tissue from seeleys

• A tissue is a group of cells with similar structure and function,

  along with the extracellular substances located between the cells.
• Histology is the study of tissues.
• Functions of Epithelia

  1. Protecting underlying structures.
  2. Acting as a barrier.
  3. Permitting the passage of substances.
  4. Secreting substances.
  5. Absorbing substances.
• Epithelia are classified according to the number of cell layers and the shape of the cells.
• Simple epithelium has one layer of cells,
• stratified epithelium has more than one layer of cells
• Pseudostratified columnar epithelium is simple epithelium that appears to have two or more cell layers.
• Transitional epithelium is stratified epithelium that can be greatly stretched.
• Simple epithelium is involved with

  • diffusion
  • secretion
  • 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.
• A smooth, free surface reduces friction.
• Microvilli increase

  surface area,
• cilia move materials over the cell surface.
• Tight junctions bind adjacent cells together and form a permeability barrier.
• Desmosomes mechanically bind cells together,
• hemidesmosomes mechanically bind cells to the basement membrane.
• Gap junctions allow intercellular communication.
• A gland is a single cell or a multicellular structure that secretes.
• Exocrine glands have ducts,
• endocrine glands do not have ducts
• Connective tissue has an extracellular matrix consisting of protein fibers, ground substance, and fluid.
• Collagen fibers are flexible but resist stretching;
• reticular fibers form a fiber network
• elastic fibers recoil.
• Connective tissue cells that are blast cells form the matrix, cyte cells maintain it, and clast cells break it down.
• Functions of Connective Tissue

  1. Enclosing and separating other tissues.
  2. Connecting tissues to one another.
  3. Supporting and moving parts of the body.
  4. Storing compounds.
  5. Cushioning and insulating.
  6. Transporting.
  7. Protecting.
• Areolar connective tissue is the “packing material” of the body; it fills the spaces between organs and holds them in place.
• Adipose tissue, or fat, stores energy; also pads and

  protects parts of the body and acts as a thermal insulator.
• Dense connective tissue has a matrix consisting of either densely packed collagen fibers or densely packed elastic fibers
• densely packed collagen fibers (in tendons, ligaments, and the dermis of the skin)
• Reticular tissue forms a framework for lymphatic structures.
• densely packed elastic fibers (in elastic ligaments and the walls of arteries).
• Cartilage provides support and is found in structures such as the disks between the vertebrae, the external ear, and the costal cartilages.
• Bone has a mineralized matrix and forms most of the skeleton of the body.
• Blood has a liquid matrix and is found in blood vessels.
• Muscle tissue is specialized to shorten, or contract.
• The three types of muscle tissue are skeletal, cardiac, and smooth muscle.
• Skeletal Muscle - fibers appear striated (banded); cells are large, long, cylindrical, with many nuclei


  for Movement of the body; under voluntary control