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The epithelium by dandanhuanghuang

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									The epithelium
             By


      Dr. Nahed Zohdy
              &
  Dr. Ibtehag El Ghazzawy

 Professors of Hisology and
        cell biology
II Glandular Epithelium
Origin




differentiation
Types of glandular epithelium

    It is classified according to:

1- Number of cells
2- Presence or absence of a duct system
3- Mode of secretion (mechanism)
4- Nature of secretion
5- Shape of the secretory portion
6- Branching of the ducts
   Glandular epithelium

Unicellular           Multicellular
                        (e.g. exocrine pancreas)
  (e.g.Goblet cell)
       Goblet cells
• LM
Goblet cells

EM
Mechanism of Glandular
     secretions

• Merocrine
• Apocrine
• Holocrine
       Merocrine glands
• The secretions
  are released
  through
  exocytosis
Pancreas
Mode of secretion
   (apocrine)
       Apocrine glands


• The secretion Involves
  the loss of both product
  and apical cytoplasm
Mammary glands
        Holocrine gland

• The secretion
  destroys the
  cell
Sebaceous
  glands

                   Click on the
                   photo
Glandular epithelium
Nature of Glandular secretions




   (serous – paroptid gland)
Nature of Glandular secretions




     (mucous – sublingual gland)
Nature of Glandular secretions




          (mixed glands)
Nature of Glandular secretions




 (oily secretion) - sebaceous gland)
The shape of secretory portion

                     o-
Classification of Tubular Glands




Intestinal glands   Sweat glands   Fundic glands
Simple straight tubular glands
Classification of Alveolar Glands




Sebaceous glands     Tarsal glands
 Classification of Compound Glands




Liver      mammary glands   salivary glands
      Sebaceous glands

•   Multicellular
•   Exocrine
•   Holocrine
•   Secrets fatty secretions
•   Simple alveolar
Specialized type
 of epithelium
 Special types of epithelium




Neuroepithelium     Myoepithelial cells


         Germinal epithelium
Neuroepithelium (taste bud)
2. Germinal epithelium




         testis
2. Germinal epithelium




         ovary
      3- Myoepithelial cells

Sites:
• Salivary glands
• Mammary
  glands
• Sweat glands
Myoepithelial cells
       Functions of epithelium
•   Protection
•   Secretory
•   Absorption
•   Filtration and gas diffusion
•   Smooth surface (endothelium & mesothelium)
•   Sensation (neuroepithelium)
•   Contraction (myoepithelium)
•   Reproduction (germinal epithelium)
Epithelial Polarity
          Cell Surfaces
• Apical surface



• Lateral surface



• Basal surface
               Epithelial Polarity
   Apical modifications
                            Basal modifications
                            • basement membrane
                            • basal enfolding
 Apical protrusions
                                                  Lateral modifications
                                                  • cellular Interdigitations
                  Cytoplasmic modifications
                                                  • intercellular junctions




Microvilli    stereocilia     cilia

                                      Occluding     anchoring            gap
       I- Apical Modifications
1- Microvilli:
LM




Striated border (Brush border)- Small intestine
Microvilli: EM




      actin
   filaments
2- Cilia:
LM
2- Cilia:
EM
  Cilia and Microvilli (scanning EM)


micovilli
                                 cilia
3- Stereocilia:
LM

 • Long
 branching
 microvilli

 • Non motile



                  Epididymis
      Stereocilia: EM




Epididymis    Cochlea (inner ear)
Apical cytoplasmic specialization


• Ciliated cells have numerous
  mitochondria in the cell apex, close
  to the basal bodies
• These mitochondria produce ATP.
      II-Basal Modifications
1- Basal enfolding




Basal striations by LM
2- Basement membrane
Structure:
• LM:




    Basement membrane stained by   PAS stain
2- Basement membrane
Structure:
• EM
1-Basal lamina:
  Lamina lucida         Epithelial cells
  Lamina densa


2- Lamina reticularis    Connective tissue cells cells
Basement Membrane EM



       Lamina lucida

       Lamina densa

       Lamina reticularis
Basement membrane (EM)
   III- Lateral Modifications



1- cellular
  Interdigitations
   2- Intercellular junctions

1- occluding junction
2- zonula adherens
3- macula adherens
  (desmosome)
4- gap junction
5- hemidesmosome
      Tight (occluding) junctions
• close apposition of the adjacent cell membranes.

• The cell membrane structural proteins of adjacent
  cells are fused together.

• The fusion may be band-like or spot-like

• no intercellular space between opposing
  membranes at the site of junction. (fused
  membranes)

•   It is found mainly between the simple columnar
    absorptive epithelial cells lining the intestine

• Function: It seals cells together and prevent
  diffusion of molecules in the intercellular space
  between adjacent cells
Tight (occluding) junctions
        Anchoring junctions
• Zonula adherens
band-like = zonula




• Macula adherens
  (Desmosomes)
 Spot = macula
                Zonula adherens
- It is a band-like specialization of the membrane and subjacent
   cytoplasm.

- In this junction, the intercellular space between opposing membranes
   is 20 nm.


- Structure: actin filaments of adjacent cells are linked together
    by protein    linkers and calcium.

- It is found mainly between the absorptive epithelial cells lining the
    intestine.

-   Function: It attaches strongly the cells together but without
    fusion.
          Zonula adherens


1- Actin filaments

2- Linkers

3- Calcium ions
                    Desmosomes
 - It is a spot-like specialization of the membrane and subjacent
    cytoplasm.

 - In this junction, the intercellular space between opposing
    membranes is 30 nm.

- It is found mainly between the stratified squamous epithelium of
   the skin.


- Structure: Intracellular intermediate filaments , attachment
  plaques and transmembrane proteins on both sides of adjacent
  membranes bind by filamentous material and calcium ions in
  the intercellular space.

 - Function: It provides a strong attachment between adjacent
   cells.
              Desmosomes
1- Attachment
plaques

2- Intermediate
filaments

3- Vertical
filamentous
 material
                      Filamentous material

4- Calcium
              Desmosomes

• attachment plaques



• intermediate filaments



• filamentous material
             Hemidesmosomes
- Structure:Half of a
desmosome.

-Spot-like

-It is found mainly
between the basal
cells and basal lamina
in stratified
squamous epithelium
of the skin.

- Found usually at the
base of the cell to
bind it to the basal
lamina.
Hemidesmosomes
       Anchoring junctions
• Zonula adherens




• Macula adherens
  (desmosomes)
            Gap junctions
• spot-like junction.

• narrow intercellular space (3nm).

• formed of connexons.

• found mainly in cardiac and smooth muscle
  cells.

• Function: It permits the exchange of
  molecules allowing integration,
  communication, coordination between
  epithelial cells.
 Connexons:

- six transmembrane
  proteins

- two connexons of
   opposing membranes are
   in register to form a
   channel connecting the
   cytoplasm of adjacent
   cells
           Gap junctions
                           connexons
• Cell membrane


• Communicating
  channel


• Intercellular space

								
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