intermediate filaments which consist of the protein keratin 1 KIN 2500 Tissues Supplemental Instruction ANSWER KEY SI Matthew Landry mland84 lsu edu o The purpose of desmosomes is to prevent epidermal cells from separating under tension and cardiac muscle tissue from pulling apart during contraction Hemidesmosomes resemble desmosomes but do not link adjacent cells o The transmembrane glycoproteins are integrins o This junction anchors cells not to each other but to the basement membrane At gap junctions membrane proteins connexins form tiny fluid filled tunnels called connexons that connect neighboring cells o Unlike tight junctions the plasma membranes are separated by a narrow intracellular gap This type of junction allows for the transportation of ions impulses and small molecules between cells Epithelial Tissue multiple layers Consists of cells arranged in continuous sheets in either single or Epithelial tissues have three major functions substances into and out of the body surface o Serve as selective barriers to limit or aid the transfer of o Release products produced by the cells onto the free o Protect against the abrasive influence of the environment The surface that faces the body surface a body cavity the lumen of an internal organ or a tubular duct is called that apical free surface This surface may contain microvilli or cilia lateral surface This surface may contain tight junctions adherens junctions desmosomes and or gap junctions surface This surface is the deepest layer of epithelial cells and adheres to extracellular material such as the basement membrane a thin extracellular layer The surface that faces the adjacent cells on either side is the The surface that is opposite of the apical surface is the basal The basement membrane is composed of two parts o Basal Lamina closer to epithelial cells Contains proteins o Reticular Lamina closer to the underlying connective such as laminin and collagen tissue and contains proteins such as collagen produced by connective tissue cells called fibroblasts 2 KIN 2500 Tissues SI Matthew Landry Supplemental Instruction mland84 lsu edu Surfaces of Epithelial Cells and the Structures and Location of the Basement Membrane ABC Diagram ANSWER KEY Classification of Epithelial Cells by Arrangement of Cells in Layers Simple A single layer of cells that function in diffusion osmosis filtration secretion or absorption Pseudostratified Appears to have multiple layers of cells All cells attach to basement membrane some cells do not extend to apical surface Can be ciliated or nonciliated Statified Consists of two or more layers of cells that protect underlying tissues in locations of considerable wear and tear Classification of Epithelial Cells by Cell Shape Squamous Thin which allows for the rapid passage of substances through them Cuboidal As tall as they are wide and are shaped like cubes or hexagons They may have microvilli at their apical surface and function in secretion and absorption Columnar Taller than they are wide Protect underlying tissues May have cilia or microvilli on apical surface Often specialized for secretion and absorption Transitional Change shape from squamous to cuboidal and back Epithelial tissue can be divided into two types covering and lining epithelium and glandular epithelium 3 KIN 2500 Tissues Supplemental Instruction ANSWER KEY SI Matthew Landry mland84 lsu edu Tissue Type Simple Squamous Epithelium Epithelial Tissues Covering and Lining Epithelia Description Single layer of flat cells that resembles a tile floor Centrally located nucleus Common Locations Function Present at sites where filtration diffusion and secretion occur Simple Cuboidal Epithelium Nonciliated Simple Columnar Epithelium Ciliated Simple Columnar Epithelium Pseudostratified Columnar Epithelium Stratified Squamous Epithelium Single layer of cube shaped cells round centrally located nucleus Single layer of nonciliated column like cells Two types of cells columnar epithelial cells with microvilli at their apical surface and goblet cells which secrete mucus Single layer of column like cells with cilia on the apical surface Goblet cells are interspersed Appear to have several layers because the nuclei are at various levels All cells attach to basement membrane some cells do not extend to apical surface Can be