2. Learning Objectives
Introduction to saliva and its composition
Functions of saliva
Introduction to various types of salivary glands
Development of salivary glands
3. SALIVA
Complex fluid, produced by salivary glands .
Oral cavity kept moist by thin film of saliva which coats the
oral mucosa and the teeth
Saliva is over 99% water, yet the very small amount of
additional inorganic and organic compounds (such as
proteins, glycoproteins and enzymes) allows it to perform
many important functions.
Major role is related to the production of mucin, which acts
as a lubricant during mastication, swallowing and speech.
4. Composition of saliva
COMPOSITION OF SALIVA
Parameter Characteristics
Volume 600-1000 mL/day
Electrolytes Na⁺, K⁺, Cl¯, HCO¯3, Ca²⁺, Mg²⁺, HPO²¯₄,
SCN¯(thiocyanate), F¯
Secretory
proteins/peptides
Amylase, proline-rich proteins, mucins, histatin,
cystatin, peroxidase, lysozyme, lactoferrin,
defensins and cathelicidin-LL37
Immunoglobulins Secretory Ig A; IgG and IgM
Small organic Glucose, Amino acids, urea, uric acid and
lipid molecules
Other components Epidermal growth factor, insulin, cyclic
adenosine monophosphate-binding proteins,
serum albumin
5. Flow rate
Flow rate
(ml/min)
Whole Parotid Submandibular
Resting 0.2-0.4 0.04 0.1
Stimulated 2.0-5.0 1.0-2.0 0.8
pH 6.7-7.4 6.0-7.8
Mixed, or whole saliva:
It is the Oral fluid, which includes the secretions of the major glands, the
minor glands, desquamated oral epithelial cells, microorganisms and
their products, food debris, and serum components and inflammatory
cells that gain access through the gingival crevice.
6. Functions of Saliva
Protection:
Clearance: flushing away of bacteria and debris due to fluid nature of
saliva
Lubrication: mucins and other glycoproteins, allow smooth gliding
movements
Thermal/chemical insulation: saliva mucins protects mucosa from
chemical and thermal insults by reducing the concentration and lowering
temperature respectively
Pellicle formation: Proteins, glycoproteins, mucins bind to the surfaces of
the teeth and oral mucosa, forming a thin film, the salivary pellicle.
Help bind calcium to the tooth – protection
Also bind oral bacteria to the tooth, forming plaque
Buffering:
pH maintenance
Neutralization of acids
Bicarbonate, phosphate and basic proteins- neutralize the
acids produced by Metabolism of sugar by bacterias-
urea, ammonia: Also produced by bacteria through
metabolism of salivary proteins- helps neutralize the pH
7. Functions of Saliva
Antimicrobial activity:
Physical barrier- mucins
Acts as a barrier.
Also help to aggregate microorganisms, thus preventing their
adherence to oral tissues
Immune defense: immunoglobulin A(IgA),
also causes agglutination of specific microorganisms, preventing their
adherence to oral tissues and forming clumps that are swallowed
Nonimmune defense: Saliva also contains proteins with antimicrobial,
antiviral and antifungal activity
Peroxidase, lysozyme, lactoferrin, histatin, mucins, agglutinins, secretory
leukocyte protease inhibitor, defensins, and cathelicidin-LL 37
8. Functions of Saliva
Tooth integrity:
Saliva helps in Enamel maturation and repair: through high levels
of Calcium, phosphate & fluoride, along with calcium binding
proteins like statherin, acidic proline-rich proteins
Tissue repair:
a variety of Growth factors & trefoil proteins are present in small
amounts in saliva– help in tissue growth, differentiation and
wound healing.
Digestion:
Bolus formation: water & mucins help to lubricate the food and
help in bolus formation and swallowing
Starch, triglyceride digestion: is facilitated by enzymes like
Amylase & lipase in saliva
9. Functions of Saliva
Taste:
Solubilization of molecules:
Water & lipocalins in saliva help to dissolve the food substances,
so that they can be sensed by taste buds
Saliva produced by minor glands in the vicinity of the
circumvallate papillae (Von Ebner Glands) contains proteins that
are believed to bind taste substances and present them to the
taste receptors.
Maintenance of taste buds: Epidermal growth factor and
carbonic anhydrase VI
Speech:
Saliva helps to keep the oral cavity moist, which facilitates
speech and deglutition.
10.
11. SALIVARY GLANDS
Salivary glands are a group of Compound tubuloacinar exocrine
glands found in the oral cavity that secrete complex fluid known as
saliva.
Merocrine glands- secrete products from intact cells through
exocytosis.
12. Important points to remember
The salivary glands are compound glands as they have
more than one tubule entering the main duct.
A duct is a passage that allows the glandular secretion
emptied directly into an anatomic location where the
secretion is to be used.
The salivary glands have numerous ducts associated with
them hence they are exocrine glands
The architectural arrangement of the salivary glands is
tubuloacinar, where acini are secretory units (which is the
basic functional unit of a salivary gland).
These tubuloacinar units are merocrine as they release only
the secretion of the cell from the secreting units.
14. Classification of Glands
(according to location)
Major and minor salivary glands.
Three pairs of major salivary glands—
Parotid gland
Submandibular gland,
Sublingual gland
They are located outside the oral cavity, with extended duct
systems through which the gland secretions reach the mouth.
15. Classification of Glands
(according to location)
Numerous smaller minor salivary glands:
Located in various parts of the oral cavity, typically located
in the submucosal layer, with short ducts opening directly
onto the mucosal surface
The labial, lingual, palatal, buccal, glossopalatine, and
retromolar glands.
Anterior lingual glands (glands of Blandin and Nuhn)- near the
apex of the tongue and ventral surface of tongue
Glands of Von Ebner- locate on posterior aspect of tongue
below the sulci of circumvallate and foliate papillae
16. Anatomy of Salivary glands
Parotid gland:
Largest salivary gland.
Weighs between 14 and 28 g.
Pyramidal in shape
Superficial portion of the
parotid gland is located
subcutaneously, in front of the
external ear, and its deeper
portion lies behind the ramus
of the mandible.
Closely associated with facial
nerve
17. Parotid Gland
The duct (Stensen’s duct):
runs forward across the masseter
muscle, turns inward at the
anterior border of the masseter,
and opens into the oral cavity at
a papilla opposite the maxillary
second molar.
Small amount of parotid tissue
occasionally forms an accessory
gland associated with Stensen’s
duct, just anterior to the
superficial portion.
18. Parotid Gland
Vascular supply and lymphatic drainage:
Arterial supply: From branches of the external carotid artery as
they pass through the gland.
Venous drainage: External jugular vein
Lymphatic drainage: Upper deep cervical lymph nodes
Nerve supply:
Sensory supply: Greater auricular nerve and Auriculotemporal
nerve
Parasympathetic nerve supply: Mainly from the glossopharyngeal
nerve (cranial nerve IX). The preganglionic fibers synapse in the
otic ganglion; the postganglionic fibers reach the gland through
the auriculotemporal nerve.
Sympathetic innervation of all of the salivary glands is provided by
postganglionic fibers from the superior cervical ganglion, travelling
with the blood supply.
19. Submandibular gland
Second largest gland
Also called “Submaxillary gland”
10 – 15 gm (half the weight of
parotid)
Located at posterior portion of
the floor of the mouth, medial
aspect of mandible and
wrapping around posterior
border of mylohyoid
20. Submandibular gland
The excretory duct
(Wharton’s duct)
runs forward above the
mylohyoid muscle and
opens into the mouth
beneath the tongue at
the sublingual
caruncle, lateral to the
lingual frenum.
21. Submandibular gland
Blood supply: From the lingual and facial arteries.
Lymphatic drainage: The lymphatic drainage is to the deep
cervical and jugular chain of nodes
Nerve supply:
Parasympathetic innervation is derived primarily from the VII
cranial nerve (facial nerve) reaching the gland through the
lingual nerve after synapsing in the submandibular ganglion.
Sympathetic innervation: postganglionic fibers from the
superior cervical ganglion, travelling with the blood supply.
22. Sublingual gland
Smallest major salivary gland.
2 g weight
Located in the anterior part of
the floor of the mouth between
the mucosa and the mylohyoid
muscle.
Secretions of the sublingual
gland enter the oral cavity
through
series of small ducts (ducts of
Rivinus) opening along the
sublingual fold
often through a larger duct
(Bartholin’s duct) that opens with
the submandibular duct at the
sublingual caruncle.
23. Sublingual Gland
Blood supply: Sublingual and submental arteries.
Lymphatic drainage: Submandibular and submental lymph
nodes
Nerve supply:
Parasympathetic supply: The facial nerve (cranial nerve VII)
provides the parasympathetic innervation of the sublingual
gland, via the lingual nerve and submandibular ganglion.
Sympathetic innervation: postganglionic fibers from the superior
cervical ganglion, travelling with the blood supply.
24. Minor salivary glands:
There are 600 to 1000 minor salivary glands lying beneath the
oral epithelium
Exists as aggregates of secretory tissue present in submucosa
throughout most of the oral cavity and oropharynx.
Not seen in gingiva and anterior part of hard palate.
25. Minor salivary glands
They are predominantly mucous glands, except for Von-
Ebner gland, which are serous.
Rich in mucin, antibacterial proteins and secretory
immunoglobulins.
Continuous slow secreting glands, thus have an important
role in protecting and moistening oral mucosa, especially
when major salivary glands are mostly inactive (especially
during sleep).
Located in various parts of the oral cavity—the labial, lingual,
palatal, buccal, glossopalatine, and retromolar glands.
Typically located in the submucosal layer, with short ducts
opening directly onto the mucosal surface.
26. Von Ebner’s glands (lingual serous glands)
They are the only serous minor
salivary glands (the rest of minor
glands are mucous)
Located in the tongue, opening
into the troughs surrounding:
circumvallate papillae on the
dorsum of the tongue
foliate papillae on the side of the
tongue.
Secrete digestive enzymes
(salivary lipase) and proteins =
play a role in taste process
Fluid of their secretion cleanse the
trough and prepare the taste
receptors for new stimulus
27. DEVELOPMENT OF SALIVARY
GLANDS
Develop from the “ectoderm”
Initiation of development:
Parotid gland: 4 to 6 weeks
Submandibular glands: 6 weeks
Sublingual and minor salivary glands: 8 to 12 weeks
Cells of secretory end pieces attain maturity during the last 2
months of gestation.
28. Development of salivary glands
Bud formation
Formation and growth of
epithelial cord
Branching
morphogenesis
Canalization
Cytodifferentiation
29.
30. Stage 1 (bud formation)
Develops as proliferation of oral epithelium into the
underlying ectomesenchyme (condensing around the
bud)
A thin basal lamina separates the bud from underlying
mesenchyme.
The specific mesenchyme associated with the salivary
glands provides optimum environment for gland
formation.
31. Stage 2 (Formation and growth of
epithelial cord)
As the bud continues to
proliferate into underlying
mesenchyme, it is
connected to the surface
by a trailing cord of
epithelial cells (arrow head).
Mesenchymes (MES)
condenses around the bud.
32. Stage 3 (Branching Morphogenesis)
Initiation and branching in
terminal/ distal parts of epithelial
chord (arrow heads )
Clefts develop in the bud,
forming two or more buds
Resulting in branching
morphogenesis which produces
successive generations of buds
and hierarchic ramification of
glands
33. Hypothesis of branching morphogenesis:
Epithelial mesenchymal interactions
Fibroblastic growth factor family, sonic hedgehog,
Transforming growth factor-β,and their receptors.
Differential contraction of actin filaments at the basal
and apical ends of the epithelial cells
Provide physical mechanism underlying cleft
formation.
Deposition of ECM components within the clefts
serves to stabilize them
34. Stage 4 (Canalization)
Lumen formation takes place
at the distal end of the cord,
then proximal and finally in the
central portion of main cord
Lumina form within the ducts
before they develop within the
terminal buds. (arrows)
May involve apoptosis of
centrally located cells in the
cell cords
35. Stage 5 (Cytodifferentiation)
Following development of lumen in the terminal buds, the
epithelium consists of two layers of cells
Cells of the inner layer --- mucous or serous cells depending upon
the specific glands
Cells of the outer layer --- contractile myoepithelial cells present
around secretory end pieces and intercalated ducts.
36. As the epithelial parenchymal
cells increase in size and number,
the associated mesenchyme
(C.T) is diminished --- thin layer
remains surrounding each duct
and secretory end piece of the
gland.
Thicker C.T. (septa) divide the
gland into lobes and lobules
40. Secretory end pieces
The basic functional unit of the salivary gland is the terminal
secretory piece called Acini.
Spherical secretory end pieces and tubular secretory end pieces
(acini)
The acini/ secretory end piece is made up of
Serous cells
Mucous cells
Myoepithelial cells
41. SEROUS CELLS Pyramidal cells located in serous end
pieces
Apical cytoplasm contain electron
dense granules called zymogen
granules
Spherical nuclei basally
Basal cytoplasm:
Packed with increased RER, located
basal and lateral to nuclei
Small golgi apparatus (4-6 saccules)
lateral and apical to the nuclei
Thus it is a typical protein secreting cell
Produce proteins and glycoproteins,
which have well defined enzymatic,
antimicrobial, calcium-binding activities
Serous glycoproteins have N-linked
oligosaccharides side chains
42. SEROUS CELLS
Plasma membrane:
Luminal as well as intercellular
canaliculi studded with few
short microvilli
Lateral surface occasional
folds
Basal surface is thrown into
regular folds, 0.5µm deep.
Increases surface area.
Intercellular canaliculi:
finger like extension of the
lumen between adjacent
cells,
increase the size of luminal
surface (arrow heads)
44. Mucous cells
Pyramidal shape
Apical cytoplasm contains mucus
which compress the nucleus and
RER towards the base.
Large golgi complex
10- 12 saccule stacked above the
nucleus
ER limited to basal cytoplasm
Thus.. It has little or no enzymatic
activity
Secrete mucins, which are
glycoproteins.
Have O-linked oligosaccharide side
chain.
45. Mucous cells
Unstained by H&E stain.
Periodic acid–Schiff (PAS) and
Alician blue stains positive.
Glycoproteins in Mucous cells
stain strongly with PAS and
Alician blue- dark purple
Glycoproteins in Serous
demilunes (arrow heads) stain
only with PAS -magenta
46. Mucous cells
Same intercellular junctions as serous cells
Mucous acini lack intercellular canaliculi except for those
covered by serous demilunes/ cresent shaped cells.
Secretions from these demilunes reach the lumen through
intercellular canaliculi.
Main function is to lubricate and form a barrier on surfaces
47.
48. Serous Secretory end pieces: Mucous secretory end pieces
• Spherical shape • Tubular shape
• Composed of 8- 12 cells
surrounding a central lumen
• Fewer cells
• Central lumen is larger
• Serous acini stain dark • Mucous acini stain light
• No demilunes on serous acini • Serous cells may be present
as Demilune on mucous
acini
• Secrete serous, watery saliva
• Proteinaceous secretion
• Secrete thick viscous saliva
• Mucopolysaccharides
49. DUCTS
A duct is a passage that allows the
glandular secretion emptied directly into
an anatomic location where the secretion
is to be used.
1. Intralobular ducts:
Intercalated ducts
Striated ducts
2. Interlobular ducts
Excretory duct
50.
51. INTERCALATED
DUCTS
Intralobular duct
Primary saliva produced by
secretory end pieces passes 1st
through this duct.
Lined by simple cuboidal
epithelium
Myoepithelial cells located
along the basal surface
Diameter smaller than the end
pieces but lumina is larger.
Join to form larger intercalated
ducts before emptying into
straited ducts
52. INTERCALATED DUCTS
Cuboidal cells
Central nuclei
Few small secretory granules
Few RER
Small golgi complexes
Few short microvilli
Junctional complexes-
scattered desmosomes and
gap junctions
Lateral foldings
53. INTERCALATED DUCTS
Functions:
Contribute macromolecular components like
lysozymes and lactoferrins.
A portion of the fluid component of primary saliva is
added by this ductal region.
Undifferentiated cells (stem cells of salivary glands)
– undergo proliferation and differentiation to
replace damaged or dying cells in the end pieces
and striated ducts
54. STRIATED DUCTS
Intralobular duct i.e. Main
ductal component located
within the lobules
Receive primary saliva from
intercalated ducts
Diameter of the duct is greater
than secretory end pieces.
Lumen also larger
55. STRIATED DUCTS
Tall Columnar cells
Central nuclei
Pale acidophilic/eosinophilic
cytoplasm
Radially oriented striations observed in
the basal cytoplasm.
Abundant large mitochondria present
between these infoldings
Indicating that the cell is involved in
active transport
Basal lamina encloses the duct,
capillary plexus is present in C.T.
lack gap junctions
56. STRIATED DUCTS
Functions:
Modification of primary saliva by
reabsorption of Na⁺ and secretion of
HCOᶾ¯ and K⁺.
Presence of vesicles suggest that these cells
participate in endocytosis of substances from
the lumen
57. EXCRETORY DUCTS
As the striated ducts leave the
individual glandular lobules
and enter the interlobular C.T.
they join to form excretory
ducts
Larger in diameter than straited
ducts
Main excretory duct leading
from gland to the oral cavity.
58. ED seen to be located in C.T septa in between the lobules i.e
interlobular
Larger in diameter than straited ducts (arrow heads)
59. In smaller ducts i.e. near the
striated ducts: lined by
pseudostratified epithelium.
Columnar cells extending towards
the lumen
Basal cells do not reach the lumen
Numerous capillaries and venules
present around the duct
In larger excretory ducts, basal
cells increase in no. and mucous
goblet cells also present
60. EXCRETORY DUCTS
Epithelium becomes stratified near the oral opening.
In smaller ducts, columnar cells are similar to striated
duct cells
As ducts increase in size, no. of mitochondria and
infoldings on basolateral surface decrease.
Basal cells have numerous bundles of intermediate
and actin filaments and numerous processes similar
to myoepithelial cells
61. EXCRETORY DUCTS
Cells associated with excretory ducts:
1. Tuft (caveolated or brush) cells
Receptors like cells with long stiff microvilli and apical vesicles
Nerve endings are associated with basal portion of these cells
2. Cells :
macrophages,
lymphocytes
dendritic cells/ antigen presenting cells –
Function of excretory duct:
Modification of final saliva by altering its electrolyte
concentration
62. Myoepithelial cells
Stellate or spider like cells– also termed as basket cells
Contractile cells associated with
Secretory end pieces – stellate shaped with numerous branching processes–
embrace the end pieces
Intercalated ducts – fusiform shaped with less processes, oriented lengthwise along
the duct
Joined to the cells by desmosomes
Processes filled with actin and myosin – thus resemble smooth muscles BUT
derived from epithelium.
Located on epithelial
side of basal lamina
63.
64. Functions of myoepithelial cells
Provide support to the end pieces during active salivary
secretion
Help to expel primary saliva from end piece into duct
system
Provide signals to acinar secretory cells necessary for cell
polarity and structural organization of secretory end pieces
Produce proteins with tumor suppressor activity like
Proteinase inhibitors
Antiangiogenesis factors
