Epithelial-Glandular

• Tissues

  • aggregates or group of cells
  • organized to perform one or more specific functions
• germ layers

  • where tissues are derived from
• Ectoderm - outermost layer, forms the epidermis (skin), nervous system, hair, nails, teeth, lens of eye, etc.
• Mesoderm - middle layer, forms muscles, bones, blood vessels, heart, kidneys, ureters, bladder, uterus, ovaries, testes, prostate glands, etc.
• Endoderm - innermost layer, forms lining of digestive tract, lungs, liver, pancreas, thyroid gland, thymus gland, urinary bladder, etc.
• Germlayers of the Tissues

  1. Epithelial - all three
  2. Muscular - mesoderm
  3. Connective - mesoderm
  4. Nervous - ectoderm
• Epithelial Tissues and Their Basement Membrane

  • avascular tissues - do not have blood vessels, gets nutrients via diffusion
  • covers and lines body surfaces
  • glandular secretions
  • absorption
  • as receptors for the special senses
  • contractility
  • cells are close to each other by cellular junctions
  • scanty ECM
  • cells are attached to a Basement Membrane
  • functional and morphologic polarity
• domains of epithelial tissue

  • top - apical domain
  • side - lateral domain
  • bottom - basal domain (hemidesmosomes)
• Functions of Epithelial Tissues

  1. transcellular transport- diffusion of O2 and CO2 across the epithelial cells of lung alveoli and capillaries
  2. absorption - occurs via endocytosis and pinocytosis (columnar epithelium of the intestines and proximal convoluted tubules in the kidney)
  3. sensory reception (neuroepithelium)
  4. lubrication
  5. secretion - occurs via exocytosis (diff glands produce perspiration, oil, digestive enzymes and mucus)
  6. protection - abrasion and injury by the epithelial layer of skin and gall bladder
  7. filtration - lining of kidney tubules filtering wastes from blood plasma
• Apical Specializations

  1. Microvilli
  2. Cilia
  3. Stereocilia
• Microvilli

  • has glycocalyx
  • almost same length
  • finger-like extensions
  • increase surface area for absorption
  • temporary or permanent
  • appear as brush or striated border in LM
  • mostly found in columnar cells but can also be found in some cuboidal cells
  • has a terminal web
  • non motile
  • found in lining of small intestine, microtubules of the kidney
  • made of microfilaments, fibrin, and villi
• Cilia

  • longer
  • motile (sweeping)
  • elongated, whip-like, motile extensions
  • moves mucus, etc. over epithelial surface 1-way
  • rapid beating patterns to move a current of fluid
• Flagella

  • not an apical specialization
  • has microtubules
  • spermatozoa
  • extra long cilia
  • moves cell
• Microtubules assembly (9+2 - AXONEME)

  • Dynein - arms to a next microtubule
  • Kinesin
• Stereocilia

  • least common
  • can also be found in sensory organs like inner ear for hearing sensation
  • longer but less motile or non motile than microvilli
  • branched
  • seen in vas deferens and epididymis
  • not related to cilia, much more related to microvilli than cilia
• Tight Junctions: seal

  Adherent Junctions: anchoring

  Gap Junctions: communication
• Tight Junctions (zonula occludens)

  • most apical
  • formed by fusion of outer leaflets of cell's plasma membrane
  • sealing of intracellular space
  • occludin
  • claudin
  • function like fences, restricting movement of lipids and proteins
• Zonula Adherens (adherens junction/belt desmosomes)

  • surrounds entire perimeter of epithelial cells
  • provides firm belt of adhesion between two cells
  • contain adhesion molecule "E-cadherin"
• Macula Adherens (desmosome)

  • disk like
  • localized, spotlike/spot-weld junction
  • presence of desmogleins and desmocollins

  Desmoplakins -dense plaque of intercellular attachment proteins on cytoplasmic surface of each opposing cell

  Keratin - loop into and out of the desmoplakins

  Plakoglobins - links desmoplakins
• Gap Junctions (Communicating Junctions or Nexus)

  • seen in CNS, cardiac muscle, smooth muscle
  • couple adjacent cells metabolically and electronically
  • plaque like entity composed of channels called = Connexons
• Hemidesmosomes

  • cell-to-extracellular matrix junctions
  • mediate adhesion of epithelial cells to the underlying extracellular matrix
  • dense cytoplasmic plaque linked via integrins to laminins in the basal lamina
  • type VII collagen from the basal lamina extend deeper into the underlying connective tissue and insert into plaques of type IV collagen
• Basement Membrane

  • extracellular felt like supportive structure
  • composed of macromolecules
  • glycoproteins and other substance
  • stained by PAS
  • basal lamina
  • fibrous or reticular lamina

  
• Basal Lamina

  • visible only by E.M
  • type IV collagen, laminin, nidogen + perlecan (proteoglycans
  • lamina lucida (lamina rara)
  • lamina densa

  
• Occludin

  • transmembrane protein sealing of the cell
• Zonula occludens

  • first in the lateral membrane
  • prevent movement into the intercellular cells
  • junctions surrounding the cell sealing junctions
  • tight seal
• Zonula adherens

  • below the tight junctions
  • surrounds the cell
  • functions as adhesions of two cells

  E-cadherin - glue
• Macula adherens

  • "spot" in latin
  • spot like junctions

  
• Gap Junctions

  • not used for attachment or adhesion
  • found in lateral
  • used for cell to cell communication

  
• Hemidesmosomes

  • mainly for attachments
  • integrin - under the basal lamina
• []

  A) hemidesmosomes

  B) focal adhesions

  
• PAS

  • periodic acid schiff
  • carbohydrate stain, used in basement membrane
• Basement Membrane

  • extracellular felt like supportive structure
  • composed of macromolecules (glycoproteins, other substances)
  • stained by PAS
  • has two layers
  • basal lamina
  • fibrous or reticular lamina (type 3 collagen)
• Basal Lamina

  • visible only by E.M
  • composed of:
  • type IV collagen
  • laminin
  • proteoglycans = nidogen + perlecan
  • two zones:
  • lamina lucida (lamina rara) - less electron dense
  • lamina densa

  
• Classification of Epithelial Tissue

  • Cell Shape
  • squamous
  • cuboidal
  • columnar
  • transitional cell - umbrella or balloon appearance, found in the lining of the urinary bladder
  • Cell Layers
  • Simple (one layer)
  • Stratified (many layers)
• Simple Squamous Epithelium

  1. Structure - single layer of flattened cells
  2. Functions:
  3. absorption and filtration
  4. not effective protection
  5. facilitates movement of viscera
  6. active transport
  7. 3. Location
  8. pulmonary alveoli; Bowman's capsule
  9. endothelium - lining of the blood vessels
  10. mesothelium
  11. endocardium
• Simple Squamous Epithelium - Bowman's Capsule

  
• Simple Squamous Epithelium - Mesentery (rat) silver impregnation

  
• Simple Squamous Epithelium

  
• Simple Squamous Epithelium - Mesothelium

  
• Simple Squamous Epithelium - Pulmonary Alveoli