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Main page | Structure | Departments | Department of Histology and Embryology | Materials for students | Modul 1 | EPITHELIAL tissue.

                                              EPITHELIAL tissue   (or epithelium   = EP. ).
EP. –  is  layer of cells,   attached to  BASEMENT MEMBRANE.    NO   blood vessels   in EP.;
NO  extracellular matrix  in EP.;  Epithelial cell is POLAR, because it has 3 surfaces with different structure: 1)APICAL surf.  It can carry SPECIAL organells: a) MICROVILLI (in small intestine, kidney) or  b) CILIA (in bronchi, trachea);   2) BASAL surf.   It attached to basement membrane;    3) LATERAL surf.  By it cells attach each to other with  “tight junctions”.
                          MORPHOLOGIC  classification of  EP.   includes 2 types of EP.:
   1) SIMPLE  EP.   ( if   ALL  cells attach to basement membrane), 
                                2) STRATIFIED   EP.    ( if    NOT all cells attach to basement membrane).
                                                                SIMPLE epithelia:
1) Simple  SQUAMOUS  EP.  includes   2  types:    A)  ENDOthelium,     B) MESOthelium.
  A) Endothelium   lines    blood  VESSELS,  lymph vessels,    heart  CHAMBERS.
Funct.:  It  secretes    anticoagulants,    preventing   intravascular blood coagulation.
 B) Mesothelium  covers  surfaces of    PLEURA,    PERITONEUM,     PERICARDIUM.
  Funct. It secretes     serous fluid,    reducing  friction.
 2) Simple CUBOIDAL EP.   It locates in RENAL tubules. Cells carry MICROVILLI. 
   Funct. --  is  H2O and ions  reabsorption.
3) Simple COLUMNAR EP.    It lines mucosa of    STOMACH,   SMALL intestine,     COLON.
 Cells in small intestine carry apical MICROVILLI, collectively named BRUSH BORDER. Funct.:
  It participate in TERMINAL digestion and monomers   absorption.
4) Simple COLUMNAR  PSEUDOstratified  CILIATED  EP.  It lines  BRONCHI , TRACHEA.
              It contains :   a) CILIATED cells ,    b) GOBLET  cs.,    c)BASAL cs. 
 Ciliated cells are tall columnar cs with apical  CILIA.   Funct.: removal of dust particles.
                                                       STRATIFIED  epithelia:
1) Stratified  squamous  NONkeratinized  EP. It  lines  ORAL cavity (tongue), ESOPHAGUS,   CORNEA. It is composed of 3 layers:1)Stratum basale .( cuboidal cells with function as origin of regeneration),  2)Stratum spinosum,  3)Layer of  squamous  cells. (cs contain nuclei and don’t contain protein keratin.   Funct. –   is protection).
2) Stratified  squamous  KERATINIZED  EP.    It is in:  skin EPIDERMIS,  HARD PALATE, GINGIVA,  CUTANEOUS ANUS.  It has 5 layers: A)Stratum basale.(contains cuboidal cells with function as origin of REGENERATION, due to active MITOSIS/proliferation), B)Stratum spinosum, C)Stratum granulosum, D)Stratum lucidum, E) Stratum CORNEUM.   Squamous  cells  in it don’t contain nuclei and contain protein  keratin.   Funct. of str. CORNEUM –   is   PROTECTION.
 3) Stratified TRANSITIONAL EP.    It lines:   renal PELVIS,   URETER,   URINARY bladder, URETHRA.
                                 GLANDS (=Gs).       It are composed of  GLANDULAR epithelium.
1)EXOcrine Gs are composed of 2 portions:   1)DUCT,       2)SECRETORY portion   (or  acinus).
 2)ENDOcrine Gs are composed of 1 portion:   SECRETORY portion  only. (it are   ductless)
                                              Morphologic classification of   EXOcrine   Gs:
1)If duct is NOT branched – gland is   SIMPLE.    2)If duct is  branched – gland is   COMPOUND.
3)If secretory portion is spherical-shaped – gland is   ALVEOLAR.  4) If secretory portion is cylindrrical-shaped – gland is TUBULAR. (for  example, sweat gland – is SIMPLE TUBULAR gl.; salivary Gs- are   COMPOUND TUBULO-ALVEOLAR   Gs.
  Glandular epithelial cells in SECRETORY portion synthetize and secrete secretory products (sweat, saliva, milk, sebum) into duct, emptying on skin surface or lumen of hollow organs.
            Mechanisms of releasing of   secretory  products   (or types of secretion)  from 
                                                                              glandular   epithelial cell:
1) MEROcrine   secretion – when cell portions are NOT pinched-off into secretory products.
                                                                                                           (parotid salivary Gs)
 2) APOcrine   secretion -   when APICAL (only) portions of cytoplasm  are  pinched-off  
                                                  into   secretory  products.
3) HOLOcrine  secretion -    when epithelial cell during secretion is COMPLETELY DESTROYED.                                                     (sebaceous Gs)
Составитель – доцент В.В. Бондаренко.
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