Epithelium

• Epithelial tissues


  Closely aggregated polyhedral cells adhering strongly to one another into a thin layer of excess cellular matrix forming cellular sheets that lined the cavities of organs of our body and cover the body surface

  
• Epithelial tissues/epithelium

  • Serve as covering, lining, and protection
  • Help by absorption
  • For secretion
• 4 basic types of tissues

  • Epithelial
  • Connective
  • Muscle
  • Nervous
• Classification and naming of epithelia

  • First name indicates number of layers (simple, stratified, or multilayer)
  • Last name describes shape of cells (tall columnar, cuboidal, or squamous)
  • Cell size and morphology are generally dictated by their function
  • Epithelial cell nuclei vary in shapes and may be elliptical, spherical, or flattened
  • Name may also include any accessory structures (microvilli, stereocilia, cilia)
• Simple squamous epithelium


  • Consists of a single layer of flattened cells usually joined by intercellular junction and resting on a basement membrane
  • Basement membrane is a thin excess cellular sheet on which the basal surface of the epithelial rest
• Simple squamous epithelium

  • Facilitates the movement of viscera
  • For the secretion of biologically active molecules
  • For active transport
  • For gas exchange
• Simple squamous epithelium

  • Lining surfaces of heart, blood vessels, serous cavities
• Simple cuboidal epithelium


  • One layer of cells whose height roughly equals their width
  • Provides protection, forms conduits for gland ducts, and maybe specialized for active secretion and absorption
• Simple cuboidal epithelium

  • Thyroid follicles, kidney (especially in collecting tubules), salivary glands/pancreas, ovaries

  
• Simple columnar epithelium


  • Consist of one layer of cells that are taller than they are wide and look like closely packed, slender columns
  • Has specialized structures on the apical surface like microvilli, cilia
• Simple columnar epithelium


  • Colon (goblet cells), fallopian tube (cilia surface), respiratory tract, vas deferens, gallbladder, small intestine (microvilli and goblet cells)
• Stratified epithelium


  • Has two or more layers of flattened cells, and it can be keratinized or nonkeratinized
  • Keratinized has keratin filaments and surface cells without nucleus and are metabolically inactive
  • Nonkeratinized has surface cells with nucleus and are metabolically active

  
• Stratified epithelium


  • Poorly suited for absorption and secretion due to thickness
  • Some are moderately permeable to water and other small molecules
• Stratified cuboidal epithelium


  Lines the excretory duct of salivary, sweat glands and ovarian follicles

  
• Stratified cuboidal epithelium


  • Functions: protection and secretion
• Stratified columnar epithelium


  Lines the conjunctiva/conjunctive
• Stratified columnar epithelium


  • Functions: protection and secretion
• Transitional epithelium


  Also called Urothelium, found only in the urinary outflow tract, with special features to make it waterproof as well as expansile
• Transitional epithelium


  • Umbrella cells: round dome shaped superficial cells
  • Mainly for urinary bladder
  • Functions: distensibility
• Transitional epithelium


  • Located in urinary tract from kidneys to the proximal part of urethra
• Pseudostratified columnar epithelium


  Irregular cells all attached to the basement membrane but give a stratified appearance due to their nuclei at different levels
• Pseudostratified columnar epithelium

  • Heavily ciliated to transport the mucus trap particles
• Pseudostratified columnar epithelium

  • Respiratory tract specifically in trachea, bronchi, and nasal cavities
• Passive transport mechanisms

  • Diffusion
  • Osmosis
  • Facilitated diffusion
• Diffusion


  Movement of molecules or ions down a concentration gradient due to their kinetic energy until they reach equilibrium
• Osmosis


  Water diffuses across a selectively permeable membrane from low to high concentration
• Facilitated diffusion


  Carrier proteins combine with substances and move them across the plasma membrane from high to low concentration
• Active transport mechanisms


  • Primary active transport
  • Secondary active transport
  • Vesicular active transport
• Primary active transport


  Substances move across the membrane against a concentration gradient by pumps or carriers that use energy supplied by hydrolysis of ATP
• Primary active transport


  • Sodium potassium ATP's pump, hydrogen ATPs pump, calcium ATP's pump
• Secondary active transport


  Ions are moved across the plasma membrane by active transport which establishes an ion concentration gradient, then ions move back down their concentration gradient by facilitated diffusion
• Secondary active transport


  • SGLT transport system, sodium-potassium-chloride pump in thick ascending limb of the kidney, sodium-calcium exchange, sodium-hydrogen exchange
• Vesicular active transport


  Endocytosis (movement of substances into a cell in vesicles) and exocytosis (materials manufactured by the cell are packed and secretory vesicle that fused with plasma membrane and release contents to the outside the cell)
• Intracellular junctions


  • Tight junction
  • Adherens junction
  • Desmosome
  • Gap junction
• Endocytosis


  The movement of substances into a cell in vesicle (towards inside); can be receptor mediated endocytosis or phagocytosis (cell eating) movement of solid particles into cell after the engulfed by pseudopods and it will form to phagosome
• Bulk phase endocytosis


  "Cell drinking" movement of extracellular fluid into a cell by enfolding plasma membrane to form a vesicle
• Exocytosis


  Materials manufactured by the cell are packed and secretory vesicle that fused with plasma membrane and release contents to the outside the cell
• Exocytosis uses ATP; proteins and other water-soluble molecules are transported out of the cell
• Tight junction


  Barrier to movement of proteins across the membranes and dividing the cell into two layers (apical; basolateral)
• Tight junction


  • Claudins, occludins, tricellulin are the most integral proteins
  • Actin microfilaments connect to cytoskeleton