Histology of Salivary Glands
What is a gland?
Gland is an organ of secretion
made up of specialized
secretory cells derived from
the surface epithelium on
which it opens.
General Features
• Epithelial in origin
• Present as discrete organs or in
layers.
• Secretory cells form functional
units called secretory end piecesmay be flask (Acinus)or cylindrical
(Tubular)shaped
Types of Secretory units
General Features
• Fluid secreted may be enzymes, hormones or
mucus.
• Secretion is modulated by nervous and
hormonal influences.
• Myoepithelial cells- star shaped, contractile,
lie between the secretory cells and the
basement membrane
Mixed Salivary Gland
Development
• Develop as invagination of the epithelium
into the underlying vascular connective tissue.
• Distal part forms glandular or Secretory end
Piece – functionally an active portion.
• Proximal part-Excretory Duct-opens on the
surface of the epithelium
• Some cells get detached from the epithelial
surface- Ductless or endocrine glands
Development of Gland
Glandular Epithelium
Classification of Glands
Based on the site of Secretion
• Exocrine Gland
• Endocrine Gland
• Paracrine Gland- secretes its products into
the local extracellular space affecting the
surrounding cells e.g. enteroendocrine cells
of gastrointestinal tract (GIT)
Classification of Glands
• Based on the Number of cells
• Unicellular Gland- goblet cells in the
respiratory and intestinal tracts
• Multicellular Gland- all glands other than
goblet cells
Classification of Glands
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Based on the Number of Ducts and the shape
of secretory end piece
Simple Gland- one duct
Compound Gland- has minor and major ducts
Both the types are further subdivided into
Tubulo, Alveolar/Acinar or
Tubulo-alveolar/acinous
Multicellular Glands
Compound Tubulo-alveolar
Compound Tubulo-alveolar
Compound Glands
• Simple Alveolar-Penile urethra
• Simple Branched alveolar-Sebaceous gland
• Compound Alveolar- Pancreas, Parotid, Mammary
gland and glands of Respiratory tract.
• Simple Tubular-Crypts of Leiberkuhn
• Simple branched tubular-Uterine glands,Pyloric and
fundic glands
• Compound Tubular-Brunner’s Gland, Cardiac glands
• Simple coiled tubular-Sweat gland
• Compound Tubulo-alveolar- Submandibular &
Sublingual salivary glands
Mixed Salivary Gland
Classification of Glands
Based on the Mode of Secretion
• Merocrine Gland- No loss of Cytoplasm-e.g.
most of the compound glands e.g. Pancreas
Also known as Eccrine or Epicrine
• Apocrine Gland- Partial loss of cytoplasm-e.g.
lactating mammary gland, sweat glands in the
axilla and external genitalia
• Holocrine Gland- Complete loss of cytoplasm
e.g. sebaceous and tarsal gland
• Cytocrine Gland- Cells are released as secretion.
e.g. Testis (spermatozoa)
Modes of Secretion
Classification of Glands
Based on the Nature of Secretion
• Serous Gland- thin, watery secretion rich in
enzymes e.g. Parotid gland
• Mucous Gland- thick, viscous secretion for
protection and lubrication. e.g. Sublingual
salivary gland
• Mixed Gland (seromucous)- both watery and
viscous material.e.g. Submandibular salivary
gland
Difference between Serous & Mucous
Acini
Serous
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Thin, watery
Proteinaceous secretion
Zymogen granules in cyto
Central rounded Nucleus
Small Lumen
Indistinct cell bondaries
Darkly stained
Enzymatic action
Parotid Gland
Mucous
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Thick, viscous
Mucopolysaccharides
Mucigen droplets
Nucleus-flat & peripheral
Large Lumen
Distinct cell boundaries
Lighly stained
Protection & lubrication
Sublingual gland
Mixed salivary gland
• Serous Acini
• Mucous Acini
• Seromucous Acini- having Serous demilunes
General Architecture of a Compound
Gland
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Gland may be divided into lobes and lobules.
ParenchymaSecretory end pieces- Acini/tubules /tubuloacinar)
Ducts- Intralobular, interlobular, main excretory
duct
Stroma
Capsule
Septa (interlobular, interlobar)
Loose intralobular connective tissue supporting
the parenchyma
Clinical
• ADENOMA: Benign tumors arising in the
gland
• ADENOCARCINOMA: Malignant growth in the
gland
Parotid Gland
Parotid Gland
Intra-glandular adipose tissue in
parotid gland
Submandibular Gland
Submandibular Gland
Mixed Salivary Gland
Mucous Acini
Sublingual-purely mucous gland
Sublingual
Minor salivary glands of Palate
• Aggregations of Mucous
acini
• No striated duct
Minor salivary glands of Palate(High
Power)
• Mucous acini with
central Lumen
• Large Pyramidal cells
with granular cytoplasm
• Nucleus towards the
basement membrane
The minor salivary glands are small aggregates of unencapsulated mucous
or serous glands. In the tongue they are in intimate contact with the
striated muscle tissue.
Keratin cocktail stains intercalated, striated and interlobular ducts, but
acinar and myoepithelial cells are mostly negative.
MCQ
• The serous gland can be identified by the
presence of serous acinus with
• A) Small Lumen
• B)Large Lumen
• C)Flat peripheral Nuclei
• D)Mucigen droplets
MCQ
• When there is a complete loss of cytoplasm
resulting in cell death of the secretory cell
during the process of secretion, the gland is
said to be
• A) Merocrine
• B) Apocrine
• C) Holocrine
• D) Cytocrine
MCQ
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Sebaceous gland is an example of
Holocrine gland
Apocrine gland
Merocrine gland
Unicellular gland
MCQ
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Mucous Acinus
A) Secretes thin watery fluid
B) Has flat, peripheral nucleus
C) Has a small lumen
D) Contains zymogen granules
MCQ
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Sweat glands in the axilla are an example of
A) Merocrine gland
B) Apocrine gland
C) Holocrine gland
D) Cytocrine gland