In the mouth, the tongue and the teeth begin mechanical digestion, and saliva begins chemical digestion. The pharynx, which plays roles in breathing and vocalization as well as digestion, runs from the nasal and oral cavities superiorly to the esophagus inferiorly (for digestion) and to the larynx anteriorly (for respiration). During deglutition (swallowing), the soft palate rises to close off the nasopharynx, the larynx elevates, and the epiglottis folds over the glottis. The esophagus includes an upper esophageal sphincter made of skeletal muscle, which regulates the movement of food from the pharynx to the esophagus. It also has a lower esophageal sphincter, made of smooth muscle, which controls the passage of food from the esophagus to the stomach. Cells in the esophageal wall secrete mucus that eases the passage of the food bolus.
bolus
mass of chewed food
cementum
bone-like tissue covering the root of a tooth
crown
portion of tooth visible superior to the gum line
cuspid
(also, canine) pointed tooth used for tearing and shredding food
deciduous tooth
one of 20 “baby teeth”
deglutition
three-stage process of swallowing
dens
tooth
dentin
bone-like tissue immediately deep to the enamel of the crown or cementum of the root of a tooth
dentition
set of teeth
enamel
covering of the dentin of the crown of a tooth
esophagus
muscular tube that runs from the pharynx to the stomach
fauces
opening between the oral cavity and the oropharynx
gingiva
gum
incisor
midline, chisel-shaped tooth used for cutting into food
labium
lip
labial frenulum
midline mucous membrane fold that attaches the inner surface of the lips to the gums
laryngopharynx
part of the pharynx that functions in respiration and digestion
lingual frenulum
mucous membrane fold that attaches the bottom of the tongue to the floor of the mouth
lingual lipase
digestive enzyme from glands in the tongue that acts on triglycerides
lower esophageal sphincter
smooth muscle sphincter that regulates food movement from the esophagus to the stomach
molar
tooth used for crushing and grinding food
oral cavity
(also, buccal cavity) mouth
oral vestibule
part of the mouth bounded externally by the cheeks and lips, and internally by the gums and teeth
oropharynx
part of the pharynx continuous with the oral cavity that functions in respiration and digestion
palatoglossal arch
muscular fold that extends from the lateral side of the soft palate to the base of the tongue
palatopharyngeal arch
muscular fold that extends from the lateral side of the soft palate to the side of the pharynx
parotid gland
one of a pair of major salivary glands located inferior and anterior to the ears
permanent tooth
one of 32 adult teeth
pharynx
throat
premolar
(also, bicuspid) transitional tooth used for mastication, crushing, and grinding food
pulp cavity
deepest portion of a tooth, containing nerve endings and blood vessels
root
portion of a tooth embedded in the alveolar processes beneath the gum line
saliva
aqueous solution of proteins and ions secreted into the mouth by the salivary glands
salivary amylase
digestive enzyme in saliva that acts on starch
salivary gland
an exocrine gland that secretes a digestive fluid called saliva
salivation
secretion of saliva
soft palate
posterior region of the bottom portion of the nasal cavity that consists of skeletal muscle
sublingual gland
one of a pair of major salivary glands located beneath the tongue
submandibular gland
one of a pair of major salivary glands located in the floor of the mouth
tongue
accessory digestive organ of the mouth, the bulk of which is composed of skeletal muscle
upper esophageal sphincter
skeletal muscle sphincter that regulates food movement from the pharynx to the esophagus
voluntary phase
initial phase of deglutition, in which the bolus moves from the mouth to the oropharynx
Watch this animation to see how swallowing is a complex process that involves the nervous system to coordinate the actions of upper respiratory and digestive activities. During which stage of swallowing is there a risk of food entering respiratory pathways and how is this risk blocked?
Answers may vary.
1. Which of these ingredients in saliva is responsible for activating salivary amylase?
A) mucus
B) phosphate ions
C) chloride ions
D) urea
C
2. Which of these statements about the pharynx is true?
A) It extends from the nasal and oral cavities superiorly to the esophagus anteriorly.
B) The oropharynx is continuous superiorly with the nasopharynx.
C) The nasopharynx is involved in digestion.
D) The laryngopharynx is composed partially of cartilage.
B
3. Which structure is located where the esophagus penetrates the diaphragm?
A) esophageal hiatus
B) cardiac orifice
C) upper esophageal sphincter
D) lower esophageal sphincter
A
4. Which phase of deglutition involves contraction of the longitudinal muscle layer of the muscularis?
A) voluntary phase
B) buccal phase
C) pharyngeal phase
D) esophageal phase
D
1. The composition of saliva varies from gland to gland. Discuss how saliva produced by the parotid gland differs in action from saliva produced by the sublingual gland.
Parotid gland saliva is watery with little mucus but a lot of amylase, which allows it to mix freely with food during mastication and begin the digestion of carbohydrates. In contrast, sublingual gland saliva has a lot of mucus with the least amount of amylase of all the salivary glands. The high mucus content serves to lubricate the food for swallowing.
2. During a hockey game, the puck hits a player in the mouth, knocking out all eight of his most anterior teeth. Which teeth did the player lose and how does this loss affect food ingestion?
The incisors. Since these teeth are used for tearing off pieces of food during ingestion, the player will need to ingest foods that have already been cut into bite-sized pieces until the broken teeth are replaced.
3. What prevents swallowed food from entering the airways?
The laryngeal muscles constrict to prevent aspiration of food into the trachea. The larynx is pulled superiorly and the epiglottis covers the glottis (the opening to the larynx) blocking access to the trachea. Deglutition apnea (cessation of apnea) also takes place briefly.
4. Explain the mechanism responsible for gastroesophageal reflux.
If the lower esophageal sphincter does not close completely, the stomach’s acidic contents can back up into the esophagus, a phenomenon known as GERD.
5. Describe the three processes involved in the esophageal phase of deglutition.
Peristalsis moves the bolus down the esophagus and toward the stomach. Esophageal glands secrete mucus that lubricates the bolus and reduces friction. When the bolus nears the stomach, the lower esophageal sphincter relaxes, allowing the bolus to pass into the stomach.