Epithelium

Epithelium

1. Characteristics of epithelium

   • 2 major forms
     • Surface epithelium
       • Consists of sheets of aggregated cells of similar type that cover all of the external surfaces and line all of the internal surfaces of the body
     • Glandular epithelium
       • Secretory cells of endocrine and exocrine glands, results from the proliferation of surface epithelial cells into underlying connective tissues
   • Functionally diverse
     • Protection
     • Absorption
     • Secretion
     • Excretion
     • Formation of barriers for selective permeability
   • Contain cytoplasmic cytokeratin filaments
     • ENDOTHELIAL CELLS DO NOT CONTAIN CYTOKERATIN
   • Cells are capable of mitosis
   • Avascular
   • Contacts a basement membrane
     • A thin sheet of extracellular matrix
     • Generally not visible with routine light-microscope sections
     • basement membrane has 2 distinct layers
       • Lamina lucida
       • Lamina Densa
   • Derived from each of the 3 embryonic germ layers

2. Surface epithelium