Swallowing
Encyclopedia
Swallowing, known scientifically as deglutition, is the process in the human or animal body that makes something pass from the mouth
, to the pharynx
, and into the esophagus
, while shutting the epiglottis
. If this fails and the object goes through the trachea
, then choking
or pulmonary aspiration
can occur. In the human body it is controlled by the swallowing reflex
.
temporal lobe
s and limbic system
of the cerebral cortex
with contributions from the motor cortex and other cortical areas. The pharyngeal swallow is started by the oral phase and subsequently is co-ordinated by the swallowing center in the medulla oblongata
and pons
. The reflex is initiated by touch receptors in the pharynx
as a bolus
of food is pushed to the back of the mouth by the tongue.
Swallowing is a complex mechanism using both skeletal muscle (tongue
) and smooth muscles of the pharynx and esophagus
. The autonomic nervous system
(ANS) coordinates this process in the pharyngeal and esophageal phases.
1) Moistening
Food is moistened by saliva from the salivary glands (parasympathetic).
2) Mastication
Food is mechanically broken down by the action of the teeth controlled by the muscles of mastication (Vc) acting on the temporomandibular joint
. This results in a bolus which is moved from one side of the oral cavity to the other by the tongue. Buccinator
(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 (largely mucus) saliva (VII—chorda tympani and IX—lesser petrosal), sensed by the lingual nerve
of the tongue (Vc). 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—Vc), genioglossus
, styloglossus
and hyoglossus
(the rest XII)) such that the tongue slopes downwards posteriorly. The contraction of the genioglossus
and styloglossus
(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 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
. This phase is voluntary and involves important cranial nerves
: V (trigeminal)
, VII (facial)
and XII (hypoglossal)
.
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 palati (Vc), and then elevated by levator palati (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 (IX), salpingopharyngeus (pharyngeal plexus—IX, X) and palatopharyngeus (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
The actions of the levator palati (pharyngeal plexus—IX, X), tensor palati (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 oropharynx is kept closed by palatoglossus (pharyngeal plexus—IX, X), the intrinsic muscles of tongue (XII) and styloglossus (XII).
9) Laryngeal closure
It is true vocal fold closure that is the primary laryngopharyngeal protective mechanism to prevent aspiration during swallowing. The adduction of the vocal cords are effected by the contraction of the lateral cricoarytenoids and the oblique and transverse arytenoids (all recurrent laryngeal nerve of vagus). Since the true vocal folds adduct during the swallow, a finite period of apnea must necessarily take place with each swallow. When relating swallowing to respiration, it has been demonstrated that swallowing occurs most often during expiration. 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 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
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.
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/sec. 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
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.
s and Alzheimer's disease
can interfere with the autonomic nervous system
. Speech therapy is commonly used to correct this condition since the speech process uses the same neuromuscular structures as swallowing. 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
, or agonal respiration
.
Abnormalities of the pharynx and/or oral cavity may lead to oropharyngeal dysphagia
. Abnormalities of the esophagus may lead to esophageal dysphagia
.
The failure of the lower esophagous sphincter to respond properly to swallowing is called achalasia
.
swallowing a frog
, 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
, 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
s.
In snake
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.
Mouth
The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....
, to the pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
, and into the esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
, while shutting the epiglottis
Epiglottis
The epiglottis is a flap that is made of elastic cartilage tissue covered with a mucous membrane, attached to the entrance of the larynx. It projects obliquely upwards behind the tongue and the hyoid bone, pointing dorsally. The term, like tonsils, is often incorrectly used to refer to the uvula...
. If this fails and the object goes through the trachea
Vertebrate trachea
In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...
, then choking
Choking
Choking is the mechanical obstruction of the flow of air from the environment into the lungs. Choking prevents breathing, and can be partial or complete, with partial choking allowing some, although inadequate, flow of air into the lungs. Prolonged or complete choking results in asphyxia which...
or pulmonary aspiration
Pulmonary aspiration
Pulmonary aspiration is the entry of material from the oropharynx or gastrointestinal tract into the larynx and lower respiratory tract...
can occur. In the human body it is controlled by the swallowing reflex
Reflex
A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. A true reflex is a behavior which is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.-See also:...
.
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 medialMedial
- Medial magmas :In abstract algebra, a medial magma is a set with a binary operation which satisfies the identity \cdot = \cdot , or more simply, xy\cdot uv = xu\cdot yv...
temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
s and limbic system
Limbic system
The limbic system is a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, septum, limbic cortex and fornix, which seemingly support a variety of functions including emotion, behavior, long term memory, and olfaction. The term "limbic" comes from the Latin...
of the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
with contributions from the motor cortex and other cortical areas. The pharyngeal swallow is started by the oral phase and subsequently is co-ordinated by the swallowing center in the medulla oblongata
Medulla oblongata
The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...
and pons
Pons
The pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio . It is superior to the medulla oblongata, inferior to the midbrain, and ventral to the cerebellum. In humans and other bipeds this means it...
. The reflex is initiated by touch receptors in the pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
as a bolus
Bolus (digestion)
In digestion, a bolus is a mass of food that has been chewed at the point of swallowing. Once a bolus reaches the stomach, digestion begins....
of food is pushed to the back of the mouth by the tongue.
Swallowing is a complex mechanism using both skeletal muscle (tongue
Tongue
The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...
) and smooth muscles of the pharynx and esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
. The autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
(ANS) coordinates this process in the pharyngeal and esophageal 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 (parasympathetic).
2) Mastication
Food is mechanically broken down by the action of the teeth controlled by the muscles of mastication (Vc) acting on the temporomandibular joint
Temporomandibular joint
The temporomandibular joint is the joint of the jaw and is frequently referred to as TMJ. There are two TMJs, one on either side, working in unison. The name is derived from the two bones which form the joint: the upper temporal bone which is part of the cranium , and the lower jaw bone called the...
. This results in a bolus which is moved from one side of the oral cavity to the other by the tongue. Buccinator
Buccinator muscle
The buccinator is a thin quadrilateral muscle, occupying the interval between the maxilla and the mandible at the side of the face.-Action:Its purpose is to pull back the angle of the mouth and to flatten the cheek area, which aids in holding the cheek to the teeth during chewing.It aids whistling...
(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 (largely mucus) saliva (VII—chorda tympani and IX—lesser petrosal), sensed by the lingual nerve
Lingual nerve
The lingual nerve is a branch of the mandibular nerve , itself a branch of the trigeminal nerve, which supplies sensory innervation to the tongue...
of the tongue (Vc). 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
Mylohyoid can refer to:* Mylohyoid muscle* Mylohyoid line* Mylohyoid nerve* Mylohyoid branch of inferior alveolar artery* Mylohyoid groove...
(mylohyoid nerve—Vc), genioglossus
Genioglossus
The genioglossus is a muscle of the human body which runs from the chin to the tongue. The genioglossus is the major muscle responsible for protruding the tongue.-Structure:...
, styloglossus
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....
and hyoglossus
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 Longitudinalis inferior....
(the rest XII)) such that the tongue slopes downwards posteriorly. The contraction of the genioglossus
Genioglossus
The genioglossus is a muscle of the human body which runs from the chin to the tongue. The genioglossus is the major muscle responsible for protruding the tongue.-Structure:...
and styloglossus
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....
(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 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
Superior laryngeal nerve
The superior laryngeal nerve is a branch of the vagus nerve. It arises from the middle of the ganglion nodosum and in its course receives a branch from the superior cervical ganglion of the sympathetic....
. This phase is voluntary and involves important cranial nerves
Cranial nerves
Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...
: V (trigeminal)
Trigeminal nerve
The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...
, VII (facial)
Facial nerve
The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...
and XII (hypoglossal)
Hypoglossal nerve
The hypoglossal nerve is the twelfth cranial nerve , leading to the tongue. The nerve arises from the hypoglossal nucleus and emerges from the medulla oblongata in the preolivary sulcus separating the olive and the pyramid. It then passes through the hypoglossal canal...
.
Pharyngeal phase
For the pharyngeal phase to work properly all other egress from the pharynx must be occluded—this includes the nasopharynxNasopharynx
The nasopharynx is the uppermost part of the pharynx. It extends from the base of the skull to the upper surface of the soft palate; it differs from the oral and laryngeal parts of the pharynx in that its cavity always remains patent .-Lateral:On its lateral wall is the pharyngeal ostium of the...
and the larynx
Larynx
The larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...
. 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 palati (Vc), and then elevated by levator palati (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 (IX), salpingopharyngeus (pharyngeal plexus—IX, X) and palatopharyngeus (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
The actions of the levator palati (pharyngeal plexus—IX, X), tensor palati (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
Oropharynx
The Oropharynx reaches from the Uvula to the level of the hyoid bone.It opens anteriorly, through the isthmus faucium, into the mouth, while in its lateral wall, between the two palatine arches, is the palatine tonsil....
The oropharynx is kept closed by palatoglossus (pharyngeal plexus—IX, X), the intrinsic muscles of tongue (XII) and styloglossus (XII).
9) Laryngeal closure
It is true vocal fold closure that is the primary laryngopharyngeal protective mechanism to prevent aspiration during swallowing. The adduction of the vocal cords are effected by the contraction of the lateral cricoarytenoids and the oblique and transverse arytenoids (all recurrent laryngeal nerve of vagus). Since the true vocal folds adduct during the swallow, a finite period of apnea must necessarily take place with each swallow. When relating swallowing to respiration, it has been demonstrated that swallowing occurs most often during expiration. 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)
Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
, XI (accessory)
Accessory nerve
In anatomy, the accessory nerve is a nerve that controls specific muscles of the shoulder and neck. As part of it was formerly believed to originate in the brain, it is considered a cranial nerve...
and XII (hypoglossal)
Hypoglossal nerve
The hypoglossal nerve is the twelfth cranial nerve , leading to the tongue. The nerve arises from the hypoglossal nucleus and emerges from the medulla oblongata in the preolivary sulcus separating the olive and the pyramid. It then passes through the hypoglossal canal...
. 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
Apnea
Apnea, apnoea, or apnœa is a term for suspension of external breathing. During apnea there is no movement of the muscles of respiration and the volume of the lungs initially remains unchanged...
.
10) Hyoid 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
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...
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 peristalsisLike 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/sec. 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
Cardia
The cardia is the anatomical term for the part of the stomach attached to the esophagus. The cardia begins immediately distal to the z-line of the gastroesophageal junction, where the squamous epithelium of the esophagus gives way to the columnar epithelium of the gastrointestinal tract.Just...
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 strokeStroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
s and Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
can interfere with the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
. Speech therapy is commonly used to correct this condition since the speech process uses the same neuromuscular structures as swallowing. 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
Death rattle
A death rattle is a medical term that describes the sound produced by someone who is near death when saliva accumulates in the throat. Those who are dying may lose their ability to swallow, resulting in such an accumulation...
, or agonal respiration
Agonal respiration
Agonal respiration is an abnormal pattern of breathing characterized by gasping, labored breathing, accompanied by strange vocalizations and myoclonus. Possible causes include cerebral ischemia, extreme hypoxia or even anoxia...
.
Abnormalities of the pharynx and/or oral cavity may lead to oropharyngeal dysphagia
Oropharyngeal dysphagia
Swallowing disorders can occur in all age groups, resulting from congenital abnormalities, structural damage, and/or medical conditions. Swallowing problems are a common complaint among older individuals, and the incidence of dysphagia is higher in the elderly, in patients who have had strokes, and...
. Abnormalities of the esophagus may lead to esophageal dysphagia
Esophageal dysphagia
Esophageal dysphagia arises from the body of the esophagus, lower esophageal sphincter, or cardia of the stomach, usually due to mechanical causes or motility problems.-Symptoms, signs, and evaluation:...
.
The failure of the lower esophagous sphincter to respond properly to swallowing is called achalasia
Achalasia
Achalasia , also known as esophageal achalasia, achalasia cardiae, cardiospasm, and esophageal aperistalsis, is an esophageal motility disorder involving the smooth muscle layer of the esophagus and the lower esophageal sphincter...
.
In animals
In many birds, the esophagus is largely merely a gravity chute, and in such events as a seagull swallowing a fish or a storkStork
Storks are large, long-legged, long-necked wading birds with long, stout bills. They belong to the family Ciconiidae. They are the only family in the biological order Ciconiiformes, which was once much larger and held a number of families....
swallowing a frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
, 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
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate 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...
, 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
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s.
In snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
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
- DysphagiaDysphagiaDysphagia is the medical term for the symptom of difficulty in swallowing. Although classified under "symptoms and signs" in ICD-10, the term is sometimes used as a condition in its own right. Sufferers are sometimes unaware of their dysphagia....
- OcclusionOcclusion (dentistry)Occlusion, in a dental context, means simply the contact between teeth. More technically, it is the relationship between the maxillary and mandibular teeth when they approach each other, as occurs during chewing or at rest....
- Speech and language pathologySpeech and language pathologySpeech-Language Pathology specializes in communication disorders.The main components of speech production include: phonation, the process of sound production; resonance, opening and closing of the vocal folds; intonation, the variation of pitch; and voice, including aeromechanical components of...
External links
- Overview at nature.com
- Anatomy and physiology of swallowing at dysphagia.com
- Swallowing animation (flash) at hopkins-gi.org
- [Article on french Wikipedia] See : "déglutition atypique" = unfunctional or pathological swallowing.