Salivary glands and saliva

By- Dr. Praveen kumar singh
PG

Contents
 Introduction
 Anatomy
 Development
 Histology
 Physiology
 Functions of saliva
 Applied Phsiology

INTRODUCTION
 The oral cavity is a moist environment, a film of
fluid called saliva constantly coats its inner
surfaces and occupies the space between the
lining oral mucosa and the teeth.
Saliva is a complex fluid, produced by the
salivary glands, whose important role is
maintaining the wellbeing of the mouth.
Patients with a deficiency of salivary secretion
experience difficulty eating, speaking,
swallowing as well as become prone to mucosal
infections and rampant caries.

ANATOMY
 There are three pairs of major salivary
glands.
1. Parotid glands
2. Submandibular glands
3. Sublingual glands.
 There are more than 400 minor salivary
glands (labial, lingual, palatal, buccal,
glossopalatine and retromolar).

Parotid gland
FEATURES=>
 Para-around ; otic-ear
 It is the largest salivary gland
 It wieghs about 15 gm
 Situated below the external acoustic meatus,
between the ramus of the mandible and
sternocliedomastoid.
 A part of this forward extension deattched and
known as accessory parotid and it lies between
the zygomatic arch and the parotid duct.

Capsule of the parotid gland
 Investing layer of the deep cervical fascia
forms capsule for the gland.
 Fascia splits to enclose the gland.
 The superficial lamina is thick and adherent
to the gland and attached above to the
zygomatic arch.
 The deep lamina is thin and is attached to
the styloid process, the angle and the
posterior border of the ramus of the
mandible and the tympanic plate.

 A portion of deep lamina extending between
the styloid process and the mandible is
thickened to form the stylomandibular
ligamnet which separates the parotid gland
from the submandibular salivary gland.
 The ligament is pierced by the external
carotid artery.

External features
 The gland resembles three sided pyramid.
 Apex of pyramid is directed downwards .
 The gland has four surfaces:-
 Superior(base of pyramid)
 Superficial
 Anteriomedial
 posteromedial

 The surfaces are separated by three
borders:
 Anterior
 Posterior
 Medial/pharyngeal

Structures within the gland
a. Arteries b. Veins

c. Facial nerve
Pattern of branching is called pes anserinus
Patey’s
faciovenousplane

Parotid duct/ stenson’s duct
 It is thick walled and about 5 cm long.
 It emerges from the middle of the anterior
border of the gland.
 It runs forward and slightly downwards on
the masseter.

Stenson’s duct relations are:-
Superiorly:-
 Accesory parotid gland
 Transverse facial vessels
 Upper buccal branch of the facial nerve
Inferiorly
 Buccal fat pad
 Buccopharyngeal fascia
 Buccinator (obliuquely)

Blood supply:
Arterial:
o External carotid artery
o Its terminal branches
o Posterior auricular
o Superficial temporal
o Transverse facial arteries
Venous:
 Retromandibular vein

Lymph drainage:
Into parotid lymph nodes and deep
cervical lymph nodes.

Autonomic nerve innervation
1. Parasympathetic secretomotor fibers from the
inferior salivatory nucleus of the ninth cranial
nerve supply the parotid gland. The nerve fibers
pass to the otic ganglion via the tympanic branch of
the ninth cranial nerve and the lesser petrosal
nerve.
2. Postganglionic parasympathetic fibers reach the
parotid gland via the auriculotemporal nerve,
which lies in contact with the deep surface of the
gland.

 Post-ganglionic sympathetic fibers reach the
gland as a plexus of nerves around the
external carotid artery.

 Sympathetic nerves are vasomotor and are
derived from the plexus around the middle
meningeal artery.
 Sensory nerves to the gland come from the
auriculotemporal nerve, but the parotid
fascia is innervated by the great auricular
nerve (C2, C3).

Applied aspects
 Parotid swellings are very painful due to the
underlying nature of the parotid fascia.
 The lobule of the ear is often pushed up in
parotid swelling
 Mumps is infection of salivary gland caused
by paromyxovirus which will cause severe
pain

 A parotid abscess may be caused by the
spread of infection from the oral cavity.
 An infection may also spread due to the
parotid lymph node draining an infected
area.
 For tumours of the parotid gland incision
biopsy is not indicated as it will cause the
seeding of the tumour .

 Parotidectomy is the removal of the parotid
gland. After this operation at times there may
be regeneration of the secretomotor fibres in
the auriculotemporal nerve which join the
great auricular nerve.
 This causes stimulation of the sweat glands
and hyperaemia in the area of its distribution
thus producing redness and sweating in the
area of skin supplied by the nerve.

 This clinical entity is called FREY
SYNDROME.
 Whenever such a person chew there is increase
in the sweating in the region supplied by
auriculotemporal nerve.
 So it is called auriculotemporal syndrome

Submandibular salivary gland
 Second largest salivary
gland
 Situated in the anterior
part of the the
diagastric traingle
 Gland is size of walnut
 It is roughly J-shaped

Superficial part
 Inferior surfaces
 Lateral surface
 Medial surfaces
 The gland is enclosed to
between two layers of
deep cervical fascia.

Relations
Inferior surface is covered by:-
 Skin
 Platysma
 Cervical branch of the facial nerve
 Deep fascia
 Facial vein
 Submandibular lymph nodes

Lateral surface related to:-
 Submandibular fossa related to the mandible
 Insertion of the medial pterygoid
 Facial artery

Medial surface related
to the:-
 Mylohyoid
 Hyoglossus
 Styloglossus muscle
Inferiorly : it overlaps stylohyoid and the
posterior belly of the diagastric.

Deeper part
 Small in size
 Situated deep to the mylohyoid
line and superficial to the
hyoglossus and styloglossus
 Posteriorly, it is continuous with
the superficial part round the
posterior border of the
mylohyoid.
 Anteriorly, it extends up to the
posterior end of the sublingual
gland

Relations
 Present in between mylohyoid and
hyoglossus
 Laterally- Mylohyoid
 Medially- Hyoglossus
 Above – lingual nerve with sub mandibular
ganglion
 Below – Hypoglossal nerve

Relation to facial vein and
artery---

Submandibular duct / wharton’s
duct
 Thin walled and is about 5 cm long.
 Emerges from the anterior end of the deeper part
of the gland.
 Runs forward to the hyoglossus between the
lingual and hypoglossal nerves.
 At the anterior border of the hyoglossus, duct is
crossed by the lingual nerve.
 Opens in the floor of the mouth on the summit of
sublingual papilla, at the side of the frenulum of
the tongue.

BLOOD SUPPLY(ARTERIAL)
 Submental and sublingual arteries.
 Facial artery.
 Lingual artery.
BLOOD SUPPLY(VENOUS)
 Anterior facial vein.
 Common facial vein.
LYMPHATIC DRAINAGE
 Submandibular lymph nodes.

 Vasomotor sympathetis- fibres from the
plexus on the facial artery.
 Sensory fibres - Lingual nerve.

Applied aspects
 The formation of calculus is more common in
the submandibular gland than in the parotid.
 A stone in the submandibular duct(wharton’s
duct) can be palpated bimanually in the floor of
the mouth and can even be seen if sufficiently
large.

Sublingual salivary gland
 Smallest of the three salivary gland
 Almond shaped and weighs about 3 to 4
gm

 Lies above the mylohyoid below the mucosa of
the floor of the mouth, medial to sublingual fossa
of the mandible and lateral to the genioglossus.

Relations
 Front- meet with the opposite side gland
 Behind – comes in contact with the deeper
part of the submandibular gland
 Above- mucous membrane of the mouth
 Below- mylohyoid muscle
 Lateral- sublingual fossa
 Medial- genioglossus muscle

 Sublingual gland has no true fascial capsule.
 It lacks a single dominant duct. Instead, it is
drained by approximately 10 - 12 small ducts
(the Ducts of Rivinus).
 Ducts of Rivinius either secrete directly into
floor of mouth or empty into BARTHOLIN’s
duct that then continues into Wharton’s duct.
 The gland receives blood supply from the
lingual and submental arteries.
 Nerve supply is similar to that of
submandibular gland

Applied aspects
 The structures at risk during dissection of
the gland are the submandibular duct and the
lingual nerve.
 The duct lies superficially in the floor of the
mouth medial to the sublingual fold, and is
crossed inferiorly by the nerve which then
enters the tongue
 The sublingual artery and vein also lie on
the medial aspect of the gland close to the
submandibular duct and lingual nerve.

Minor salivary glands
 About 600 to 1,000 minor salivary glands,
ranging in size from 1 to 5 mm, line the oral
cavity and oropharynx.
 These lie just under mucosa.
 Distributed over lips, cheeks, palate, floor of
mouth & retro-molar area.
 Also appear in upper aero-digestive tract
 Contribute 10% of total salivary volume.

DEVELOPMENT of salivary glands

 The salivary glands develop as outgrowth of
the buccal epithelium.
 The outgrowths are at first solid and are later
canalised.
 They branch repeatedly to form the duct
system.
 The terminal parts of the duct system develop
into secretory acini.

 As the salivary glands develop near the
junctional area between the ectoderm of the
foregut, it is difficult to determine whether they
are ectodermal or endodermal.
 The outgrowth for the parotid gland arises in
relation to the line along which the maxillary
and mandibular process fuse to form the cheek.
it is generally cosidered as ectodermal.

 The outgrowths for the submandibular and
sublingual glands arise in relation to the linguo-
gingival sulcus. They are usually cosidered to
be of endodermal origin.

Structure of salivary glands
 The working parts of the
salivary glandular tissue consist
of the secretory end pieces
(acini) and the branched ductal
system.
 In serous glands (e.g. the
parotids) the cells in the end
piece are arranged in a roughly
spherical form.
 In mucous glands, they tend to
be arranged in a tubular
configuration with a larger
central lumen.

 In both types of gland the cells
in the end piece surround a
lumen and this is the start of
the ductal system.
 There are three types of duct
present in all salivary glands.
 Intercalated duct
 Striated duct
 Excretory duct

The fluid first passes through the
intercalated ducts which have low
cuboidal epithelium and a narrow
lumen.
From there the secretions enter the
striated ducts which are lined by
more columnar cells with many
mitochondria.
Finally, the saliva passes through the
excretory ducts where the cell type is
cuboidal until the terminal part which
is lined with stratified squamous
epithelium.

 End pieces may contain mucous cells, serous
cells or a mixture of both.
 A salivary gland can consist of a varied mixture
of these types of end pieces.
 In mixed glands, the mucous acini are capped by
a serous demilune.
 In addition, myoepithelial cells surround the end
piece, their function being to assist in propelling
the secretion into the ductal system.
 The gland and its specialised nerve and blood
supply are supported by a connective tissue
stroma.

Differences:-
Serous acini Mucous acini
1. Samller in size,rounded in
shape.
2. Lumen hardly visible.
3. Lining cells pyramidal in
shape and relatively more in
number.
4. Nuclie are round and basal.
5. Cytoplasm depicts basal
basophilia and apical
eosinophilia.
6. May present as demilunes on
one aspect of some mucous
acini
1. Larger in size , more variable
in shape.
2. Lumen mostly visible.
3. Lining cells truncated
columnar in shape. Cells
relatively fewer in number.
4. Nuclie are flattened and
peripheral.
5. Cytoplasm is pale and
vacuolated.
6. Mucous acini only present as
complete acini.

Physiology of saliva
Composition-
 Saliva is slightly cloud in appearance due to the
presence of cells and mucin.
 Saliva is slightly acidic and the Ph varies from
6.7 to 7.4, specific gravity is 1.002 to 1.012.
 The resting rate of saliva is on an average is
about 0.3 to 0.4 ml/min..
 Saliva contains about 99.5% of water and 0.5%
of solid.

Solid present in saliva consists:-
 Cellular costituents – consist of yeast, bacteria,
protozoa, polymorphonuclear leukocytes and
desquamated epithelial cells.
 Inorganic ions- major(Na + ,k+ ,Cl-,HCO3-) and
Minor (Ca++ ,Mg++ ,HPO4-, I, Scn- and F-)

 Secretory proteins and glycoprotiens – various
enzymes, large carbohydrte rich protien or
mucin, antibacterial substance, group of
protiens involved in enamel.
 Serum constituents- albumin, blood clotting
factor , B2 microglobulin and immunoglobulin.

Source of saliva-
 Saliva is secreted from the salivary glands: via
parotid gland-25%; submandibular gland –
70% ; sublingual gland – 5%
 Minor salivary gland present on palate , buccal
mucosa, and tongue also produce modest
amounts of saliva.

 Normal stimulated flow of saliva- for different
ages can be calculated by the equation:-
0.78 * age + 5.6 = stimulated flow / 15 min
5.6 – it is stimulated flow of the infants

Secretion of saliva
 Although fluid secretion occurs only through the
acini, proteins are produced and transported into
the saliva through both acinar and ductal cells.
 The primary saliva within the acinar end pieces
is isotonic with serum but undergoes extensive
resorption of sodium and chloride and secretion
of potassium within the duct system.
 The saliva, as it enters the oral cavity, is a
protein-rich hypotonic fluid.

 The secretion of saliva is controlled by
sympathetic and parasympathetic neural input.
 The stimulus for fluid secretion is primarily via
muscarinic-cholinergic receptors, whereas the
stimulus for protein release occurs largely
through b-adrenergic receptors. Salivary cells
also display an array of additional receptors that
influence secretory functions.

 Activation of these receptors induces a
complex signaling and signal transduction
pathway within the cells, involving numerous
transport systems, resulting in a tightly
regulated secretion process.
 Mobilization and regulation of intracellular
calcium are a critical component of this process
within the secretory cells.

Nervous Regulation of Salivary
Secretion
 The salivary glands are controlled mainly by
the parasympathetic nervous signals all the way
from the superior and inferior salivatory nuclei
in the brain stem.
 The salivatory nucleus located at the juncture
of the medulla and pons and are excited by
both taste and tactile stimuli from the tongue
and other areas of the mouth and pharynx.

 Sour taste stimuli elict the saliva secretion 8 to 20
times than the basal rate.
 Salivation can also be stimulated or inhibited by
nervous signals arriving in the salivatory nuclei
from higher centres of the central nervous
system.
 The appetite area of the brain , which partially
regulates secretion is located in proximity to the
parasympathetic centres of the hypothalmus, and
it function to great extent in response to signals
from the taste and smell area of cerebral cortex or
amygdala.

 Sympathetic stimulation can also increase the
salivation a slight amount, much less so than
does parasympathetic stimulation. The
sympathetic nerves originate from the superior
cervical ganglia and travel along the surfaces of
the blood vessels walls of the salivary glands.

Functions of saliva
Function Action
Fluid/Lubricant Coats hard and soft tissue which helps to protect against
mechanical, thermal and chemical irritation and tooth wear.
Assists smooth air flow, speech and swallowing.
Ion reservoir Solution supersaturated with respect to tooth mineral facilitates
remineralisation of the teeth. Statherin and acidic proline-rich
proteins in saliva inhibit spontaneous precipitation of calcium
phosphate salts.
Buffer Helps to neutralise plaque pH after eating, thus reducing time for
demineralisation.
Cleansing Clears food and aids swallowing.
Antimicrobial
actions
Specific (e.g. sIgA) and non-specific (e.g. Lysozyme,Lactoferrin
and Myeloperoxidase) anti-microbial mechanisms help to control
the oral microflora.
Agglutination Agglutinins in saliva aggregate bacteria, resulting in accelerated
clearance of bacterial cells. Examples are mucins and parotid
saliva glycoproteins.

Pellicle formation Thin (0.5 μm) protective diffusion barrier formed on
enamel from salivary and other proteins.
Digestion The enzyme α-amylase is the most abundant salivary
enzyme; it splits starchy foods into maltose, malto-triose
and dextrins.
Taste Saliva acts as a solvent, thus allowing interaction of
foodstuff with taste buds to facilitate taste
Excretion As the oral cavity is technically outside the body,
substances which are secreted in saliva are excreted.
This is a very inefficient excretory pathway as
reabsorption may occur further down the intestinal tract.
Water balance Under conditions of dehydration, salivary flow is
reduced, dryness of the mouth and information from
osmo-receptors are translated into decreased urine
production and increased drinking.

„APPLIED PHYSIOLOGY
HYPOSALIVATION
 Reduction in the secretion of saliva is called
hyposalivation.
 It is of two types, namely temporary
hyposalivation and permanent hyposalivation.
1. Temporary hyposalivation occurs in:
i. Emotional conditions like fear.
ii. Fever.
iii. Dehydration.

2. Permanent hyposalivation occurs in:
i. Sialolithiasis (obstruction of salivary duct).
ii.Congenital absence or hypoplasia of
salivary glands.
iii. Bell palsy (paralysis of facial nerve).

HYPERSALIVATION
 Excess secretion of saliva is known as
hypersalivation.
 Physiological condition when hypersalivation
occurs is pregnancy. Hypersalivation in
pathological conditions is called ptyalism,
sialorrhea, sialism or sialosis.

 Hypersalivation occurs in the following
pathological conditions:
1. Decay of tooth or neoplasm (abnormal new
growth or tumor) in mouth or tongue due to
continuous irritation of nerve endings in the
mouth.
2. Disease of esophagus, stomach and intestine.

3.Neurological disorders such as cerebral palsy,
mental retardation, cerebral stroke and
parkinsonism.
4.Some psychological and psychiatric conditions.
5.Nausea and vomiting.

OTHER DISORDERS
1. Xerostomia
2. Drooling
3. Chorda tympani syndrome
4. Paralytic secretion of saliva
5. Augmented secretion of saliva
6. Mumps
7. Sjögren syndrome.

1. Xerostomia
 Xerostomia means dry mouth. It is also called
pasties or cottonmouth. It is due to
hyposalivation or absence of salivary secretion
(aptyalism).
 Causes-
i. Dehydration or renal failure.
ii. Sjögren syndrome.
iii. Radiotherapy.
iv. Trauma to salivary gland or their ducts.

v. Side effect of some drugs like antihistamines,
antidepressants, monoamine oxidase inhibitors,
antiparkinsonian drugs and antimuscarinic drugs.
vi. Shock.
vii. After smoking marijuana (psychoactive
compound from the plant Cannabis).
Xerostomia causes difficulties in mastication,
swallowing and speech. It also causes halitosis (bad
breath; exhalation of unpleasant odors).

2. Drooling
 Uncontrolled flow of saliva outside the mouth is
called drooling. It is often called ptyalism.
Causes-
 Drooling occurs because of excess production of
saliva, in association with inability to retain saliva
within the mouth.

 Drooling occurs in the following conditions:
i. During teeth eruption in children.
ii. Upper respiratory tract infection or nasal
allergies in children.
iii. Difficulty in swallowing.
iv. Tonsillitis.
v. Peritonsillar abscess.

3. Chorda Tympani Syndrome
 Chorda tympani syndrome is the condition
characterized by sweating while eating.
 During trauma or surgical procedure, some of the
parasympathetic nerve fibers to salivary glands
may be severed.
 During the regeneration, some of these nerve
fibers, which run along with chorda tympani branch
of facial nerve may deviate and join with the nerve
fibers supplying sweat glands.
 When the food is placed in the mouth, salivary
secretion is associated with sweat secretion.

4. Paralytic Secretion of Saliva
 When the parasympathetic nerve to salivary
gland is cut in experimental animals, salivary
secretion increases for first three weeks and later
diminishes; finally it stops at about sixth week.
 The increased secretion of saliva after cutting the
parasympathetic nerve fibers is called paralytic
secretion. It is because of hyperactivity of
sympathetic nerve fibers to salivary glands after
cutting the parasympathetic fibers.

 These hyperactive sympathetic fibers release
large amount of catecholamines, which induce
paralytic secretion.
 Moreover, the acinar cells of the salivary glands
become hypersensitive to catecholamines after
denervation.
 The paralytic secretion does not occur after the
sympathetic nerve fibers to salivary glands are
cut.

5. Augmented Secretion of Saliva
 If the nerves supplying salivary glands are
stimulated twice, the amount of saliva secreted by
the second stimulus is more than the amount
secreted by the first stimulus.
 It is because, the first stimulus increases
excitability of acinar cells, so that when the second
stimulus is applied, the salivary secretion is
augmented.

6. Mumps
 Mumps is the acute viral infection affecting the
parotid glands.
 The virus causing this disease is Paramyxovirus.
 It is common in children who are not immunized.
 It occurs in adults also.
 Features of mumps are puffiness of cheeks (due
to swelling of parotid glands), fever, sore
 throat and weakness.
 Mumps affects meninges, gonads and pancreas
also.

7. Sjögren Syndrome
 Sjögren syndrome is an autoimmune disorder in
which the immune cells destroy exocrine glands
such as lacrimal glands and salivary glands.
 It is named after Henrik Sjögren who discovered
it. Common symptoms of this syndrome are
dryness of the mouth due to lack of saliva
(xerostomia), persistent cough and dryness of
eyes.

 In some cases, it causes dryness of skin, nose
and vagina. In severe conditions, the organs
like kidneys, lungs, liver, pancreas, thyroid,
blood vessels and brain are affected.

References
 Human Anatomy volume 3 – B D Chaurasia’s
 Text book of Oral Medicine – Anil Govindrao Ghom
 Essential of Medical Physiology sixth edition – K
Sembulingam , Prema Sembulingam
 Text book of Medical Physiology eleventh edition- Guyton
& Hall
 Text book of Histology third edition – Krishna Garg, Indira
Bahl, Mohini Kaul
 Introduction: the anatomy and physiology of salivary
glands - Helen Whelton

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