Deglutition (swallowing) is the process by which food is passed into the stomach from the oral cavity.

1. SWALLOWING
Dr. Ridwana Kawsar
BDS (CMC), BCS (Health)
MS (Conservative Dentistry &Endodontics - BSMMU)
Lecturer, Dept. of Conservative Dentistry & Endodontics
Shaheed Suhrawardy Medical College( ShSMC)
Sher-E-Bangla Nagar, Dhaka

2. Deglutition (swallowing) is the process by which food is
passed into the stomach from the oral cavity.
It is a phenomenon of reflex sequence of muscle contractions
that propels the ingested materials and pooled saliva from
the mouth to the stomach.

3. • The process of swallowing is an essential part of the
digestive process.
• Food is first ingested into the mouth and then broken
down in the mouth by chewing, or mastication, tongue
movements, saliva, and teeth grinding until it becomes
a bolus, a soft mass.
• The food bolus is soft enough that it can easily be
swallowed and propelled through the alimentary canal.

4. Once food is swallowed, from the mouth it moves into
the oropharynx, laryngopharynx, and then passes into the
esophagus and into the stomach.

5. • Swallowing is a reflex activity consisting of muscle
contractions and relaxations that help push the ingested food
and saliva from the mouth to the stomach.
• This reflex activity occurs in coordination with numerous
motor neurons.
• The swallowing reflex is pre-programmed as well as initiated
in the region of the brainstem known as the swallowing
centre.

6. • Although swallowing can be initiated voluntarily, much
of the swallowing occurs without any conscious effort.

7. • The swallowing rate is highest during eating and least
during sleep, and swallowing occurs around 600 times
per day.
• The volume of a swallow in drinking, and probably in
bolus transport, varies from 5 mL in a child to 10–14 mL
in adult women and 15–20 mL in adult men.

8. • Besides helping to move nutrients from the mouth to the stomach,
swallowing has many important protective functions.
• As the respiratory tract and the digestive tract are at the level of
the pharynx and larynx, it becomes crucial that solids and liquids
do not enter the larynx. Protective mechanisms control or inhibit
breathing during swallowing. Vigorous set of reflexes such as
coughing or choking are initiated if food or fluid enters the opening
of the trachea.

9. Types
Infantile/visceral swallow
Adult/Mature swallow

10. Infantile/visceral swallow
• Newborn and infants feed by a process called suckling in
which the intake consists of fluids
• Fetus is capable of sucking and swallowing amniotic fluid in
utero, indicating that the motor programme for these
activities are developed before birth.
• Fetal swallowing takes place at the rate of 7-20 times/day

11. Steps in Infantile/visceral swallow
• In newborn, jaws are apart during the swallow.
• The tongue is placed between the jaws to provide anterior seal.
• The mandible is stabilized mainly by contraction of 7th cranial nerve and the
interposed tongue.
• The lower jaw and tongue are elevated, the tongue is grooved allowing the
milk to flow posteriorly into the pharynx and oesophagus.
• The swallow is guided and to a great extent controlled by sensory interchange
between the lips and the tongue
• Negatve pressure of 50-200 mm of Hg is created during suckling.

12. Usually, by 18 months of age, the following mature swallow
characteristics are to be observed:
The teeth are together;
The mandible is stabilized by contraction of the mandibular elevators,
these being primarily innervated by the trigeminal nerve;
The tongue tip is held against the palate above and behind the
incisors;
There are minimal contractions of the lips during the mature swallow.
MATURE SWALLOW

13. Adult swallowing
Swallowing can be divided into 4 phases
1. Preparatory
2. Oral
3. Pharyngeal
4. Oesophageal
Medulla and lower pons
Voluntery

14. Phase Events
Preparatory Phase Formation of food bolus occurs during this
phase, voluntary process
Oral phase Bolus moves from oral cavity into the
oropharynx; voluntary process
Pharyngeal phase Bolus moves from the oropharynx into the
esophagus; involuntary process
Esophageal phase Bolus moves through the esophagus and
into the stomach; involuntary process

16. 1. PREPARATORY PHASE
• The aim of this phase is to covert the food into aa bolus
which can easily be swallowed
• Food bolus is a round or oval-shaped mass of food formed
in the mouth after thorough chewing.

17. • Starts as soon as liquids are taken into the oral cavity or after the
bolus has been masticated  The liquid or bolus is positioned on the
dorsum of the tongue, with the oral cavity sealed by the lip and the
tongue
• A final characteristic is the stabilization of the oral cavity
• 'Considerable pressure' is exerted between the teeth in the molar
region as the bolus is positioned.

18. • This is a voluntary phase and respiration is stopped for a while in
this phase.
• Once the bolus is positioned on the tongue dorsum, the oral phase begins.
• The lips close and the maxillary and mandible incisors come closer together.
2. ORAL/BUCCAL PHASE

19. • The anterior two-third of the tongue elevate against the maxillary alveolar
ridge and the anterior hard palate, propelling the bolus towards the
pharynx.
• Withdrawal of the soft palate from its rest position against the root of the
tongue, where it is held by the tensor palatini muscles.
• In this phase the soft palate moves upward and the tongue drops
downward and backward.
• The nasopharynx is shut off by the upward movement of the soft palate
and the forward movement of the posterior pharyngeal wall to prevent
regurgitation of food through the nose.

20. • These combined movements make a smooth path for the bolus
as it is pushed from the oral cavity by the peristaltic-Iike action of
the tongue.
• Solid food is actually pushed by the tongue, whereas fluids flow
ahead of the lingual contractions.
• During this phase, the oral cavity maintains an anterior and
lateral seal, and is stabilized by the muscles of mastication.

21. • When a large bolus is to be swallowed, most or all of it is moved
into the preparatory position and is then neatly sectioned by the
tongue in consecutive swallows until the oral cavity is empty.

23. • Next is the pharyngeal phase of swallowing. Unlike the oral phase,
the pharyngeal phase is an involuntary process.
• First, the tongue is blocking the oral cavity. Then, the nasopharynx is
sealed off from the oropharynx and laryngopharynx by elevation of
the soft palate and its uvula.
3. PHARYNGEAL PHASE

25. This phase begins as the bolus passes from the tongue through the
fauces. The pharynx will then receive the bolus after shortening and
widening, at the same time, the larynx will elevate because of the
contraction of suprahyoid muscles and longitudinal pharyngeal
muscles resulting in the epiglottis blocking the trachea. Finally, the
upper esophageal sphincter relaxes and opens, allowing food to enter
the esophagus.

26. • At the beginning of the pharyngeal phase, the posterior part of the
tongue makes a rapid piston-like movement to propel the bolus
through the oropharynx into the hypopharynx.
• The pharyngeal constrictors move upwards and forwards and begin
propelling the bolus through the pharynx by sequential contractions.

27. During the pharyngeal phase, the laryngeal vestibule closes
because of the movement of the epiglottis.

28. The epiglottis does not have to cover the laryngeal opening to
prevent aspiration of food. Aspiration of food generally does not
occur in individuals with an excised epiglottis.
However, the epiglottis does direct the bolus into the piriform
sinuses and, therefore, around the opening of the airway into the
oesophagus

29. • Finally, there is an abrupt elevation of the larynx as the bolus
reaches the laryngo-pharynx and, this is then followed by
elevation of the floor of the laryngophary and opening of the
oesophageal sphincter.

30. Several mechanisms operate to prevent aspiration of the bolus into the airway during
the pharyngeal phase of swallowing.
1. During this phase, respiration is inhibited. Elevation of the larynx and upper
oesophageal sphincter shortens the distance the bolus must travel and hence the
time the bolus is present at the entry of the airway.
2. Intrinsic muscles of the glottis forcefully approximate the vocal cords. The piriform
sinuses create lateral food channels so that the bolus generally deviates around
the laryngeal opening.
3. Any residual bolus material trapped in the piriform sinus after swallowing is
normally at a lower level than the laryngeal vestibule, making aspiration of residual
material unlikely.

32. During this phase, respiration is inhibited, and the epiglottis
blocks off the upper airway to prevent the food bolus and
liquids from entering the airway and being inhaled. If food
does enter the airway, the coughing reflex is triggered. This
can happen if someone talks or inhales while swallowing.

33. • The final stage of deglutition is the esophageal phase. Like the pharyngeal
phase, this process is involuntary.
• Aim of this phase is to make sure that the food enters the oesophagus not the
air passage.
• While peristaltic movement carries the food through the oesophagus, the
hyoid bone, soft palate and tongue return to their 'original positions'.
4. OESOPHAGEAL PHASE

34. After the food is placed in the upper end of oesophagus, the
upper oesophageal sphincter contracts, causing peristaltic
contractions (wave-like movements/ the sequential contractions
of adjacent smooth muscle to propel food in one direction) that
can send the bolus to the stomach with the help of gravity. Once
the food bolus has fully entered the esophagus, the upper
esophageal sphincter will contract and close again.

35. The esophagus pierces the diaphragm at the esophageal hiatus, and
continues to join the stomach at the cardiac orifice, which is
surrounded by the lower esophageal sphincter. It is also known as the
gastroesophageal sphincter or cardiac sphincter.
As the bolus approaches the stomach, the lower esophageal sphincter
around the cardiac orifice will open and allow the food bolus to pass
into the stomach. Once the bolus has entered, the lower esophageal
sphincter will close to prevent regurgitation of stomach contents
therefore protecting the esophagus from acid reflux.

38. • Peristalsis:
• Produced by a series of localized
reflexes in response to distention of
wall by bolus.
• Wave-like muscular contractions:
• Circular smooth muscle contract
behind, relaxes in front of the bolus.
• Followed by longitudinal contraction
(shortening) of smooth muscle.
• Rate of 2-4 cm/sec.

39. MUSCLE ACTIVITY
1. Thirty-one paired muscles are involved in the various phases of swallowing. Muscle patterns
differ with the type of food that is swallowed.
2. Muscle activity in the preparatory and oral phases involves various muscles controlling the face
and mandible. The medial pterygoid, masseter and temporalis muscles are actively involved in
these phases. Facial muscles that control the lips and the cheeks contribute to the development
of an oral seal and stabilization of the mandible.
3. The pharyngeal phase of swallowing is complex, and once it begins, the muscles controlling the
hyoid bone, tongue, pharynx and larynx exhibit a series of contractions, relaxations and
inhibitions. The mylohyoid, geniohyoid, palatopharyngeus, palatoglossus, superior constrictor,
styloglossus and stylohyoid lead the activity at the beginning of a swallow.

40. 4. The pharyngeal constrictors act in an overlapping sequence. The leading complex
is activated and consists of a set of muscles including the mylohyoid, geniohyoid,
posterior tongue, palatopharyngeus, palatoglossus, superior constrictor, styloglossus
and stylohyoid. They are so called because they show activity at the initiation of a
swallow.
5. After the activation of the leading complex, the middle and the inferior constrictor
become active in a sequential order.
6. The thyrohyoid, thyroarytenoid and the cricothyroid muscles begin to contract
after the activity in the leading complex begins to subside.

41. CONTROL OF SWALLOWING
Swallowing can be initiated either voluntarily or by stimulation of various areas
in the oropharynx. The preparatory and oral phases of swallowing are voluntary,
whereas the pharyngeal and oesophageal phases are involuntary. The
swallowing motor sequence, including the motility of the smooth muscles of the
oesophagus, depends on the swallowing centre. The interneurons in this centre
organize the whole sequence of muscle contractions of swallowing so that the
control of swallowing is the property of a precisely interconnected set of
neurons.

42. The swallowing centre comprises three components:
1. Sensory input from the oral cavity, pharynx, larynx and oesophagus terminates in the
nucleus tractus solitarius and trigeminal sensory nucleus that are involved in the initiation of
swallowing, especially the afferent activity in the glossopharyngeal and the superior laryngeal
branch of the vagus nerves.
2. Motor output of the centre derives from motor neurons within the nucleus ambiguus, facial,
trigeminal and hypoglossal motor nuclei as well as motor neurons in the cervical spinal cord.
3. Between the sensory input and motor output of the centre is an interneuronal network that
programs the entire sequence of events in a swallow through excitatory and inhibitory
connections.
The swallowing centre, therefore, is a not a discrete anatomical entity but consists of
brainstem sensory and motor nuclei interconnected by a neuronal network.

43. Neural control of swallowing
Oral phase
The pressure that the food bolus places on the posterior oropharynx
activates the oropharyngeal sensory receptors of
the glossopharyngeal nerve (CN IX), which then send signals to
the solitary nucleus in the swallowing center located in the
lower pons and medulla oblongata of the brainstem. The swallowing
center then outputs signals to initial and control the next two phases
of swallowing, the pharyngeal phase and the esophageal phase.

44. The pharyngeal phase is under autonomic control of the swallowing center located in
the lower pons and medulla oblongata of the brainstem. More specifically, the nucleus
ambiguus in the reticular formation is part of the swallowing center, and it is responsible
for generating general somatic efferent signals.
These nerve impulses are transmitted through various cranial nerves to innervate the
skeletal muscles of the pharynx and upper esophagus that are involved in the
pharyngeal phase of swallowing. It is principally the vagus nerve (CN X) which transmits
these nerve impulses, but five other cranial nerves are also involved in pharyngeal phase
activity: the trigeminal nerve (CN V), the facial nerve (CN VII) the glossopharyngeal nerve
(IX), the accessory nerve (CN XI), and the hypoglossal nerve (CN XII).

46. Suckling
The process by which newborns and infants feed is called suckling; in this process, the intake is
that of fluids. Suckling consists of development of negative pressure or suction in the oral cavity
combined with jaw movements to express milk from the nipple.
Suckling activity in infants and small children is produced by suction and lowering the jaw while
the lips are sealed around the nipple to prevent entry of air into the oral cavity.
The infant first forms a teat from its mother’s breast by sucking the nipple deep into the posterior
part of the mouth to the junction of the hard and soft palates. By elevating the jaw and tongue,
the infant compresses, lengthens and shortens the teat to express milk for swallowing.
Swallowing in the newborn is a liquid swallow and is related to suckling. No teeth are present,
masticatory movements do not occur and semisolid bolus is not formed. The anatomies of the
pharynx and larynx are also different from those of the adult. In the neonate, the soft palate
occupies much of the volume of the upper pharynx, which is more compact than in the adult. The
epiglottis guides the larynx upwards behind the soft palate and remains there during respiration.
During development, the epiglottis descends and assumes its mature functional role during
swallowing. Because of the anatomical relationships of the pharynx and larynx in the newborn, it
has been suggested that infants can swallow without interruption of breathing.