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L 8 Epithelium 3

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					Epithelium 3




          MD1Histology: Lecture 8
          Glandular Epithelium
    The function of glandular epithelium is secretion.

   A gland may consist of a single cell or a group of
    cells that secrete substances into ducts (tubes),
    onto a surface, or into the blood.

   All glands of the body are classified as either
    endocrine or exocrine.

   Glands that discharge their secretion onto the
    epithelial surface of hollow organs, either directly or
    through a duct, are called exocrine glands.

   Secretions of exocrine glands include mucus, saliva,
    digestive juices and earwax. Exocrine glands vary
    considerably in size, shape and complexity.

   Glands that discharge their secretions into blood
    and lymph are called endocrine glands (ductless
    glands).

   In some epithelia, individual cells secrete a
    substance that does not reach the blood stream but
    affects other cells within the same epithelium. Such
    secretory activity is referred to as paracrine. The
    secretory material reaches the target cells by
    diffusion.
                     Exocrine Glands Classification
1.   By the number of cells
         -Unicellular – one cell is the responsible for the secretion; Goblet cells
         -Multicellular – more than one cell; Most other glands
2.   By their ducts
         -Simple – duct unbranched
         -Compound – duct branches
3.   By the shape of their secretory units
         -Tubular
         -Acinar (alveolar) – flask-shaped
         -Tubuloalveolar – mixed type
4.   By their secretion
         -Mucous – mucus (mucin + water)
         -Serous – watery secretion
         -Mixed
5.   By the way they secrete

        -Holocrine – cell accumulates the product, then dies & becomes part of the
      secretion (sebaceous glands)
         -Apocrine – secretory product accumulates in apical cytoplasm, & the region is
      lost with the secretion (mammary gland)
         -Merocrine – product is created & discharged by exocytosis without loss of
      cytoplasm (most glands)
Simple glands
                  Glandular Epithelium
    Multicellular exocrine glands are
    categorized according to two criteria:
       whether the ducts of the glands are
        branched or unbranched

       by the shape of the secretory portions
        of the gland.

   If the duct of the gland does not branch, it
    is a simple gland.
   If the duct branches, it is a compound
    gland.

   Glands with tubular secretory parts are
    tubular glands; those with more rounded
    secretory portions are acinar glands.
    Some glands have both types and are
    referred to as tubuloacinar
Compound glands
***Serous, mucous & mixed acini
 The secretory cells of exocrine glands are so
   named because of the type of secretion produced
 Mucous secretions are viscous & slimy, whereas
   serous secretions are watery.
 Goblet cells, secretory cells of sublingual salivary
   glands, and surface cells of the stomach are
   mucus-secreting.

***MUCOUS GLANDS
 The mucous nature of secretion results from
   extensive glycosylation of the proteins. The
   mucinogen granules are PAS positive.
 These are dissolved during tissue preparation
   and the cytoplasm appears to be empty in H&E
   staining.
 The mucous cell nucleus lie flattened against the
   base of the cell.
          Serous gland
   Serous cells produce poorly
    glycosylated or nonglycosylated
    protein secretions.
   The nucleus is typical round or
    oval. The apical cytoplasm is often
    intensely stained with eosin.
   Serous cell containing acini are
    found in parotid gland and
    pancreas.
   Acini of some glands e.g
    submandibular, contain both
    mucous and serous cells (mixed
    acini or gland). In normal
    preparation the serous cells are
    more removed from lumen of the
    acinus and are shaped as crescents
    or demilunes ( a mixed type) at the
    periphery of mucous acinus.
Cells of exocrine glands exhibit
different mechanisms of secretions
        MYOEPITHELIAL CELLS
-several exocrine glands (sweat, lacrimal,
salivary, mammary) contain stellate or spindle-
shaped myoepithelial cells.

-These cells embrace gland acini. Located
between basal lamina and basal pole of
secretory or ductal cells.

-They are connected to each other by gap
junctions and desmosomes.

-Cytoplasm contains numerous actin, myosin
and intermediate keratin.

Function is to contract around the secretory
or conducting portion of gland and help propel
secretory products toward the exterior.
                Endocrine Glands
Cord and clump type – confluent
cords & clumps of endocrine cells
between dilated capillaries; the
storage of the product is
intracellular (adrenal medulla,
adrenal cortex)



Follicular type – groups of cells
forms a follicle with a central space
where the secretory product is
stored. When needed, the product is
taken from the follicle by the cell and
put in the capillaries (thyroid)
THE DIFFUSE NEUROENDOCRINE
SYSTEM (DNES) – (not forming group, they
are singles that can produce certain things)

The cytoplasm of cells contain either polypeptide
hormones or the biogenic amines epinephrine,
norepinephrine or 5-hydroxytryptamine
(serotonin).

They are called APUD - amino precursor uptake
and decarboxylation cells or argentaffin and
argyrophil cells because they take silver salts.

DNES are known as paracrine cells -they produce
chemical signals that diffuse into the surrounding
ECF to regulate the function of neighboring cells
without passing through the vascular system.
They also act as chemical mediators in the
nervous system.
DNES polypeptide-secreting cells have distinctive,
dense granules.

				
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posted:1/14/2011
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