epithelial tissues

epithelial tissues

1. Tissues are groups of cells that are similar in structure and perform a common or related function.

   • These basic tissues are epithelial, connective, muscle, and nervous tissue
     • Most organs contain all four tissue types.

2. definition

   • Epithelial tissue, or an epithelium (plural: epithelia): a sheet of cells that covers a body surface or lines a body cavity (forming boundaries).
     • Two forms: • Covering (a surface) or lining (a cavity from inside) epithelium. • Glandular epithelium (in glands)
       • Functions: (1)protection, (2)absorption, (3) filtration, (4)excretion, (5)secretion, and (6)sensory reception

3. functional characteristics of epithelial tissue

   • Polarity (apical-basal polarity) • Two surfaces are different in terms of structure and function • Apical surface (exposed part): smooth or shows modifications; microvilli (brush border), cilia (define them and give their significance) • Basal surface (attached to underlying non-cellular adhesive connective tissue “glycoproteins and collagen fibers” called basal lamina).
     • Specialized Contacts: • Cells are tied together by tight junctions and desmosomes
       • Supported by Connective Tissue • Basement membrane: basal lamina (closer to the epithelium) and reticular lamina (belongs to the underlying CT)
         • Avascular but Innervated: no blood vessels but has nerve endings
           • Regeneration: high regenerative capacity

4. types of epithelia

   • Simple squamous
     • Kidney glomeruli (Filtration of blood to make urine) • Air sac of Lung (Gas exchange) • Lining of lymphatic vessels, heart and blood vessels (Endothelium) • Serosae (Mesothelium)
   • Simple cuboidal
     • Kidney Tubules • Duct and secretory portions of small gland • Ovary surface
   • Simple Columnar
     • Ciliated type: Small bronchi, uterine tubes and some regions of the uterus • Non ciliated type: Digestive tract (Stomach to rectum), Gallbladder, Excretory ducts of some glands
   • Pseudostratified Columnar
     • Ciliated type: Trachea and most of upper respiratory tract. • Non ciliated type: sperm-carrying ducts and ducts of large glands.
   • Stratified Squamous
     • Keratinized cells: Skin (Epidermis>> Surface cells: full of keratin and dead, Basal cells: active in mitosis). • Nonkeratinized cells: Moist linings of the esophagus, mouth and Vagina
   • Stratified Cuboidal
     • Ducts of some of larger glands (Sweat glands, mammary glands)
   • Transitional
   • stratified columnar
     • Small amount found in pharynx, the male urethra and lining some glandular ducts