Swallowing, sometimes called deglutition in scientific contexts, is the process in the human or animal body that allows for a substance to pass from the
mouth, to the
pharynx
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its st ...
, and into the
esophagus
The esophagus ( American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to ...
, while shutting the
epiglottis
The epiglottis is a leaf-shaped flap in the throat that prevents food and water from entering the trachea and the lungs. It stays open during breathing, allowing air into the larynx. During swallowing, it closes to prevent aspiration of food in ...
. Swallowing is an important part of
eating
Eating (also known as consuming) is the ingestion of food, typically to provide a heterotrophic organism with energy and to allow for growth. Animals and other heterotrophs must eat in order to survive — carnivores eat other animals, he ...
and
drinking
Drinking is the act of ingesting water or other liquids into the body through the mouth, proboscis, or elsewhere. Humans drink by swallowing, completed by peristalsis in the esophagus. The physiological processes of drinking vary widely am ...
. If the process fails and the material (such as food, drink, or medicine) goes through the
trachea
The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air- breathing animals with lungs. The trachea extends from the ...
, then
choking
Choking, also known as foreign body airway obstruction (FBAO), is a phenomenon that occurs when breathing is impeded by a blockage inside of the respiratory tract. An obstruction that prevents oxygen from entering the lungs results in oxygen dep ...
or
pulmonary aspiration can occur. In the human body the automatic temporary closing of the epiglottis is controlled by the swallowing
reflex.
The portion of food, drink, or other material that will move through the
neck in one swallow is called a bolus.
In
colloquial English
Colloquialism (), also called colloquial language, everyday language or general parlance, is the linguistic style used for casual (informal) communication. It is the most common functional style of speech, the idiom normally employed in conversa ...
, the term "swallowing" is also used to describe the action of taking in a large mouthful of food without any
biting, where the word gulping is more adequate.
In humans
Swallowing comes so easily to most people that the process rarely prompts much thought. However, from the viewpoints of
physiology
Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
, of
speech–language pathology
Speech-language pathology (or speech and language pathology) is a healthcare field of expertise practiced globally. Speech-language pathology (SLP) specializes in the evaluation, diagnosis, treatment, and prevention of communication disorders ...
, and of
health care for people with
difficulty in swallowing (dysphagia), it is an interesting topic with extensive
scientific literature
: ''For a broader class of literature, see Academic publishing.''
Scientific literature comprises scholarly publications that report original empirical and theoretical work in the natural and social sciences. Within an academic field, scie ...
.
Coordination and control
Eating and swallowing are complex neuromuscular activities consisting essentially of three phases, an 'oral, pharyngeal and esophageal phase. Each phase is controlled by a different neurological mechanism. The oral phase, which is entirely voluntary, is mainly controlled by the
medial temporal lobe
The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.
The temporal lobe is involved in pro ...
s and
limbic system of the
cerebral cortex
The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consistin ...
with contributions from the motor cortex and other cortical areas. The pharyngeal swallow is started by the oral phase and subsequently is coordinated by the swallowing center on the
medulla oblongata and
pons
The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum.
The pons is also called the pons Varolii ("bridge of Va ...
. The reflex is initiated by touch receptors in the
pharynx
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its st ...
as a
bolus of food is pushed to the back of the mouth by the tongue, or by stimulation of the palate (palatal reflex).
Swallowing is a complex mechanism using both skeletal muscle (
tongue
The tongue is a muscular organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive process, and is the primary organ of taste. The tongue's upper surface (dorsum) is covered by taste ...
) and smooth muscles of the pharynx and
esophagus
The esophagus ( American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to ...
. The
autonomic nervous system (ANS) coordinates this process in the pharyngeal and esophageal phases.
Phases
Oral phase
Prior to the following stages of the oral phase, the mandible depresses and the lips abduct to allow food or liquid to enter the oral cavity. Upon entering the oral cavity, the mandible elevates and the lips adduct to assist in oral containment of the food and liquid. The following stages describe the normal and necessary actions to form the bolus, which is defined as the state of the food in which it is ready to be swallowed.
1) Moistening
Food is moistened by saliva from the
salivary glands
The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands ( parotid, submandibular, and sublingual), as well as hundreds of minor salivary glands. Salivary gl ...
(
parasympathetic).
2) Mastication
Food is mechanically broken down by the action of the teeth controlled by the muscles of mastication (V
3) acting on the
temporomandibular joint
In anatomy, the temporomandibular joints (TMJ) are the two joints connecting the jawbone to the skull. It is a bilateral synovial articulation between the temporal bone of the skull above and the mandible below; it is from these bones that it ...
. This results in a bolus which is moved from one side of the oral cavity to the other by the tongue.
Buccinator
The buccinator () is a thin quadrilateral muscle occupying the interval between the maxilla and the mandible at the side of the face. It forms the anterior part of the cheek or the lateral wall of the oral cavity.Illustrated Anatomy of the Head ...
(VII) helps to contain the food against the occlusal surfaces of the teeth. The bolus is ready for swallowing when it is held together by saliva (largely mucus), sensed by the
lingual nerve
The lingual nerve carries sensory innervation from the anterior two-thirds of the tongue. It contains fibres from both the mandibular division of the trigeminal nerve (CN V3
) and from the facial nerve (CN VII). The fibres from the trigeminal nerv ...
of the tongue (VII—chorda tympani and IX—lesser petrosal) (V
3). Any food that is too dry to form a bolus will not be swallowed.
3) Trough formation
A trough is then formed at the back of the tongue by the intrinsic muscles (XII). The trough obliterates against the hard palate from front to back, forcing the bolus to the back of the tongue.
The intrinsic muscles of the tongue (XII) contract to make a trough (a longitudinal concave fold) at the back of the tongue. The tongue is then elevated to the roof of the mouth (by the
mylohyoid (mylohyoid nerve—V
3),
genioglossus
The genioglossus is one of the paired extrinsic muscles of the tongue. The genioglossus is the major muscle responsible for protruding (or sticking out) the tongue.
Structure
Genioglossus is the fan-shaped extrinsic tongue muscle that forms the ma ...
,
styloglossus
The styloglossus, the shortest and smallest of the three styloid muscles, arises from the anterior and lateral surfaces of the styloid process near its apex, and from the stylomandibular ligament.
Passing inferiorly and anteriorly between the int ...
and
hyoglossus
The hyoglossus, thin and quadrilateral, arises from the side of the body and from the whole length of the greater cornu of the hyoid bone, and passes almost vertically upward to enter the side of the tongue, between the styloglossus and the inf ...
(the rest XII)) such that the tongue slopes downwards posteriorly. The contraction of the
genioglossus
The genioglossus is one of the paired extrinsic muscles of the tongue. The genioglossus is the major muscle responsible for protruding (or sticking out) the tongue.
Structure
Genioglossus is the fan-shaped extrinsic tongue muscle that forms the ma ...
and
styloglossus
The styloglossus, the shortest and smallest of the three styloid muscles, arises from the anterior and lateral surfaces of the styloid process near its apex, and from the stylomandibular ligament.
Passing inferiorly and anteriorly between the int ...
(both XII) also contributes to the formation of the central trough.
4) Movement of the bolus posteriorly
At the end of the oral preparatory phase, the food bolus has been formed and is ready to be propelled posteriorly into the pharynx. In order for anterior to posterior transit of the bolus to occur, orbicularis oris contracts and adducts the lips to form a tight seal of the oral cavity. Next, the superior longitudinal muscle elevates the apex of the tongue to make contact with the hard palate and the bolus is propelled to the posterior portion of the oral cavity. Once the bolus reaches the
palatoglossal arch
The palatoglossal arch (glossopalatine arch, anterior pillar of fauces) on either side runs downward, lateral (to the side), and forward to the side of the base of the tongue, and is formed by the projection of the glossopalatine muscle with its ...
of the oropharynx, the pharyngeal phase, which is reflex and involuntary, then begins. Receptors initiating this reflex are proprioceptive (afferent limb of reflex is IX and efferent limb is the pharyngeal plexus- IX and X). They are scattered over the base of the tongue, the palatoglossal and palatopharyngeal arches, the tonsillar fossa, uvula and posterior pharyngeal wall. Stimuli from the receptors of this phase then provoke the pharyngeal phase. In fact, it has been shown that the swallowing reflex can be initiated entirely by peripheral stimulation of the internal branch of the
superior laryngeal nerve
The superior laryngeal nerve is a branch of the vagus nerve. It arises from the middle of the inferior ganglion of vagus nerve and in its course receives a branch from the superior cervical ganglion of the sympathetic nervous system.
The superi ...
. This phase is ''voluntary'' and involves important
cranial nerves
Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...
:
V (trigeminal),
VII (facial) and
XII (hypoglossal).
Pharyngeal phase
For the pharyngeal phase to work properly all other egress from the pharynx must be occluded—this includes the
nasopharynx
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struct ...
and the
larynx. When the pharyngeal phase begins, other activities such as chewing, breathing, coughing and vomiting are concomitantly inhibited.
5) Closure of the nasopharynx
The soft palate is tensed by
tensor palatini (Vc), and then elevated by
levator palati
The levator veli palatini () is the elevator muscle of the soft palate in the human body. It is supplied via the pharyngeal plexus. During swallowing, it contracts, elevating the soft palate to help prevent food from entering the nasopharynx.
...
ni (pharyngeal plexus—IX, X) to close the nasopharynx. There is also the simultaneous approximation of the walls of the pharynx to the posterior free border of the soft palate, which is carried out by the palatopharyngeus (pharyngeal plexus—IX, X) and the upper part of the superior constrictor (pharyngeal plexus—IX, X).
6) The pharynx prepares to receive the bolus
The pharynx is pulled upwards and forwards by the
suprahyoid and longitudinal pharyngeal muscles –
stylopharyngeus
The stylopharyngeus is a muscle in the head that stretches between the temporal styloid process and the pharynx.
Structure
The stylopharyngeus is a long, slender muscle, cylindrical above, flattened below. It arises from the medial side of the ...
(IX),
salpingopharyngeus (pharyngeal plexus—IX, X) and
palatopharyngeus
The palatopharyngeus (palatopharyngeal or pharyngopalatinus) muscle is a small muscle in the roof of the mouth.
It is a long, fleshy fasciculus, narrower in the middle than at either end, forming, with the mucous membrane covering its surface, the ...
(pharyngeal plexus—IX, X) to receive the bolus. The palatopharyngeal folds on each side of the pharynx are brought close together through the superior constrictor muscles, so that only a small bolus can pass.
7) Opening of the
auditory tube
Auditory means of or relating to the process of hearing:
* Auditory system, the neurological structures and pathways of sound perception
** Auditory bulla, part of auditory system found in mammals other than primates
** Auditory nerve, also known ...
The actions of the
levator palati
The levator veli palatini () is the elevator muscle of the soft palate in the human body. It is supplied via the pharyngeal plexus. During swallowing, it contracts, elevating the soft palate to help prevent food from entering the nasopharynx.
...
ni (pharyngeal plexus—IX, X),
tensor palatini (Vc) and
salpingopharyngeus (pharyngeal plexus—IX, X) in the closure of the nasopharynx and elevation of the pharynx opens the auditory tube, which equalises the pressure between the nasopharynx and the middle ear. This does not contribute to swallowing, but happens as a consequence of it.
8) Closure of the
oropharynx
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struc ...
The oropharynx is kept closed by palatoglossus (pharyngeal plexus—IX, X), the intrinsic muscles of tongue (XII) and styloglossus (XII).
9) Laryngeal closure
The primary laryngopharyngeal protective mechanism to prevent aspiration during swallowing is via the closure of the true vocal folds. The adduction of the vocal cords is affected by the contraction of the
lateral cricoarytenoids and the oblique and transverse
arytenoids
The arytenoid cartilages () are a pair of small three-sided pyramids which form part of the larynx. They are the site of attachment of the vocal cords. Each is pyramidal or ladle-shaped and has three surfaces, a base, and an apex. The arytenoid ...
(all recurrent laryngeal nerve of vagus). Since the true vocal folds adduct during the swallow, a finite period of apnea (swallowing apnea) must necessarily take place with each swallow. When relating swallowing to respiration, it has been demonstrated that swallowing occurs most often during expiration, even at full expiration a fine air jet is expired probably to clear the upper larynx from food remnants or liquid. The clinical significance of this finding is that patients with a baseline of compromised lung function will, over a period of time, develop respiratory distress as a meal progresses.
Subsequently, false vocal fold adduction, adduction of the aryepiglottic folds and retroversion of the epiglottis take place. The aryepiglotticus (recurrent laryngeal nerve of vagus) contracts, causing the arytenoids to appose each other (closes the laryngeal aditus by bringing the aryepiglottic folds together), and draws the epiglottis down to bring its lower half into contact with arytenoids, thus closing the aditus. Retroversion of the epiglottis, while not the primary mechanism of protecting the airway from laryngeal penetration and aspiration, acts to anatomically direct the food bolus laterally towards the
piriform fossa.
Additionally, the larynx is pulled up with the pharynx under the tongue by stylopharyngeus (IX), salpingopharyngeus (pharyngeal plexus—IX, X), palatopharyngeus (pharyngeal plexus—IX, X) and inferior constrictor (pharyngeal plexus—IX, X). This phase is ''passively'' controlled reflexively and involves cranial nerves V,
X (vagus),
XI (accessory) and
XII (hypoglossal). The
respiratory center of the medulla is directly inhibited by the swallowing center for the very brief time that it takes to swallow. This means that it is briefly impossible to breathe during this phase of swallowing and the moment where breathing is prevented is known as ''deglutition
apnea''.
10)
Hyoid
The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical vertebra. ...
elevation
The hyoid is elevated by digastric (V & VII) and stylohyoid (VII), lifting the pharynx and larynx up even further.
11) Bolus transits pharynx
The bolus moves down towards the esophagus by pharyngeal
peristalsis
Peristalsis ( , ) is a radially symmetrical contraction and relaxation of muscles that propagate in a wave down a tube, in an anterograde direction. Peristalsis is progression of coordinated contraction of involuntary circular muscles, whic ...
which takes place by sequential contraction of the superior, middle and inferior pharyngeal constrictor muscles (pharyngeal plexus—IX, X). The lower part of the inferior constrictor (
cricopharyngeus) is normally closed and only opens for the advancing bolus. Gravity plays only a small part in the upright position—in fact, it is possible to swallow solid food even when standing on one’s head. The velocity through the pharynx depends on a number of factors such as viscosity and volume of the bolus. In one study, bolus velocity in healthy adults was measured to be approximately 30–40 cm/s.
Esophageal phase
12) Esophageal peristalsis
Like the pharyngeal phase of swallowing, the esophageal phase of swallowing is under involuntary neuromuscular control. However, propagation of the food bolus is significantly slower than in the pharynx. The bolus enters the esophagus and is propelled downwards first by striated muscle (recurrent laryngeal, X) then by the smooth muscle (X) at a rate of 3–5 cm/s. The upper esophageal sphincter relaxes to let food pass, after which various striated constrictor muscles of the pharynx as well as peristalsis and relaxation of the
lower esophageal sphincter
The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...
sequentially push the bolus of food through the esophagus into the stomach.
13) Relaxation phase
Finally the larynx and pharynx move down with the hyoid mostly by elastic recoil. Then the larynx and pharynx move down from the hyoid to their relaxed positions by elastic recoil.
Swallowing therefore depends on coordinated interplay between many various muscles, and although the initial part of swallowing is under voluntary control, once the deglutition process is started, it is quite hard to stop it.
Clinical significance
Swallowing becomes a great concern for the elderly since
strokes and
Alzheimer's disease can interfere with the
autonomic nervous system.
Speech pathologists commonly diagnose and treat this condition since the speech process uses the same neuromuscular structures as swallowing. Diagnostic procedures commonly performed by a speech pathologist to evaluate dysphagia include Fiberoptic Endoscopic Evaluation of Swallowing and Modified Barium Swallow Study. Occupational Therapists may also offer swallowing rehabilitation services as well as prescribing modified feeding techniques and utensils. Consultation with a dietician is essential, in order to ensure that the individual with dysphagia is able to consume sufficient calories and nutrients to maintain health. In terminally ill patients, a failure of the reflex to swallow leads to a build-up of mucus or saliva in the throat and airways, producing a noise known as a
death rattle
Terminal respiratory secretions (or simply terminal secretions),, known colloquially as a death rattle, are sounds often produced by someone who is near death as a result of fluids such as saliva and bronchial secretions accumulating in the throa ...
(not to be confused with
agonal respiration, which is an abnormal pattern of breathing due to cerebral ischemia or hypoxia).
Abnormalities of the pharynx and/or oral cavity may lead to
oropharyngeal dysphagia
Oropharyngeal dysphagia arises from abnormalities of muscles, nerves or structures of the oral cavity, pharynx, and upper esophageal sphincter.
Signs and symptoms
Some signs and symptoms of swallowing difficulties include difficulty controlling f ...
. Abnormalities of the esophagus may lead to
esophageal dysphagia
Esophageal dysphagia is a form of dysphagia where the underlying cause arises from the body of the esophagus, lower esophageal sphincter, or cardia of the stomach, usually due to mechanical causes or motility problems.
Signs and symptoms
Patients ...
.
The failure of the lower esophagus sphincter to respond properly to swallowing is called
achalasia
Esophageal achalasia, often referred to simply as achalasia, is a failure of smooth muscle fibers to relax, which can cause the lower esophageal sphincter to remain closed. Without a modifier, "achalasia" usually refers to achalasia of the esoph ...
.
M-Type Swallowing
With practice, people can learn to swallow fluidly without closing the mouth by merely manipulating the tongue and jaw to drive fluids or foods down the esophagus. With a continuous motion, an individual forges breathing and priorities the swallowed matter. This intermediate level of muscle manipulation is similar to the techniques used by sword swallowers.
In non-mammal animals
![Pelican swallowing a fish part 4](https://upload.wikimedia.org/wikipedia/commons/a/a2/Pelican_swallowing_a_fish_part_4.JPG)
In many birds, the esophagus is largely a mere
gravity chute, and in such events as a
seagull swallowing a fish or a
stork swallowing a
frog
A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" ''Triadobatrachus'' is ...
, swallowing consists largely of the bird lifting its head with its beak pointing up and guiding the prey with tongue and jaws so that the prey slides inside and down.
In
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...
, the tongue is largely bony and much less mobile and getting the food to the back of the pharynx is helped by pumping water in its mouth and out of its
gill
A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
s.
In
snake
Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...
s, the work of swallowing is done by raking with the lower jaw until the prey is far enough back to be helped down by body undulations.
See also
*
Dysphagia
Dysphagia is difficulty in swallowing. Although classified under "symptoms and signs" in ICD-10, in some contexts it is classified as a condition in its own right.
It may be a sensation that suggests difficulty in the passage of solids or liq ...
*
Occlusion
Occlusion may refer to:
Health and fitness
* Occlusion (dentistry), the manner in which the upper and lower teeth come together when the mouth is closed
* Occlusion miliaria, a skin condition
* Occlusive dressing, an air- and water-tight trauma ...
*
Speech and language pathology
Speech is a human vocal communication using language. Each language uses phonetic combinations of vowel and consonant sounds that form the sound of its words (that is, all English words sound different from all French words, even if they are th ...
References
External links
*
Overview at nature.comAnatomy and physiology of swallowing at dysphagia.comSwallowing animation (flash) at hopkins-gi.org
*
rticle on French WikipediaSee : "
déglutition atypique" = unfunctional or pathological swallowing.
Normal Swallowing and Dysphagia: Pediatric Population
{{Authority control
Reflexes
Physiology
Articles containing video clips