chapter 4

• Tissue – group of specialized cells and the extracellular substances surrounding them
• Histology


  Microscopic study of tissue
• Changes in tissues can result in development, growth, aging, trauma, or disease
• Four basic tissue types

  • Epithelial
  • Connective
  • Muscle
  • Nervous
• Epithelial tissue


  • Covers and protects surfaces, both outside and inside the body
• Epithelial tissue


  • Mostly composed of cells, very little extracellular matrix between them
  • Covers body surfaces and form glands that are derived developmentally from body surfaces
  • Distinct cell surface with a free/apical surface, lateral surface attached to other cells, and basal surface attached to a basement membrane
  • Specialized cell contacts bind adjacent epithelial cells together and to the extracellular matrix of the basement membrane
  • Blood vessels in the underlying connective tissue do not penetrate the basement membrane to reach the epithelium
  • Has the ability to replace damaged cells with new epithelial cells
• Functions of epithelia


  • Protecting underlying structures
  • Acting as a barrier
  • Permitting the passage of substances
  • Secreting substances
  • Absorbing substances
• Classification of epithelia based on number of cell layers

  • Simple epithelium - single layer
  • Stratified epithelium - more than one layer
  • Pseudostratified columnar epithelium - special type of simple epithelium
• Classification of epithelia based on idealized shapes

  • Squamous - flat cells
  • Cuboidal - cube-shaped cells
  • Columnar - tall, thin cells

  
• Major types of epithelial tissues and their distribution

  • Simple squamous epithelium
  • Simple cuboidal epithelium
  • Simple columnar epithelium
  • Pseudostratified columnar epithelium
  • Stratified squamous epithelium
  • Stratified cuboidal epithelium
  • Stratified columnar epithelium
  • Transitional epithelium

  
• Simple epithelium


  • Found in organs that primarily function to move materials like diffusion, filtration, secretion, and absorption
• Stratified epithelium


  • Found in areas of the body where abrasion can occur, adapted for protective function
• Free surface of epithelial cells

  • Can be smooth or lined with microvilli or cilia
  • Smooth free surface reduces friction as material moves across it
• Cell connections in epithelial tissue

  • Desmosomes - mechanical links that bind cells together
  • Hemidesmosomes - anchor cells to the basement membrane
  • Tight junctions - bind adjacent cells together and form permeability barriers
  • Adhesion belt - weak glue that holds cells together
  • Gap junctions - allow small molecules and ions to pass between cells
• Glands


  • Secretory organs composed primarily of epithelium with a supporting network of connective tissue
  • Develop infoldings or outfoldings of epithelium in the embryo
• Types of exocrine glands

  • Simple glands - single, nonbranched duct
  • Compound glands - multiple, branched ducts
  • Tubular glands - secretory regions shaped as tubules
  • Acinar or Alveolar glands - shaped in saclike structures
• Types of exocrine secretion

  • Merocrine secretion - release of secretory products by exocytosis
  • Apocrine secretion - release of secretory products as pinched-off fragments of the gland cells
  • Holocrine secretion - shedding of entire cells
• Connective tissue is a diverse primary tissue type that makes up part of every organ in the body

  
• Functions of connective tissue

  • Enclosing and separating other tissues
  • Connecting tissues to one another
  • Supporting and moving parts of the body
  • Storing compounds
  • Cushioning and insulating
  • Transporting
  • Protecting
• Cells of connective tissue

  • Osteoblasts - form bone
  • Osteocytes - maintain bone
  • Osteoclasts - break down bone
  • Fibroblasts - form fibrous connective tissue
  • Fibrocytes - maintain fibrous connective tissue
  • Chondroblasts - form cartilage
  • Chondrocytes - maintain cartilage
  • Macrophages - ingest foreign substances
  • Mast cells - release chemicals that promote inflammation
• Extracellular matrix of connective tissue

  • Consists of protein fibers, ground substance, and fluid
• Functions of compounds


  • Cushioning and insulating
  • Transporting
  • Protecting
• Blasts


  Create the matrix
• Cytes


  Maintain the matrix
• Clasts


  Break down the matrix for remodeling
• Cells of connective tissue

  • Osteoblasts - form bone
  • Osteocytes - maintain bone
  • Osteoclasts - break down bone
  • Fibroblasts - form fibrous connective tissue
  • Fibrocytes - maintain fibrous connective tissue
  • Chondroblasts - form cartilage
  • Chondrocytes - maintain cartilage
  • Macrophages - large white blood cells that ingest foreign substances
  • Mast cells - release chemicals that promote inflammation
• Major components of extracellular matrix

  • Protein fibers
  • Ground substance - nonfibrous protein and other molecules
  • Fluid
• Collagen fibers


  Very flexible but resist stretching
• Reticular fibers


  Very fine, short collagen fibers that branch to form a supporting network
• Elastic fibers


  Ability to return to their original shape after being stretched or compressed, giving tissue an elastic quality
• Proteoglycans


  Large molecules that consist of a protein core attached to many long polysaccharides, trap large quantities of water between the polysaccharides, which allows them to return to their original shape when compressed or deformed
• Types of connective tissue

  • Embryonic
  • Adult connective tissue

  
• Types of loose connective tissue

  • Areolar - consists of collagen fibers and a few elastic fibers
  • Adipose - consists of adipocytes, or fat cells, which contain large amounts of lipid for energy storage
  • Reticular - forms the framework of lymphatic tissue

  
• Types of dense connective tissue

  • Dense collagenous - has an extracellular matrix consisting mostly of collagen fibers
  • Dense elastic - has abundant elastic fibers among its collagen fibers

  
• Types of cartilage


  • Hyaline - most abundant type, covers ends of bones where they form joints
  • Fibrocartilage - has more collagen than hyaline, found in disks between vertebrae and some joints
  • Elastic - contains elastic fibers, found in external ear, epiglottis, and auditory tube
• Types of bone


  • Spongy - has spaces between trabecular plates
  • Compact - more solid, with almost no space between many thin layers of mineralized matrix
• Blood


  Unique due to the matrix being liquid, enabling blood cells and platelets to move through blood vessels

  
• Muscle tissue

  • Main function is to contract and shorten, making movement possible
  • Length is greater than the diameter
  • Sometimes called muscle fibers because they often resemble tiny threads