Anatomy: Epithelium and Connective Tissue Quiz

Types of Tissues

• Tissues are groups of cells with similar structures and functions
• Four main types exist: epithelial, connective, muscle, and nervous
• Most organs comprise all four tissue types

Epithelial Tissue

• Forms coverings and linings
• Characteristics:
  • Closely packed cells with strong adhesions
  • Little intercellular substance
  • Cells rest on a basement membrane
  • No blood vessels pass between cells; nerves do
  • Nutrient supply from underlying connective tissue
  • Continuously degenerates and regenerates
• Embryological origin:
  • Ectodermal: epidermis of skin
  • Endodermal: lining of blood vessels and GI tract
  • Mesodermal: lining of renal tubules
• Types of covering epithelium:
  • Simple epithelium: single layer of cells, all cells reach basement membrane
  • Stratified epithelium: more than one layer of cells, only one layer reaches basement membrane
• Types of simple epithelium:
  • Simple squamous epithelium: thin cells, bulging nuclei; lining of blood vessels, lung alveoli, outer layer of Bowman's capsule
  • Simple cuboidal epithelium: cubical cells, central round nuclei; renal tubule, thyroid gland
  • Simple columnar epithelium: column-like cells, basal and oval nuclei; secretory (stomach), absorptive (intestine), ciliated (uterus and fallopian tube)
  • Pseudostratified columnar epithelium: overcrowded columnar cells, all reach the basal lamina but not the surface, nuclei at various levels; ciliated (trachea and bronchi), non-ciliated (large ducts of glands)
• Types of stratified epithelium:
  • Stratified squamous epithelium:
    • Non-keratinized type: basal layer = columnar/cuboidal, middle = polyhedral, top = flat/squamous cells; mouth cavity, esophagus, vagina
    • Keratinized type: basal = columnar/cuboidal, middle = polyhedral, top = squamous cells, layers of keratin protein on upper surface; skin
  • Transitional epithelium (urothelium): specialized for stretch in urinary tract; non-distended = 4-5 layers, columnar/cuboidal basal, polyhedral middle, umbrella cells (dome-shaped) top; distended = 2-3 layers, cuboidal basal, flattened intermediate and top layers
• Glandular epithelium:
  • Classified by presence/absence of duct:
    • Exocrine glands: have ducts (salivary glands)
    • Endocrine glands: lack ducts (thyroid, pituitary glands)
    • Mixed glands: have both (pancreas, liver)
  • Classified by branching of duct:
    • Simple glands: not branched (gastric glands)
    • Compound glands: branched (salivary glands)
  • Classified by secretory part:
    • Number:
      • Unicellular glands: single-celled (goblet cells)
      • Multicellular glands: multiple-celled (salivary glands)
    • Shape:
      • Tubular glands
      • Alveolar (acinar) glands: flask-shaped
  • Classified by secretion:
    • Mucous glands: viscous mucus, poor enzymes (goblet cells)
    • Serous glands: watery solution, rich in enzymes (parotid gland)
    • Mucoserous glands: both types (submandibular gland)
    • Sweat glands: skin
    • Oily glands: fatty secretion (sebaceous glands)
    • Waxy glands: waxy secretion (ceruminous glands of ear canal)
• Neuroepithelium: special type of epithelium modified to sense external stimuli
  • Sites: taste buds (tongue), hearing (inner ear), smell (olfactory mucosa), vision (retina)
  • Structure: sensory cells (tall with hairlets), supporting cells (support sensory cells), basal cells (precursors to sensory and supporting cells)
• Apical membrane specializations:
  • Cilia: hair-like structures; move mucus/fluid
  • Microvilli: finger-like projections; increase surface area for absorption
  • Stereocilia: similar to microvilli, but much longer; increase surface area for absorption

Connective Tissue

• Connective tissue supports and physically links tissues and cells
• Development: from embryonic mesoderm
• Interstitial fluid acts as diffusion medium for nutrients and waste
• General structure:
  • Cells
  • Extracellular matrix (ECM):
    • Fibers: collagen, reticular, elastic
    • Ground substance
• Connective tissue cells (types):
  • Fixed (resident): mesenchymal cells, fibroblasts, adipocytes, macrophages
  • Free (wandering): mast cells, plasma cells, leucocytes (WBCs)
• Types of connective tissue:
  • Connective tissue proper:
    • Loose (areolar)
    • Dense (irregular, regular, elastic)
    • Adipose (fat)
  • Embryonic:
    • Mesenchymal
    • Mucoid
  • Specialized:
    • Cartilage
    • Bone
    • Blood
• Types of Connective tissue fibers:
  • Collagen: abundant, strong, resists tearing (type I, type II)
  • Reticular: supporting structure of parenchymal organs (e.g., liver, endocrine glands, lymphoid organs)
  • Elastic: stretchy fibers, found in organs needing flexibility (e.g., walls of arteries, bronchial tree)
• Ground substance: amorphous gel-like material, in spaces between cells and fibers; acts as a diffusion medium and barrier
  • Components: water, GAGs, proteoglycans, multiadhesive glycoproteins