CONTENTS HISTOLOGY FOR MEDICAL STUDENTS
ATLAS OF HISTOLOGY IMAGES

EPITHELIAL TISSUE

EPITHELIUM IS A CELLULAR LAYER ON THE BASEMENT MEMBRANE

epithelia cover the external surfaces of the body, its serous cavities, outer and inner surfaces of many
internal organs, form secretory units and line excretory ducts of exocrine glands

EPITHELIAL TISSUE TRAITS
  • cells form layers
  • there is a basement membrane
  • cells are tightly linked to each other
  • cells are polar (apical and basal parts)
  • no blood vessels
  • no intercellular matter
  • high regenerative capacity

  • CLASSIFICATION OF EPITHELIAL TISSUE
    BY ORIGIN BY LOCATION AND FUNCTION
    Ectodermal epithelia (epidermal; ependymoglial)
    Entodermal epithelia
    Coelomic nephrodermal epithelia
    Mesodermal epithelia
    Mesenchymal epithelia (angiodermal)
    Surface epithelia
    cover organs from outer and inner surfaces
    Glandular epithelia
    form secretory portions and line excretory ducts of exocrine glands
    BY STRUCTURE
    this classification is based on the main principle: cells' relationship to the basement membrane
    SIMPLE (NON-STRATIFIED) EPITHELIA STRATIFIED EPITHELIA
    all epithelial cells lie on the basement membrane not all epithelial cells lie on the basement membrane
    simple squamous

    simple cuboidal (low columnar)

    simple columnar (cylindrical):
    all epitheliocyte nuclei are on the same height from the basement membrane, for epithelium consists of monomorphic (similar) cells

    pseudostratified columnar:
    epitheliocyte nuclei are on different levels, since epithelium cellular composition is heterogeneous (e.g. goblet, large and small intercalated cells)
    villous (brush) - if epithelium possesses cells with apical microvilli
    ciliated - if there are cells with cilia

    stratified cuboidal or columnar epithelium consists of 2 or 3 layers of columnar or cuboidal cells

    stratified squamous nonkeratinized consists of three layers: basal, intermedium (spinosum), and surface

    stratified squamous keratinized - five layers are identified: basal, spinosum, granulosum, lucidum and corneum; basal and spinosum layers combine to form stratum germinativum, for these cells are capable of division

    stratified squamous epithelia possess nuclear polymorphism: nuclei of the basal layer are elongated and perpendicular to basement membrane, stratum intermedium (spinosum) nuclei are around-shaped, and superficial (granular) cell nuclei are also elongated, but parallel to the basement membrane

    transitional epithelium (urothelium) is composed of basal and superficial cells without nuclear polymorphism: all cells' nuclei are around in shape

    EXOCRINE GLANDS     consist of 2 parts: terminal (secretory) portions and excretory ducts

    CLASSIFICATION
    simple glands    have a non-branching excretory duct complex     have a branching excretory duct
    non-branched     have non-branching terminal portions branched     have branching terminal portions
    by terminal (secretory) portion type: alveolar, tubular, alveolar-tubular
    by secretory product: e.g. proteinaceous, mucous, muco-proteinaceous (mixed)


    TYPES OF SECRETION

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