Digest 1 Checklist
Oral Cavity to the Stomach
Digestive system The digestive system consists of the digestive tract and
accessory digestive organs. The digestive tract is also called
the gastrointestinal (GI) tract.
The digestive tract is about 30 feet long and it passes through
the body (a tube within a tube). Consequently, material
within the digestive tract is not inside the body.
Digestive tract The digestive tract is the site of the mechanical and chemical
breakdown of food, the absorption of food, and the
elimination of wastes. It consists of the following parts:
Small intestine (duodenum, jejunum, ileum)
Cecum and appendix
Colon (ascending, transverse, descending and sigmoid)
Rectum and anal canal
Accessory digestive organs Accessory digestive organs secrete or store chemicals that
function in the breakdown and absorption of food, and
chemicals that are waste products. The accessory digestive
organs are the salivary glands, liver, gallbladder, and
Oral cavity (mouth) The oral cavity is the part of the digestive tract bounded by
the lips, cheeks, palate, and throat. The tongue occupies the
oral cavity and forms part of its floor.
The oral cavity is the beginning of the digestive system and it
functions to receive food and liquids. Within the oral cavity
the process of mechanical and chemical digestion begins.
Vestibule The vestibule is the part of the oral cavity between the lips or
cheeks and the alveolar processes. People who want to
develop oral cancer place smokeless tobacco in the vestibule.
Teeth The teeth are bonelike structures embedded in the jaws
(mandible and maxillae). The exposed surfaces of the teeth
are covered with hard enamel.
The teeth mechanically breakup food, which is important to
the digestive process for two reasons:
It increases the surface area of the food because many small
pieces of food have a larger surface area than one large piece.
With increased surface area, digestive enzymes can more
easily reach food molecules and break them down.
It breaks apart plant cells, which have an outer cell wall of
cellulose. Human digestive enzymes cannot break down
cellulose, so the only way for us to digest plants is to first
mechanically break open the plant cells.
Mastication Mastication is the process of chewing food. The food is
mechanically broken down and mixed with saliva to form a
single mass, called a bolus, which can be swallowed.
Muscles of mastication The muscles of mastication provide the force to move the
mandible. The muscles of mastication are the masseter,
temporalis, and pterygoid muscles.
Masseter muscle The masseter elevates the mandible, providing the force to
Temporalis muscle The temporalis muscle elevates the mandible.
Pterygoid muscles The lateral and medial pterygoid muscles move the mandible
from side-to-side, producing a shearing effect that helps to
Buccinator The buccinator muscle compresses the cheek, helping to hold
food between the teeth during mastication.
Tongue The tongue consists of skeletal muscles called the intrinsic
tongue muscles. These muscles enable the tongue to change
The extrinsic tongue muscles attach to the tongue and move it
The tongue pushes and holds food between the teeth, mixes
food with saliva to form a bolus of food, pushes the bolus
into the throat during swallowing, and contains taste buds
that enable us to analyze food.
Lingual tonsil The lingual tonsil is a collection of lymphatic tissue on the
posterior surface of the tongue. It helps to protect against
Tongue blood vessels There are many superficial blood vessels under the tongue,
making this location ideal for administering certain
medications. For example, nitroglycerin is used to treat
angina, which is chest pains caused by inadequate blood
delivery to the heart.
Although absorption of materials normally takes place
further along the digestive tract, it is possible for some
substances to be absorbed in the oral cavity.
Salivary glands There are three major pairs of salivary glands: the parotid,
submandibular, and sublingual salivary glands. Many
smaller (microscopic) salivary glands are scattered
throughout the cheeks, tongue, and palate.
Saliva Salivary glands produce a secretion called saliva. Although
saliva is continuously produced, its production increases
Functions of saliva Saliva contains amylase, a digestive enzyme that starts the
digestion of starches.
Mucus (mucin) in saliva acts as a lubricant, protecting the
lining of the digestive tract and making it easier to swallow
Substances in the food dissolve in saliva. Once in solution,
these substances can activate taste receptors in the tongue.
Saliva washes away bacteria and contains lysozyme, an
enzyme that kills some bacteria. Decreased saliva production
(xerostomia) results in increased tooth decay and infections
of the gums.
Parotid gland The parotid glands are the largest salivary glands. They are
located under the skin just anterior to the ear.
The parotid duct from the parotid gland passes through the
fat and muscle of the cheek to open next to the second upper
A detached part of the parotid gland, called the accessory
parotid gland, is located along the parotid duct.
When the parotid glands are infected by the mumps virus,
they swell and become painful.
Submandibular gland The submandibular gland is located under the mandible. It is
about half the size of the parotid gland.
The submandibular duct extends to the middle of the oral
cavity under the tongue.
Sublingual gland. The sublingual gland is located under the tongue.
The sublingual gland has 8 - 20 small ducts (not shown) that
open onto the floor of the oral cavity.
Digestion in the oral cavity The teeth mechanically break up food.
The muscles of mastication move the mandible during
chewing. The masseter and temporalis powerfully elevate the
mandible, providing the force to crush food between the
teeth. The pterygoid muscles move the mandible from side-
to-side, producing a shearing effect that helps to break up
The buccinator and tongue muscles help to hold the food
between the teeth. In addition, the tongue mixes the food
with saliva to form a bolus of food that can be swallowed.
The salivary glands produce saliva, containing the digestive
enzyme amylase, which starts the process of starch digestion
in the mouth.
Palate The nasal cavity is separated from the oral cavity by the
palate, which has two parts.
Hard palate The hard palate is bone covered by a mucous membrane.
Soft palate The soft palate is muscle and mucous glands covered by a
mucous membrane. The part of the soft palate hanging down
at the entry into the throat is called the uvula.
Vibrations of the relaxed soft palate during sleep can produce
snoring sounds. Surgical removal of part of the soft palate is
sometimes used to prevent snoring.
Functions of the palate By separating the nasal and oral cavities, the palate allows us
to chew food and breathe at the same time.
During swallowing, the soft palate can close the passageway
from the throat to the nasal cavity, preventing materials from
entering the nasal cavity.
Palatine tonsil One of two masses of lymphatic tissue in the oral cavity that
help to protect against infections. Each palatine tonsil is
located in the superior, lateral, posterior part of the oral
Pharynx (throat) The pharynx is a common passageway for the digestive and
respiratory systems. Foods and liquids from the oral cavity
pass through the pharynx. Air from the nasal or oral cavities
passes into the pharynx during inspiration and out of the
pharynx during expiration.
The pharynx is subdivided into the nasopharynx,
oropharynx, and laryngopharynx.
Nasopharynx The nasopharynx is superior to the soft palate and it connects
the nasal cavity and the oropharynx.
Oropharynx The oropharynx (red) is posterior to the oral cavity, inferior
to the soft palate, and superior to the larynx (see next slide).
The oropharynx connects the nasopharynx and the oral
cavity to the laryngopharynx.
Larynx (voice box) The larynx is the beginning of the lower respiratory tract.
The larynx consists of nine pieces of cartilage, laryngeal
skeletal muscles, and the vocal cords.
The larynx is located inferior to the hyoid bone and anterior
to the laryngopharynx.
Laryngopharynx The laryngopharynx is posterior to the larynx. It extends to
the inferior border of the larynx and cervical vertebra C6
The laryngopharynx connects to the larynx, for the passage
of air, and to the esophagus. The esophagus is a tube that
moves ingested materials to the stomach (more later in this
Pharyngeal constrictors The wall of the pharynx consists of skeletal muscles.
When swallowing food or liquids, the pharyngeal muscles
constrict and push the ingested materials inferiorly into a
tube called the esophagus (red), which connects the throat
The superior pharyngeal constrictor contracts first, followed
by the middle pharyngeal constrictor and then the inferior
Functions of the larynx Laryngeal cartilages form a passageway for air flow. During
inspiration, air passes through the nasal cavity or oral cavity,
enters the oropharynx, goes into the larynx, and flows on
through to the lungs. During expiration, air flows in the
Air passing through the larynx vibrates the vocal cords in the
larynx, resulting in sound production.
During swallowing, laryngeal muscles close the opening into
the larynx, preventing swallowed materials from entering the
Thyroid cartilage The thyroid cartilage is the largest and most prominent
laryngeal cartilage. It forms a protrusion of the throat called
the "Adam's apple."
During swallowing, muscles attached to the thyroid cartilage
and other parts of the larynx pull the larynx superiorly and
anteriorly. This allows the pharynx to expand and moves the
laryngeal opening out of the way of swallowed materials.
Epiglottis The epiglottis is a laryngeal cartilage located at the opening
into the larynx.
During swallowing, the larynx moves superiorly and
anteriorly. Upward movement of the epiglottis is prevented,
however, by the base of the tongue. As a result, the epiglottis
folds over the opening of the larynx. In addition, as solid
swallowed materials slide over the epiglottis, they push on it,
helping to fold it over the laryngeal opening.
Analogy: The epiglottis is like the lid on a toilet seat. When
the lid is down, nothing goes into the toilet (larynx).
In humans, the epiglottis is not essential for swallowing. The
laryngeal muscles can prevent materials from entering the
larynx, and even if the epiglottis is destroyed by disease,
swallowing still occurs.
Trachea, or windpipe The trachea is a tube with "rings" of cartilage that hold it
open. The trachea is located inferior to the larynx and
anterior to the esophagus (red).
The trachea transports air toward and away from the lungs.
Events of swallowing The tongue pushes the bolus of food into the pharynx.
The soft palate closes the entry into the nasal cavity.
The pharyngeal constrictors push the food through the
pharynx into the esophagus.
Skeletal muscles move the larynx superiorly and anteriorly,
allowing greater expansion of the pharynx and moving the
laryngeal opening out of the way of swallowed materials.
Laryngeal skeletal muscles close the opening into the larynx,
helping to prevent the entry of swallowed materials into the
The epiglottis folds over the laryngeal opening, helping to
prevent the entry of swallowed materials into the larynx.
Esophagus The esophagus, which is 25 cm (10 in) long smooth muscle
tube, connects the laryngopharynx to the stomach by passing
through the thoracic cavity to the abdominal cavity.
Contraction of smooth muscle in the wall of the esophagus
moves swallowed materials through the esophagus.
Esophageal sphincters Esophageal sphincters regulate the movement of materials
into and out of the esophagus. The upper esophageal
sphincter is skeletal muscle around the superior end of the
esophagus. The lower esophageal sphincter is smooth
muscle that is part of the wall of the lower end of the
When not swallowing, the upper esophageal sphincter
prevents air from entering the esophagus and the lower
esophageal sphincter prevents the movement of stomach
contents into the esophagus. During swallowing, relaxation
of the sphincters allows materials to enter the esophagus and
pass through to the stomach.
Achalasia is difficult in swallowing that can occur if the lower
esophageal sphincter does not relax properly.
Descending aorta The descending aorta lies next to the esophagus. The
descending aorta is the major blood vessel carrying blood
from the heart to the lower body.
Diaphragm The diaphragm is a skeletal muscle partition that separates
the thoracic and abdominal cavities. Note that the esophagus
and aorta pass through the diaphragm.
Contraction of the diaphragm during inspiration increases
1. A man is observed to have the following symptoms. He can chew, speak, and swallow
normally. When he chews, however, there is a tendency for food to drool out of the right side
of his mouth. Given that the problem results from nerve damage, explain these observations.
2. A woman experiences pain in her right cheek when eating. At other times, there is no
discomfort. A radiograph reveals small calcium deposits called calculi (meaning pebbles) in the
superficial soft tissue of her cheek. How could calculi cause pain in this location when eating?
3. General anesthesia for surgical procedures causes unconsciousness, unresponsiveness to
painful stimuli, and skeletal muscle relaxation. It can also cause postoperative nausea and
vomiting. When scheduled for surgery the next day, no solid foods are eaten after the evening
meal and no liquids are ingested after midnight. Explain why this makes sense.
4. If you laugh while trying to drink, sometimes liquid will shoot out your nose. Explain what
5. Is it possible to swallow while upside down and have the swallowed material end up in the
6. Heart burn results from damage to the esophagus by the reflux of stomach acid into the
esophagus. What is one possible explanation for how this could happen?
1. Because he can chew, speak, and swallow normally, it is likely that the nerves supplying the
muscles of mastication, the tongue, and the larynx are not damaged. The nerve (facial)
supplying the right buccinator muscle is damaged. As a result of the paralysis of this muscle,
food is not held between the teeth and cheek and tends to drool out of the corner of the mouth.
Sometimes, dental anesthesia can temporarily affect the cheek, lips, and tongue muscles.
2. The calculi are calcium deposits from saliva that can block the ducts that release saliva from the
salivary glands. If the saliva cannot escape and builds up, the swelling can cause pain. Often
the pain is first felt when eating because this is when saliva production increases.
3. If vomiting occurs when skeletal muscles are relaxed or not as responsive as usual, the normal
mechanisms that prevent materials from going into the respiratory tract might not respond to the
vomit. Thus, it is possible that the vomit could enter the respiratory tract and block air flow.
Vomit can also introduce bacteria into the respiratory tract and cause infections. Before surgery
food and liquids are restricted to reduce the volume of any potential vomit. Time is allowed for
food to be digested and eliminated from the stomach. Liquids are restricted, but not for so long
that dehydration occurs before the surgery.
4. Normally, the superior movement of the soft palate during swallowing prevents materials from
entering the nasal cavity. Sometimes, when trying to swallow and laugh, the conflicting signals
sent to the soft palate muscles results in their relaxation when they should be contracting.
Diphtheria is a rare bacterial infection because it is prevented by a vaccine. If infection does
occur, however, the bacteria produces a toxin that can destroy nerve cells, including those
supplying the soft palate muscle. The result can be the movement of swallowed material out the
5. It is possible to swallow while upside down. The pharyngeal constrictors push the bolus into
the esophagus and contraction of the esophagus pushes the bolus into the stomach. Although
gravity can assist this movement, it is not necessary. The muscle action can even move the
bolus against gravity when a person is upside down.
Another example of this contraction process occurs in astronauts. Even when they are in a
weightless environment, they are able to swallow and move food into the stomach.
6. Failure of the lower esophageal sphincter to stay closed can result in acid reflux into the