Epithelial Tissue

Epithelial Tissue

1. Classified by layers and shape

   • Layers
     • Pseudostratified
       • Pseudostratified (Ciliated) Columnar Epithelium
         • Secrets substances, particularly mucus that traps foreign particles & sweep away by ciliary action
         • Ciliated: lines trachea, most of the upper respiratory tract Non-ciliated: in male's sperm-carrying ducts
       • 1 layer but it looks like multiple
     • Simple
       • Simple Squamous Epithelium
         • Thin, simple layer - Diffusion, filtration, secretion
         • Lining of the heart, blood vessels, lymphatic vessels, air sacs of lungs, kindneys
       • Simple Cuboidal Epithelium
         • Secretion & absorption
         • Lines kidney tubes, ovary surface, secreting portion of glands (thyroid)
       • Simple Columnar Epithelium - non ciliated
         • High levels of absorption & secretion, lubricates linings of digestive, respiratory & reproductive tracts
         • Lines Gastrointestinal tract (stomach to anus), ducts of many glands & gall bladder, goblet cells (in the nose)
       • Simple Columnar Epithelium - ciliated
         • Absorption, secretion, moves mucus (or reproductive cells) by ciliary action
         • Lines bronchioles of respiratory tract, uterine tubes, some regions of the uterus
       • Only 1 layer
     • Stratified
       • Stratified Squamous Epithelium - Keratinized
         • Protects against abrasion, water loss, UV & foreign invasion
         • Superficial layer of skin - epidermis
         • Keratin=tough protective protein
       • Stratified Squamous Epithelium - Non- Keratinized
         • Protects agains abrasion & foreign invasion
         • Lines wet surfaces: mouth, oesophagus, tongue, part of epiglottis of vagina
       • Stratified Cuboidal Epithelium
         • Rare; protection, limited secretion & absorption
         • Lines ducts of adults sweat glands, mammary glands & oesophageal glands, part of male urethra
       • Stratified Columnar Epithelium
         • Rare; protection & secretion
         • Lines male urethra, some glandular ducts, pharynx
       • Transitional Epithelium
         • Allows urinary organs to stretch & maintain protective lining, while holding fluid
         • Urinary bladder, parts of uterus & urethra
       • 2 + layers
   • Cell Shape
     • Squamous
       • Flattened shape
     • Cuboidal
       • Cube Shape
     • Columnar
       • Flattened Shape
       • Column Shape

2. Covers body surface, lines hollow organs & forms glands

3. Avascular, relays on blodd vessels of the adjecent connective tissue, hihg rate of cell division, own nerve supply

   • COVERING & LINING EPITHELIUM

4. GLANDULAR EPITHELIUM

   • Exocrine
     • Generates secretion & empties by duct onto surface
       • Sweat & oil glands
         • Sweat, oil, saliva, digestive enzymes
   • Endocrine
     • Secrets substance directly into the bloodstream
       • Pituitary gland, thyroid & parathyroid glands
         • Hormones, that regulate metabolic & physiological activities