Tissues

• Tissue: is a group of cells with similar structure and function, along with extracellular substances located between cells.
• Changes in tissues can result in development, growth, aging, trauma, or disease.
• Histology: is the microscopic study of tissue structure
• Epithelial: covers and protects surfaces, both outside and inside the body.
• Connective: provides support, protection, and binds other tissues together. A diverse primary tissue type that makes up part of every organ in the body.
• Muscle: allows movement by contracting to shorten or lengthen.
• Nervous: transmits information throughout the body through electrical impulses. Responsible for coordinating and controlling many body activities.
• EPITHELIAL TISSUE: Mostly composed of cells with very little extracellular matrix between them.
• EPITHELIAL TISSUE: covers body surfaces that include the exterior surface, lining of digestive, urinary, reproductive, & respiratory tracts, heart & blood vessels, and linings of body cavities.
• Distinct epithelial cell surfaces:

  
  

  • Free / Apical Surface – exposed & not attached to other cells.
  • Lateral Surface – cells attached to other epithelial cells.
  • Basal Surface – attached to a basement membrane (a specialized type of extracellular material that helps attach the epithelial cells to the underlying tissues and plays an important role in supporting & guiding cell migration during tissue repair.)
• Major Functions of Epithelia:

  
  

  • Protecting underlying structures
  • Acting as a barrier
  • Permitting the passage of substances
  • Secreting substances
  • Absorbing substances
• CLASSIFICATION OF EPITHELIUM:

  
  

  • Simple
  • Stratified
  • Pseudostratified
  • Transitional
• Simple: one layer of cells only
• Stratified: more than one layer of cells
• Pseudostratified: special type of simple epithelium; appears to be stratified but is not
• Transitional: modification of stratified epithelium that can be greatly stretched
• Shape of cells (Simple):

  
  

  • Squamous
  • Cuboidal
  • Columnar
• Shape of cells (Stratified)

  
  

  • Squamous
  • Nonkeratinized (moist)
  • Keratinized
  • Cuboidal
  • Columnar
• Shape of cells (Transitional):

  
  

  • Roughly cuboidal to columnar when not stretched and squamous-like when stretched.
• Simple Squamous: 1 layer of flat, tile-like cells, often hexagonal cells
• Simple Cuboidal: 1 layer of square-shaped cells
• Simple Columnar: 1 layer of tall, narrow cells
• Pseudostratified Columnar: 1 layer of tall, narrow cells, appears stratified but isn’t, almost always ciliated
• Stratified Squamous: many layers of flat, tile-like cells
• Stratified Cuboidal: many layers, cube-shaped; relatively rare
• Stratified Columnar: many layers, but only the surface cells are columnar; deeper layers are irregular or cuboidal in shape; relatively rare
• Transitional: special type that changes shape

  • stretched: squamous
  • not stretched: cuboidal
• Simple epithelium is involved with diffusion, secretion, or absorption.
• Stratified epithelium serves a protective role.
• Squamous cells function in diffusion or filtration.
• Cuboidal or columnar cells, which contain more organelles, secrete or absorb.
• Microvilli: increase cell’s surface area (ex: small intestines)
• Cilia: move materials across cell’s surface (ex: trachea)
• Goblet Cells: produce mucus (ex: stomach)
• Tight Junctions: bind adjacent cell together
• Desmosomes: mechanical links that bind cells
• Hemidesmosomes: bind cells to basement membrane
• Gap Junctions: most common; small channels that allow molecules to pass between cells & allow cells to communicate
• Glands: structures that secrete substances onto a surface, into a cavity, or into blood; primarily composed of epithelium, with a supporting network of connective tissue.
• Exocrine: type of gland with ducts (ex: sweat & oil glands)