histo lab m3

• Epithelial Tissue Classification:

  • Number of layers:
  • Simple = 1 layer
  • Stratified = 2 or more layers
  • Cell morphology/shape:
  • Squamous = thin cells
  • Cuboidal = cell width and thickness are similar
  • Columnar = cells taller than they are wide
• Pseudostratified epithelium is "false" stratified
• Simple Squamous Epithelium:

  • Location:
  • Mesothelium: lines digestive organs, lungs, and heart
  • Endothelium: lines lumina of the heart chambers and interior of blood/lymphatic vessels
  • Morphology:
  • Surface view (mesothelium):
  • Flat cells adhering tightly to each other to form a sheet
  • Mosaic pattern with cell boundaries
  • Centrally located nuclei
  • Transverse section:
  • Spindle-shaped cells with prominent oval nuclei
  • Thin basement membrane
  • Other locations:
  • Outer portion of Bowman’s capsule (surrounds glomerulus)
• Simple Cuboidal Epithelium:

  • Location: Excretory ducts of different organs
  • Morphology:
  • Kidney:
  • PCT has a brush border of microvilli
  • Microvilli are small, nonmotile projections that cover the surfaces of absorptive cells
• Simple Columnar Epithelium:

  • Location:
  • Digestive organs (stomach, small and large intestine)
  • 3rd part of esophagus
  • Morphology:
  • Stomach:
  • Cells are taller than they are wide
  • Apical cytoplasm has a pale appearance
  • Basal nuclei
  • Temporary folds when empty
  • Gastric pits are indentations
  • Small intestine:
  • Villi are finger-like structures that increase the absorptive surface
  • Two cell types: columnar cells with microvilli/striated borders and Goblet cells that secrete mucus
  • Other locations:
  • Uterine tubes/fallopian tubes/Oviduct (with cilia)
• Pseudostratified Columnar Ciliated Epithelium:

  • Location: Lines upper respiratory passages (trachea, pharynx, bronchi)
  • Morphology:
  • Trachea:
  • Cells appear to form several layers
  • Cilia are motile structures
  • Basal body
  • Other locations:
  • Lumina of epididymis and vas deferens (with stereocilia = nonmotile)
• Stratified Squamous Epithelium:

  • Contains multiple layers
  • Outermost cells are squamous
  • Can be keratinized or non-keratinized
  • Non-keratinized:
  • Location: Moist cavities (oral cavity, esophagus, vagina, anal canal)
  • Morphology:
  • Esophagus:
  • Live surface cells
  • Polyhedral cells in intermediate layers
  • Basal cells are cuboidal to columnar
  • Other location: Cornea
  • Keratinized:
  • Location: Skin
  • Morphology:
  • Contains nonliving, keratinized cells filled with protein called keratin
  • Layers: Stratum corneum, Stratum granulosum, Stratum spinosum, Stratum basale, Stratum lucidum (only present in palms and soles of feet)
• Stratified Cuboidal and Stratified Columnar Epithelium:

  • Location: Lines the larger excretory ducts of the pancreas, salivary glands, and sweat glands
  • Other locations: Ovarian follicles, Mammary glands
• Transitional Epithelium (Urothelium):

  • Location: Lines the minor and major calyces, pelvis, ureters, and urinary bladder
  • Morphology:
  • Bladder:
  • Can change in shape
  • Relaxed: surface cells (cuboidal) bulge out
  • "Umbrella cells"
  • Stretched: surface cells (squamous) reduced layers
• Epithelial tissue is composed of closely aggregated polyhedral cells with very little extracellular substance
• Epithelial tissue has strong adhesion and forms cellular sheets that cover the surface of the body and line its cavities
• The functions of epithelial tissue include covering and lining of surfaces (e.g., skin), absorption (e.g., intestines), secretion (e.g., glands), sensation (neuroepithelium), and contractility (myoepithelial cells)
• Covering epithelia are tissues in cells organized in layers that cover the external surface or line the cavities of the body
• Glandular epithelia are tissues formed by cells specialized to produce secretion, such as proteins, lipids, or complexes of carbohydrates and proteins
• Exocrine glands retain their continuity with the surface via a duct, while endocrine glands lose direct continuity with the surface when their ducts degenerate during development
• Lining epithelia are classified based on the number of layers and the morphologic features of the cells in the surface layer
• Classification of lining epithelia:

  • Simple = 1 layer
  • Stratified = 2 or more layers
  • Cell morphology/shape:
  • Squamous = thin cells
  • Cuboidal = cell width and thickness are similar
  • Columnar = cells taller than they are wide
  • Pseudostratified = "false" stratified
• Simple squamous epithelium is formed from one layer of squamous cells that line surfaces, facilitating various functions like movement of viscera, active transport, and secretion of biologically active molecules
• Simple squamous epithelium locations:

  • Mesothelium: lines digestive organs, lungs, and heart
  • Endothelium: lines lumina of the heart chambers and interior of blood/lymphatic vessels
• Simple cuboidal epithelium lines various ducts of glands and organs, providing sturdiness, protection, and secretion functions
• Simple cuboidal epithelium locations:

  • Excretory ducts of different organs
  • Kidney tubules
• Simple columnar epithelium is a layer of cells that are taller than they are wide, found in the small intestine for absorption and in the stomach for secretion
• Simple columnar epithelium locations:

  • Digestive organs (stomach, small and large intestine)
  • 3rd part of esophagus
• Cells with microvilli/striated borders
• Goblet cells:

  • Pale-staining cells that secrete mucus
  • Found in the uterine tubes/fallopian tubes/oviduct (with cilia) and the gastro-esophageal junction
• Oviducts:

  • Consist of ciliated and nonciliated columnar cells
  • Ciliated cells move the ovum towards the uterus
  • Non-ciliated secretory cells (peg cells) release a secretion that lubricates the tube and provides nourishment and protection to the ovum
• Gallbladder:

  • Epithelial cells have microvilli
  • Underneath the epithelium is the lamina propria
• Small intestine:

  • Non-ciliated
  • Inside of the intestine is folded and covered by villi
  • Glandular epithelium with goblet cells that secrete mucus
• Pseudostratified columnar ciliated epithelium:

  • Cell nuclei positioned in a manner suggestive of stratified epithelia
  • Lines upper respiratory passages (trachea, pharynx, bronchi)
• Trachea:

  • Ciliated pseudostratified columnar epithelium protects the lungs from irritants
  • Glandular epithelium with goblet cells that secrete mucus
• Larynx:

  • Mechanically exposed areas have stratified squamous nonkeratinized epithelium
  • Rest of the larynx has ciliated columnar pseudostratified epithelium with goblet cells
• Stratified squamous epithelium:

  • Contains multiple layers with outermost squamous cells
  • Provides protection to mechanical stress or desiccation and is found in the skin
• Non-keratinized stratified squamous epithelium:

  • Found in moist cavities like the oral cavity, esophagus, vagina, and anal canal
  • Esophagus has live surface cells, polyhedral cells in intermediate layers, and basal cells that are cuboidal to columnar
• Keratinized stratified squamous epithelium:

  • Found in the skin
  • Contains nonliving, keratinized cells filled with protein called keratin
• Stratified cuboidal and stratified columnar epithelium:

  • Lines larger excretory ducts of the pancreas, salivary glands, and sweat glands
  • Also found in ovarian follicles and mammary glands
• Transitional epithelium (urothelium):

  • Found in the excretory passages of the urinary system
  • Composed of several layers of similar cells that change shape in response to stretching or contraction