Epithelial Tissue

• Tissues


  group of similar cells specialized in acommon direction to perform a common function
• 3 Primitive Germ Layers where tissue is derived from

  - ectoderm

  - mesoderm

  - endoderm
• 4 Primary Tissues

  - epithelial

  - connective

  - muscle

  - nervous
• Epithelial Tissue


  - made up of polyhedral cells compact, closely arranged and strongly attached to each other that they have scanty intercellular substances

  - attached to extracellular matrix

  - avascular or no blood vessels found among the cells

  - covers the body surfaces and those found assheets lining the organ cavities
• Characteristics of Epithelial Tissue

  - usually wet or moist (except epidermis of skin)

  - some are arranged in the form of masses (adrenal gland , parathyroid gland)

  - cells are replaced through mitosis
• Functions of Epithelial Tissue

  - Excretion

  - Protection

  - Absorption

  - Secretion

  - Sensory reception

  - Lubrication

  - Reproduction
• Structures Associated with Epithelial Tissues

  - basement membrane/ basal lamina

  - tunica propria/lamina propria
• Basement Membrane


  - where all epithelial tissues are attached

  - provides anchorage for the cells

  - Barrier limiting or regulating exchanges of macromolecules b/w CT and other tissues
• Components contribute to image of Basement Membrane

  - basal lamina

  - reticular fibers

  - ground substances
• Tunica Propria

  - support to the epithelium and vascularized CT bed providing nourishment for epithelial tissue cells

  - all epithelia has tunica propria
• Specialization of Epithelial Tissues

  1. tendency to maintain excessive contact w/ one another

  - polarity

  - cell axis

  - terminal web

  2. cell attachment and communication

  - junctional complex
• Polarity


  Molecules having uneven distribution of charges
• Cell Axis


  - imaginary line passing through the centrosome and center of the nucleus

  - Perpendicular to basal lamina
• Terminal Web


  - made of feltwork of fine filaments beneath the surface

  - provide mechanical support for ciliated or striated borders
• Tight Junction (zonula occludens)


  - most apical

  - encircle the cell

  - Adjoining cell converge and fused to close intercellular space

  - Transporting epithelium as in that of gallbladder

  - Mechanical role in maintenance of structural integrity of cells

  - Serve as tight seal preventing flow of materials b/w epithelial cells

  - Responsible for structure called- terminal bar
• Adherent Junction

  - where adjacent cells are firmly held together

  - Found b/w epithelial cells, fibroblast, smooth muscle cells and intercalated disc of cardiac muscles

  - Also responsible for terminal bar
• Desmosome


  - Disk-like structure at the surface of 1 cell that ismatch with identical structure at surface ofadjacent cell

  - Only function is as special adhesion of cells
• Hemidesmosome


  - contact b/w certain epithelial cell and basal lamina
• Gap Junction (nexus)


  - Can be mistaken for zonula occludens but opposing membranes are not fused

  - Can occur almost anywhere along lateral membranes of most epithelial cells (absent only in skeletal muscle and blood cells)

  - Well developed in tissues where cells are electrically coupled (cardiac and smooth muscles)

  - Permit transfer of small molecules (ions. Sugar, amino acids and some hormones)
• Specialized Cell Surfaces

  - microvilli

  - stereocilia

  - cilia
• Microvilli


  - Prominent in cells that function in absorption

  - Brush border serve as adaptation to enhance the surface area of membrane exposed to substances to be absorbed
• Stereocilia


  - Longer branched microvilli

  - Function is not well established but epitheliumis absorptive
• Cilia


  - Numerous motile processes larger than microvilli

  - Arranged in parallel rows projecting from surfaces of some epithelial cells

  - Surfaces serve to propel fluid or coating of mucus towards the exterior
• Flagella

  - Elongated motile structure on surface of epithelial cells, longer than cilia

  - Differ with cilia in movements and number of cells

  - Largest flagella is the mammalian spermatozoa

  - Found in the epithelia of nephrons, testes and ducts of glands
• Simple Squamous Epithelium

  - filtration and diffusion

  - endothelium, mesothelium
• Simple Cuboidal Epithelium

  nonciliated

  - tubules of kidney

  ciliated

  - bronchioles

  - thyroid glands
• Simple Columnar Epithelium

  non ciliated

  - pyloric end of stomach

  - gallbladder

  - intestines

  - rectum

  
  

  ciliated

  - fallopian tubes

  - uterine tubes
• Pseudostratified Columnar Epithelium

  non ciliated

  - male urethra

  ciliated

  - larynx

  - trachea

  - bronchi

  - oviducts
• Stratified Squamous Epithelium

  keratinized

  - epidermis of skin

  non keratinized

  - vagina

  - esophagus

  - mouth

  - anus
• Stratified Cuboidal Epithelium

  found in sweat glands
• Stratified Columnar Epithelium


  found in conjunctiva of eye
• Transitional Epithelium

  - found in urinary tract

  - distention and prevention of caustic effects of urine
• Glandular Epithelium

  - Formed by cells specialized to produce a fluid secretion different in composition from blood or intercellular fluid
• Serous Glandular Epithelium

  - pancreas

  - parotid glands
• Mucous Glandular Epithelium

  found in sublingual glands
• Mixed Glandular Epithelium

  found in submaxillary glands