L8 cell junctions and tissues

• apical domain of a cell is the _ of the cell


  top
• the lateral domain of a cell is the _ of the cell

  side
• the basal domain of a cell is the _ of the cell


  bottom
• cells elongate as they mature
• impermeable junctions are junctions that:

  prevent passage of molecules between cells e.g. tight junctions
• adhesive junctions are junctions that:


  mechanically hold cells together e.g. adheren junctions and desmosomes
• communicating junctions are junctions that:

  small molecules can passage between cells through e.g. gap junctions and chemical synapses
• tight junctions are found _ in the cellto prevent things getting through


  at the top (apical)
• adheren junctions are a couple of rows below tight junctions


  hold cells together
• hemidesmosomes anchor the cell to the substrate below
• tight junctions functions:

  • barrier/gate ->prevent molecules from leaking between adjacent cells-> regulate molecules movement
  • fence -> separate apical from basal plasma membrane (so can have different compositions in the cell -> gives rise to cell polarity
• tight junctions control paracellular movement, paracellular movement is the movement of molecules:


  between cells, trying to move from apical to basal plasma membrane
• tight junctions keep HCl in the stomach
• types of tight junction proteins:

  • transmembrane proteins
  • cytosolic proteins
• tight junction transmembrane proteins examples:

  physical barrier, adhesion, permeability
• tight junction cytosolic protein examples:

  • scaffolding
  • signalling
  • polarity
• claudin affected by the pathogen Clostridium difficile
• Occludin is affected by the pathogen Vibrio cholerae
• JAM-A is affected by the pathogen reovirus
• ZO-1 is affected by the pathogen rotavirus
• adherens junctions:


  connect cells to actin filaments, intracellular signalling regulator
• cadherins are:


  transmembrane protein, binds cells together using calcium
• cadherins are involved in:


  signal transduction
• desmosomes function:


  connect cells to intermediate filaments, structural integrity, withstand mechanical stress
• focal adhesions:


  connect cells extracellular matrix to substrate (actin filaments) using integrins
• integrins connect to extracellular matrix which then connect to actin filaments
• hemi-desmosomes function:


  connect extracellular matrix to intermediate filaments (using integrins)
• spot desmosomes structure:

  • weld cells together, inside of cell to keratin filaments
• spot desmosomes function:

  • spread stress from spot desmosome throughout the cell
• hemi-desmosomes structure:


  attach base of the cell to the basal lamina
• gap junctions structure:


  tiny pores composed of protein (connexins)

  12 connexin (6 from each cell) form junction

  permeability changed by decreasing intercellular pH or increased intracellular calcium
• gap junctions function:


  share small molecules up to 1.5 nm diameter e.g. ATP, monosaccharides, amino acids and nucleotides
• 12 connexins make up a

  connexon
• 2 connexons per cell
• 4 types of tissue:

  1. connective
  2. epithelial
  3. nervous
  4. muscle
• epithelial tissue structure:


  can be simple or stratified

  sheets of tightly packed cells

  cover outside of body, lines organs

  fastened together via desmosome junctions

  sealed via tight junctions
• epithelial tissue function:


  protect against mechanical injury

  provide barrier against microbes and fluid loss

  can have specific function for where in the body etc.
• stratified -> lots of layers
• squamous cells


  flat
• columnar cells are _ in shape


  rectangular