CH4

Reviewer: Tissues and Their Functions

Histology:

  • Microscopic study of tissue structure

Epithelial Tissue:

  • Covers external and internal surfaces
  • Has a basement membrane, little extracellular matrix (EM), and no blood vessels

Functions of Epithelial Tissues (PAPSA):

  1. Protecting underlying structures
  2. Acting as a barrier
  3. Permitting the passage of substances
  4. Secreting substances
  5. Absorbing substances

Classification of Epithelium: According to Layers:

  1. Simple Epithelium - single layered
  2. Stratified Epithelium - multi-layered
  3. Pseudostratified Columnar Epithelium - single layered but appears stratified
  4. Transitional Epithelium - stratified and can be greatly stretched

According to Shape:

  1. Squamous - flat
    • Non-keratinized: moist, found in the deepest and outermost layers
    • Keratinized: dry, composed of dead cells containing keratin
  2. Cuboidal - cube-like
  3. Columnar - tall and thin

Functional Characteristics:

  • Simple Epithelium: diffusion, filtration, secretion, or absorption; found in organs to move materials
  • Stratified Epithelium: protection
  • Squamous Cells: diffusion and filtration
  • Cuboidal and Columnar Cells: secretion and absorption

Free Surfaces:

  • Smooth free surface: reduces friction
  • Microvilli: increase the free surface area
  • Cilia: propel materials
  • Goblet Cells: specialized mucus-producing cells

Cell Connections:

  • Tight Junctions: bind adjacent cells together and form permeability barriers, preventing the passage of materials between epithelial cells
  • Desmosomes: mechanical links that bind cells together
  • Hemidesmosomes: anchor cells to the basement membrane
  • Gap Junctions: allow small molecules and ions to pass

Glands:

  • Exocrine: secrete substances through ducts
    • Unicellular
    • Multicellular
    • Simple: non-branched
    • Compound: branched
      • Tubular (straight or coiled)
      • Acinus (grape-like) or Alveolus (small cavity)
  • Mode of Secretion:
    • Merocrine: products are released without the loss of cellular material (e.g., pancreas)
    • Apocrine: secretory products are released as fragments (e.g., mammary glands)
    • Holocrine: shedding of entire cells (e.g., sebaceous glands)
  • Endocrine: release hormones directly into the blood

Connective Tissue:

  • Contains large amounts of extracellular matrix (EM)

Functions of Connective Tissue (EC2S2PT):

  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

Cells of Connective Tissue:

  • Blast (germ): forms the matrix
  • Cyte (cells): maintains the matrix
  • Clast (break): breaks down the matrix
  • Adipocytes: contain a large amount of lipids
  • Macrophages: white blood cells that move and ingest foreign substances
  • Mast Cells: play an important role in inflammation
  • Mesenchymal Cells: have the potential to differentiate and form adult cell types

Extracellular Matrix:

  • Protein Fibers:
    • Collagen Fibers: flexible but resist stretching
    • Reticular Fibers: fine, branching support network
    • Elastic Fibers: coiled, can