Digest 1 Checklist Oral Cavity to the Stomach by rux99038

VIEWS: 4 PAGES: 9

									                                 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:

                              Oral cavity
                              Pharynx
                              Esophagus
                              Stomach
                              Small intestine (duodenum, jejunum, ileum)
                              Duodenum
                              Jejunum
                              Ileum
                              Large intestine
                                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
                              pancreas.

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.




                                         1
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
                         crush food.

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
                         breakup food.

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
                         shape.

                         The extrinsic tongue muscles attach to the tongue and move it
                         about.

                         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
                         infections.




                                    2
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
                       when eating.

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
                       food.

                       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
                       molar tooth.

                       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.




                                  3
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
                               food.

                               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
                               cavity.




                                          4
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
                          (gold).

                          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
                          lesson).

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
                          and stomach.

                          The superior pharyngeal constrictor contracts first, followed
                          by the middle pharyngeal constrictor and then the inferior
                          pharyngeal constrictor.




                                     5
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
                          reverse direction.

                          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
                          larynx.

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.




                                     6
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
                        larynx.

                        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
                        esophagus.

                        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
                        thoracic volume.




                                   7
                                      Application Questions

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
   goes wrong.

5. Is it possible to swallow while upside down and have the swallowed material end up in the
   stomach?

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?




                                                 8
                                        Application Answers

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
   nose.

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
   esophagus.




                                                  9

								
To top