Summarize the following text to main points and sub-points and make detailed explain for them:

 always arise during development (fetal life) from 
covering epithelium by means of cell proliferation and invasion of subjacent 
connective tissue followed by further differentiation: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Classification of Glandular epithelium: 
• 1- Glands are classified according to the presence or absence of  duct 
system into: 
1. Exocrine glands  
• secrete their products through the ducts that are connected to a surface.   
2. Endocrine glands  
• lack a duct system. They secrete their products into the bloodstream to 
reach their target cells. The products of endocrine glands are called 
hormones. 
3. Paracrine Glands   
• These glands are similar to endocrine glands, but their secretions reach 
target cells by diffusion through the extracellular space or immediately 
subjacent connective tissue.  
4. •Mixed glands  
• which have exocrine and endocrine functions as  pancreas.  
 
• 2- Glands are classified according to Number of secretory cells 
1-Unicellular glands  : consist of isolated glandular cells 
• Goblet cells are the only example of   unicellular glands. (a mucus-secreting 
cell positioned among other columnar cells) 
2-.Multicellular glands ( composed of clusters of cells ) 
• They form most of the glands of the body  
           e. g : salivary glands  
 
    
 
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• 3- Glands are classified According to Nature of secretion into:   
I-Mucus glands   
• Have a wide lumen acini.  
• Pyramidal cells.  
• Pale cytoplasm (foamy appearance)  
• periphery flattened dense nuclei.   
• Found in Sublingual glands. 
 II- Serous glands: -  
• Have narrow lumen  
• Pyramidal shape cells.  
• Multiple rounded basal  nuclei.  
• Apical cytoplasm is acidophilic (pink)  
• Basal cytoplasm is basophilic(purple)  
• e.g. parotid gland.   
III- Mixed glands Mixed acinus:   
-Mucus and serous secretion.  
Example: Submandibular gland.  
IV- Fatty secretory glands  as sebaceous glands.   
V- Watery secretory glands as sweat glands.  
 
• 4- Classification according to Mechanism of secretion:  
Merocrine glands: These glands do not show 
any cellular changes in their secretory cells (secretion 
by exocytosis) as in salivary glands. 
-Apocrine glands: (the apical parts of  the 
secretory cells of the glands are lost and come out with 
the secretion) . e.g. mammary glands.   
 
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-Holocrine glands: the whole cell is secreted (the whole 
secretory cells are destroyed and come out with the secretion). 
e.g. sebaceous glands    
 
5-Can be classified according to the arrangement of the secretory    
       cells and the branching of the duct  
Ducts:  
• If the duct is unbranched, the gland is called simple; 
I) Simple glands:   
a) 
 Simple tubular glands:  
▪ The secretory portion is tubular shape , 
▪ Single duct , single secretory portion. e, g  colon. 
  b-Simple coiled tubular gland 
▪ Tubular , coiled secretory portion. e.g. sweet gland 
 
 
c)Simple acinar glands :  
• Secretory portion is pocket like (flask shaped). As in penile 
urethra 
 
 
 
 
 
 
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II) –Simple branched glands :  
• These glands have several secretory units empty into an 
unbranched excretory duct. 
    a)Simple tubular branched glands.: Stomach (pyloric glands) 
    b) Simple branched aciner gland  -as in  (sebaceous glands)  
 
III- Compound glands :  
If the duct is branched, it is called  compound.    
Secretary portion:  
✓ If the secretory portion is shaped like a tube, the gland is 
compound tubular; As in Duodenum (Brunner’s glands).  
 
 
✓ If it is shaped like a flask, the gland is alveolar or acinar. As in 
mammary glands 
 
  
 
 
✓ the gland is tubuloalveolar if the secretary portion is a 
combination of the tube ends with a sac-like dilatation . e.g.  
submandibular and salivary glands.   
 
 
 
 
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III-Special epithelium 
 
1- Neuroepithelium:  
• The epithelial cells are modified to receive sensory stimuli.  
• In the taste buds in the tongue, retina in the eye and olfactory mucosa 
in    the nose. 
 
  2.Myoepithelial cells:  
• The  myoepithelial cells is to contract around the secretory or conducting 
portion of the gland and thus to help propel secretory products toward the 
exterior. 
• In the mammary, sweat, lachrymal and salivary glands. 
 
    3.Germinal epithelium:  
• It is a specialized epithelium for reproduction. 
• In the testis forming spermatozoa. 
• In the ovary forming ovum 
 
 
 
 
 
 
 
 
 
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Specialization of the cell surface 
1)Specializations of apical surface. 
 2) Specializations of basal  surface. 
   3) Specializations of lateral   surface 
 
 
1. Specializations of the apical Cell Surface 
• The free or apical surface of many types of epithelial cells contain 
specialized structures that increase the cell surface area or move 
substances & particles stuck to the epithelium   
1-Microvilli 
• Fingerlike cytoplasmic projections on the apical surface 
• few or numerous closely packed giving the appearance of brush border   
• Increase the surface of absorption (small intestine) 
 
 
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2-Stereocilia 
• long, branched , immotile microvilli   
• In sense organs (hair cells) serve as mechanoreceptors  
• In male reproductive system (epididymis) have 
absorptive function 
 
 
 
 
3-Cilia 
• Motile structures.  
• They are longer than the microvilli. 
•   Can be seen by light microscope.  
• Found in respiratory tract.   
 
 
 
4.Flagella:  
• They are present in the human body only in 
spermatozoa.   
• They are similar in structure to cilia but are much longer  
and are limited to one flagellum per cell.  
• For movement.   
 
 
 
 
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2- specialization of the Basal cell surface   
1-Basal lamina (EM):  
• A sheet-like extracellular structure celled basal 
lamina seen as a dens layer by E.M , It consists 
of:  
lamina lucida - electron lucent  
lamina densa - electron dense. 
• Basal lamina is composed of: collagen type IV, 
glycoprotein (laminin) and   proteoglycan.  
• Basal lamina is attached to the under lying 
connective tissue by fibers of collagen type VII 
and bundles of microfibrils. 
• Reticular lamina  - can be associated with reticular fibers  of the   
                                      underlying connective tissue 
2-Basement membrane (LM)   
• Non-cellular layer that joins an epithelium to underlying tissue 
• It is a periodic acid–Schiff (PAS)-positive layer which is visible with light 
microscope  
• Thicker than the basal lamina  
• Formed by fusion of the  basal lamina and  the reticular lamina  
   
 
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3- specialization of the Lateral cell surface   
• Classified according to the function and junctions between cells: 
1)  Impermeable junction: Zonulae occludens 
(tight junction) 
 
2)  Adhering junction: Zonulae adherens  
Desmosomes and Hemidesmosomes . 
 
 
3) Communication junction: Gap junction 
 
 
1.Tight junctions: 
• Most apical junction.  
• Form band that completely encircle the cell, 
closes off the intercellular space                         
completely.  
• With TEM, the two outer leaflets of membranes 
of neighbor cells are seen to fuse completely and 
the intercellular space between them is absent.  
• It form tight seal , surround cells, waterproof 
,Isolates wastes in the lumen.  
• The function: form a seal  that prevents the 
flow of material between epithelial cells.  
• e.g., in kidney : Columnar epithelium cells of 
kidney tubules and urinary bladder, The urine stays within kidney tubules.  
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2- Adhering junction                                                                                         
 a) Zonulae adherens  
• Located directly beneath  the occludens junction .   
• -With TEM, the insertion of numerous actin 
filaments   forming  electron-dense plaques of 
material on the  cytoplasmic surfaces of the 
junctional membranes 
• Function: Encircles the cell and provides for 
adhesion of one cell to its neighbor. 
 
 
 
b) Desmosome (macula adherns):  
• Disk shape structure.  
• The cell membranes are very strait in this region.  
• Located along the lateral membrane of most epithelial 
cells .  
• The adjacent cell membranes do not touch but held 
together intercellular                                             
protein filaments.  
• Site, Stratified squamouse epithelium of the skin, 
stomach, and urinary bladder.  
  
 
 
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c-Hemidesmosomes   
• In the contact zone between epithelial cells and 
the basal lamina.  
• These structures take the form of half 
desmosomes.   
• Function: Provide a basal adhesion   
 
 
 
3-Gap Junctions:  
• The two adjacent cells are communicated with each 
through narrow protein channels.  
• Through these channels; ions and nerve impulses pass 
from one cell to   another.  
• Commonly found in heart & some types of smooth muscle 
ensure synchronized contraction.  


Summary :