tissues

• Tissue


  A group of cells with similar structure and function plus the extracellular substance surrounding them
• Extracellular substance in tissues

  • Large amounts in connective tissue
  • Very small amount in epithelial tissue
  • Huge amount in nervous tissue
• Extracellular matrix


  The extracellular substance located in between the cells
• Histology


  The study related to tissues
• Types of tissues in the human body

  • Epithelial
  • Connective
  • Muscle
  • Nervous
• Epithelial tissues


  • Form covering or lining of body cavities, coverings of body surfaces, and lining of hollow cavities
  • Connective tissue makes up part of every organ in the body and its primary function is for support
  • Muscle tissue is the only tissue capable of contraction or shortening, hence it makes movement possible
  • Nervous tissue is responsible for coordinating and controlling many body activities
• Endothelial tissue


  A modified epithelial tissue that lines the blood vessels
• Glands classified under epithelial tissue

  • Exocrine glands
  • Endocrine glands
• Characteristics of epithelial tissues

  • Mostly composed of cells with very little extracellular matrix
  • Cover and protect body surfaces
  • Have an exposed free surface and a basal surface attached to a basement membrane
  • Have special cell connections and matrix attachments
  • Are avascular (have no significant blood supply)
  • Are capable of regeneration
• Functions of epithelial tissues

  • Protect underlying surfaces
  • Act as a barrier that selectively permits passage of substances
  • Secrete substances (in glandular tissue)
  • Absorb substances (e.g. in stomach and intestine lining)
• Classifications of epithelial tissues based on number of layers

  • Simple
  • Stratified
  • Pseudostratified
  • Transitional
• Classifications of epithelial tissues based on cell shape

  • Squamous
  • Cuboidal
  • Columnar
• Simple squamous epithelium


  Single layer of flat, thin cells
• Functions of simple squamous epithelium

  • Diffusion, filtration, secretion, protection against friction
  • Found in lining of blood vessels (endothelium)
• Simple cuboidal epithelium


  Single layer of cube-like cells
• Functions of simple cuboidal epithelium


  • Secretion, absorption
  • Found in kidney tubules and glands
• Simple columnar epithelium


  Single layer of tall, narrow cells
• Characteristics of simple columnar epithelium

  • Presence of goblet cells containing mucus
  • Most are ciliated (have hair-like projections on the free surface)
• Function of cilia in columnar epithelium


  Act as a conveyor belt to move particles on the surface
• Columnar epithelium


  Single layer of tall, thin and narrow cells
• Columnar epithelium


  • Has tiny hair-like projections called cilia on the surface
  • Cilia function to move particles and mucus like a conveyor belt
• Goblet cells


  Cells that produce mucus
• Pseudostratified columnar epithelium


  Appears to have multiple layers but is actually a single layer of cells, some of which reach the free surface while others do not
• Pseudostratified columnar epithelium, like simple columnar epithelium, contains goblet cells and has cilia on the free surface
• Stratified epithelium


  Composed of multiple layers of cells
• Stratified squamous epithelium


  Composed of several layers of cells, with the top layer being flattened and squamous
• Types of stratified squamous epithelium

  • Non-keratinized
  • Keratinized
• Non-keratinized stratified squamous epithelium

  Cells retain nucleus and cytoplasm, found in moist areas like mouth, esophagus, cornea
• Keratinized stratified squamous epithelium

  Top layer of cells are dead and made of keratin protein, found in skin
• Functions of stratified squamous epithelium

  • Protects against abrasion
  • Forms barrier against infection
  • Reduces water loss
• Transitional epithelium


  Composed of stratified epithelium where cells change shape from cuboidal to flat when the organ they line (e.g. urinary bladder) is stretched or relaxed
• Functions of epithelial tissues

  • Protect underlying structures
  • Act as a barrier
  • Permit passage of substances
  • Secrete substances
  • Absorb substances
• Connective tissue


  Diverse tissue type that makes up part of every organ, characterized by cells separated by abundant extracellular matrix
• Extracellular matrix of connective tissue

  • Composed of protein fibers (collagen, reticular, elastic), ground substance (non-fibrous proteins), and fluid
• Loose connective tissue


  Contains fewer fibers and more ground substance
• Types of loose connective tissue

  • Areolar
  • Adipose
  • Reticular
• Areolar connective tissue


  Fine network of mostly collagen fibers with spaces between the fibers and cells
• Adipose tissue


  Composed of fat-filled adipocytes with little extracellular matrix
• Reticular tissue


  Loose tissue made up of a fine network of reticular fibers, forms a framework for lymphatic and hematopoietic tissues
• Dense connective tissue


  Contains more fibers and less ground substance than loose connective tissue