Flashcards in this deck (44)

• Which tissue is the focus of this chapter page image?

  Connective tissue

  Nervous tissue

  Epithelial tissue

  Muscle tissue
  epithelium overview
• What is 'parenchyma'?

  • Parenchyma = the cells responsible for an organ's specialized functions
  parenchyma histology
• What is 'stroma'?

  • Stroma = supporting cells of an organ; usually connective tissue (except CNS)
  stroma histology
• Define 'epithelial tissue' in brief.

  • Closely aggregated polyhedral cells forming cellular sheets that line cavities and cover body surfaces
  epithelium definition
• What are main functions of epithelial tissue?

  • Cover/protect (epidermis)
  • Absorb (intestinal lining)
  • Secrete (gland parenchymal cells)
  epithelium functions
• What is the nucleus shape in columnar cells?

  • Elongated (corresponds to columnar cell shape)
  cellshape nucleus
• What is the nucleus shape in squamous cells?

  • Flattened (corresponds to squamous cell shape)
  cellshape nucleus
• What is the nucleus shape in cuboidal cells?

  • Spherical (corresponds to cuboidal cell shape)
  cellshape nucleus
• How do epithelia receive O2 and nutrients?

  • By diffusion from adjacent connective tissue across the basement membrane; epithelia are avascular
  vascularity epithelium
• What is the 'lamina propria'?

  • Connective tissue underlying epithelia of digestive, respiratory and urinary organs
  laminapropria connective
• What are 'papillae' in epithelial tissues?

  • Small invaginations of CT projecting into epithelium; increase contact area, common where friction occurs
  papillae epithelium
• What is the 'basal pole' of an epithelial cell?

  • The region of the cell adjacent to the ECM and connective tissue
  polarity basal
• What is the 'apical pole' of an epithelial cell?

  • The region of the cell that usually faces a space or lumen
  polarity apical
• What is the 'lateral surface' of cuboidal/columnar epithelial cells?

  • Surfaces adjoining neighboring cells; often folded to increase area and function
  lateral epithelium
• What is the 'basement membrane'?

  • A thin extracellular felt-like sheet on which the basal surface of epithelia rests; acts as a semipermeable filter
  basementmembrane ecm
• What is the role of hemidesmosomes?

  • Bind the basal surface of epithelial cells to the basal lamina
  hemidesmosome adhesion
• What is the 'basal lamina' and its ultrastructural thickness?

  • Fine extracellular layer seen ultrastructurally; 20–100 nm thick
  basallamina ultrastructure
• List key functions of the basal lamina.

  • Organizes integrins and membrane proteins
  • Maintains cell polarity
  • Helps localize endocytosis and signal transduction
  basallamina functions
• What are the main molecular components of the basal lamina?

  • Laminin
  • Collagen IV
  • Perlecan
  • Nidogen
  components basallamina
• How does type IV collagen assemble in the basal lamina?

  • Monomers self-assemble into two-dimensional networks of evenly spaced subunits resembling a mesh
  collagen typeiv
• What is laminin's role in the basal lamina?

  • Large glycoproteins that attach to transmembrane integrins and project through the type IV collagen mesh
  laminin ecm
• What is the function of nidogen and perlecan in the basal lamina?

  • Cross-link laminins to type IV collagen networks
  • Provide the 3-D structure of the basal lamina
  extracellularmatrix basal-lamina
• What does the reticular lamina contain and how is it bound to the basal lamina?

  • Contains type III collagen
  • Bound to the basal lamina by type VII collagen anchoring fibrils
  • Both produced by fibroblasts
  extracellularmatrix reticular-lamina
• What is the primary function of tight (occluding) junctions?

  • Form a seal at the apical end preventing paracellular flow
  • Force molecules crossing an epithelium to use the transcellular path
  celljunctions tightjunctions
• Which transmembrane proteins and cytoskeletal component are associated with tight junctions?

  • Transmembrane: occludins, claudins, ZO proteins
  • Cytoskeleton: actin filaments
  celljunctions tightjunctions
• What is the role of adherent (anchoring) junctions (zonulae adherens)?

  • Provide strong cell adhesion
  • Stabilize and strengthen occluding bands and help hold cells together
  celljunctions adherens
• Which proteins and cytoskeleton link adherens junctions?

  • Transmembrane: E-cadherin and catenin complexes
  • Cytoskeleton: actin filaments
  celljunctions adherens
• What are gap junctions and what are they made of?

  • Patches of channels for intercellular communication
  • Made of connexons (hexamers of connexins)
  • Provide little mechanical strength; no cytoskeletal attachment
  celljunctions gapjunctions
• What are desmosomes (macula adherens) attached to inside the cell?

  • Bound to intermediate filaments (keratins) forming very strong spot attachments
  • Transmembrane proteins: desmogleins and desmocollin (cadherin family)
  celljunctions desmosomes
• What do hemidesmosomes do and which proteins/cytoskeleton do they use?

  • Bind epithelial cells to the underlying basal lamina
  • Transmembrane: integrins
  • Cytoskeleton: intermediate filaments
  celljunctions hemidesmosomes
• How do focal adhesions differ from hemidesmosomes?

  • Found in migrating/reorganizing cells; smaller and more numerous
  • Integrins link directly to bundled actin filaments (not intermediate filaments)
  celljunctions focaladhesion
• Describe the structure and function of microvilli.

  • Actin-supported apical projections specialized for absorption
  • ~1 μm long, ~0.1 μm wide; can increase surface area 20–30×
  • Intestinal brush border: dense microvilli with a thick glycocalyx of enzymes
  microvilli epithelium
• What are stereocilia and how do they differ from microvilli?

  • Long, less motile apical processes on absorptive epithelia (male reproductive tract) and inner ear sensory cells
  • Much longer, may branch distally, and are less motile than microvilli
  stereocilia epithelium
• What are cilia and how long are they?

  • Long apical projections (5-10 μm)
  • Highly motile, larger than microvilli
  • Contain microtubules, not microfilaments

  
  cilia cellbiology
• What is a primary cilium and its function?

  • Non-motile apical projection
  • Enriched with receptors and signal transduction complexes
  • Detects light, odors, motion and fluid flow past the cell
  cilia sensory
• Where are motile cilia found and what is their role?

  • Abundant on cuboidal/columnar epithelial cells
  • Beat rapidly to move a current of fluid and suspend matter along the epithelium
  cilia epithelium
• What is the typical microtubule arrangement in a motile cilium axoneme?

  6+2

  9+0

  3+0

  9+2 (nine peripheral doublets + two central microtubules)
  axoneme microtubules
• What structural components maintain axoneme integrity?

  • Nexins linking peripheral doublets
  • Radial spokes and sheath protein complexes
  • Axoneme continuous with basal body in apical cytoplasm
  axoneme structure
• How are covering/lining epithelia classified by layers?

  • Simple: one cell layer
  • Stratified: two or more layers
  epithelium classification
• What is keratinization in stratified squamous epithelium?

  • Surface cells packed with keratin filaments
  • Very thin surface cells that form a protective, often anucleate layer
  keratinization epithelium
• Where is stratified squamous keratinized epithelium found and its function?

  • Mainly in the epidermis
  • Helps prevent dehydration of underlying tissue
  epidermis protection
• What are squames?

  • Metabolically inactive packets of keratin lacking nuclei
  • Contribute to barrier against water loss across the epithelium
  squames keratin
• Where is stratified squamous non-keratinized epithelium found and how do surface cells differ?

  • Lines mouth, esophagus, larynx, vagina, anal canal
  • Surface cells retain nuclei and most metabolic functions
  nonkeratinized epithelium
• What is the role of simple squamous epithelium?

  • Single layer of thin cells lining vessels and cavities
  • Regulates passage of substances into underlying tissue; often exhibits transcytosis (endothelium)
  simple endothelium