ORAL CAVITY
SALIVA SECRETION
SWALLOWING
Lecture 2
Dr. Zahoor Ali Shaikh
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ORAL CAVITY
 Entry to GIT is through the mouth or oral cavity.
 In mouth, we have:
LIPS
 These are muscular, help to keep the food in mouth.
 Lips have non-digestive function also e.g. help in speech, have
sensory receptors.
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ORAL CAVITY
PALATE
 It forms the roof of the oral cavity and separates the mouth
from the nasal passages.
 Palate allows breathing and chewing to take place at the same
time.
 At the end of palate, there is UVULA.
 NOTE – During swallowing one has to stop breathing.
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ORAL CAVITY
TONGUE
 It forms the floor of the oral cavity, it is composed of
voluntarily controlled skeletal muscles.
 Movements of tongue help in guiding food within the mouth.
 Tongue plays important role in speech.
 Taste buds [e.g. sweet, bitter] are located at the tongue.
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ORAL CAVITY
PHARYNX
 It is the cavity at the throat.
 It acts common path for both digestive system [mouth and
esophagus for food] and respiratory system [link between
nasal passages and trachea for air].
 In the side walls of pharynx are tonsils, lymphoid tissues, part
of body’s defense.
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ORAL CAVITY
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TEETH
Teeth are responsible for process of mastication or chewing.
Teeth are embedded in jaw bones.
Chewing helps in breaking the food into smaller pieces to
facilitate swallowing and increase food surface area where
salivary enzymes can act.
Chewing helps to mix food with saliva.
SALIVA
 It is secretion produced by salivary glands.
 Daily secretion about 1000ml– 1500ml
 There are 3 pairs of salivary glands which produce saliva,
they lie outside oral cavity and discharge saliva through ducts
in the mouth. They are:
 i). Parotid Glands
 ii). Submandibular Glands
 iii). Sublingual Glands
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COMPOSITION OF SALIVA
 Water – 99.5%
 Electrolyte & Protein – 0.5%
 pH – 7
 Salivary protein are amylase, mucus, lysozyme.
 Saliva contains two major types of protein secretion:
 1. Serous secretion – contains α-amylase [ptyalin] enzyme for
digesting starch.
 2. Mucus secretion – that contains mucin for protection and
lubrication.
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COMPOSITION OF SALIVA
 Parotid gland secrete serous type of secretion.
 Submandibular gland secrete both i.e. serous and mucus
secretion.
 Sublingual Glands secrete mainly mucus.
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COMPOSITION OF SALIVA
 Saliva is secreted in the acini is nearly isotonic to the plasma.
 During passage through the ducts, the composition of saliva
is modified as Na+ and Cl- are absorbed and K+ and HCO3
are secreted.
 The ducts are relatively impermeable to water.
 Therefore, saliva that reaches the mouth is HYPOTONIC,
rich in K+, but depleted of Na+ and Cl-.
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FUNCTIONS OF SALIVA
1. Helps in digestion of carbohydrates in mouth through action
of salivary amylase, an enzyme that breaks polysaccharide
into maltose [disaccharide].
2. Helps in swallowing by providing lubrication due to presence
of mucus.
3. Anti-bacterial action due to presence of lysozyme, an enzyme
that destroys bacteria.
4. Acts as solvent for molecules that stimulate taste-buds
[present on the tongue].
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FUNCTIONS OF SALIVA
5. Helps in speech [it is difficult to talk when mouth is dry].
6. Helps in oral hygiene by keeping mouth and teeth clean.
7. Saliva is rich in bicarbonates which neutralizes acids in food.
8. Prevents dental caries.
9. Saliva contain IGA
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SALIVA
 Is Saliva essential for digestion?
 Not essential for digestion because enzymes produced by
pancreas and small intestine can complete food digestion
even in the absence of salivary secretion.
 CLINICAL
 Decreased salivary secretion is called ‘XEROSTOMIA’. It
causes dryness of mouth, therefore, difficulty in chewing,
swallowing, speech, increase in dental caries.
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SALIVARY SECRETION
 Salivary secretion increased with different stimuli.
 It is maximum with lemon [4 to 5ml/min].
 There is continuous basal secretion of saliva [0.5ml/min] due
to stimulation of parasympathetic nerve ending to salivary
glands.
 Salivary secretion is increased by:
 (i). Simple Reflex
 (ii). Conditioned Reflex
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SALIVARY SECRETION
(i). Simple Salivary Reflex
 When we take food, chemoreceptors and pressure receptors
in oral cavity are stimulated.
 Afferent nerve carry impulse to salivary center in Medulla
[brain stem], it send impulse via autonomic nerves to salivary
glands and increase salivary secretion.
(ii). Conditioned Reflex
 It occurs without taking food, but just thinking, seeing,
smelling of food.
 Reflex occurs through cerebral cortex to stimulate
medullary salivary center.
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Control of Salivary Secretion
 Both parasympathetic and sympathetic ANS supply salivary
glands and increase salivary secretion.
 The quantity, characteristic, and mechanism of saliva
production by parasympathetic and sympathetic are different.
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Control of Salivary Secretion
 Parasympathetic – produces increased amount of watery
saliva rich in enzymes.
 Sympathetic – produces small increase of thick saliva, rich
in mucus.
 IMPORTANT – control of salivary secretion is NEURAL
only [other digestive secretion are regulated by nervous
system and hormones].
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SWALLOWING
 Swallowing mean moving the food from the mouth through
esophagus into the stomach.
 Swallowing is all or none reflex.
 Swallowing is initiated when a bolus or chewed food or liquid
is voluntarily forced by the tongue to the back of mouth into
the pharynx.
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SWALLOWING
 Pharyngeal pressure receptors send afferent impulses to the
swallowing center located in the medulla of brain stem.
 Swallowing center activates the muscles involved in
swallowing.
 Swallowing is initiated voluntarily but once began, it can not
be stopped.
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SWALLOWING
 Swallowing has three stages:
1. Oral Stage - voluntary
2. Pharyngeal Stage – involuntary
3. Esophageal Stage – involuntary
 Oropharyngeal Stage
 It last for 1 to 2 second and consist of moving the bolus from
the mouth through the pharynx into the esophagus.
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SWALLOWING
 Oropharyngeal Stage {cont}
 When bolus [food] enters the pharynx, it is directed into the
esophagus and prevented from entering the trachea or nasal
passages.
 Food is prevented from entering the nasal passages by
elevation of soft palate and uvula sealing off the nasal passages
from the pharynx so that food does not enter the nose.
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SWALLOWING
 Oropharyngeal Stage {cont}
 Food is prevented from entering the trachea by elevation of
larynx and tight closure of vocal cords across the laryngeal
opening or glottis.
 Epiglottis – cartilaginous tissue prevents the food from
entering the trachea.
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SWALLOWING
 During swallowing, respiration ceases, as respiratory passages
are sealed off and swallowing center briefly inhibits the
respiratory center in medulla.
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WHAT YOU SHOULD KNOW FROM THIS
LECTURE
 Oral Cavity
 Saliva
 Salivary Glands
 Composition of Saliva
 Functions of Saliva
 Salivary Secretion
 Neural Control
 XEROSTOMIA
 Swallowing
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THANK YOU
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