• Formed by the cheeks, hard and soft palates, lips, and tongue

• The vestibule: Space bounded externally by the cheeks and lips and internally by the teeth and gums

• The tongue:

– Together with its associated muscles, forms the floor of the oral cavity

– Composed of skeletal muscle covered with mucous membrane

Salivary Glands

• Secretes saliva

• Outside the mouth and pour their contents into ducts that empty into the oral cavity

• 3 pairs of major salivary glands:

– Parotid

– Submandibular

– Sublingual glands

• Saliva lubricates food and starts the chemical digestion of carbohydrates

Small Salivary Glands

• The mucous membrane of the mouth and tongue contains many small salivary glands

• Open directly or indirectly via short ducts to the oral cavity

• Make a small contribution to saliva

• These glands include:

– Labial glands - in lips

– Buccal glands– in cheeks

– Palatal glands – in palate

– Lingual glands - in the tongue

Composition of Saliva

• Chemically, saliva is 99.5% water and 0.5% solutes

• Solutes:

– Ions including sodium, potassium, chloride, bicarbonate & phosphate

• Dissolved gases and various organic substances

– Urea

– Uric acid

– Mucus

– Immunoglobulin A

• Bacteriolytic enzyme - lysozyme

• Salivary amylase - digestive enzyme that acts on starch

Functions of Saliva

• Water in saliva: Provides a medium for dissolving food

• Chloride ions: Activate salivary amylase

• Bicarbonate and phosphate ions: Buffer acidic foods that enter the mouth

• Mucus: Lubricates food

• Immunoglobulin A (IgA) - Prevents attachment of microbes

• Lysozyme - Kills bacteria


• Control: By the autonomic nervous system

• Amounts of saliva - 1000–1500 mL

• Parasympathetic stimulation

– Promotes continuous secretion of a moderate amount of saliva

• Sympathetic stimulation

– Dominates during stress, resulting in dryness of the mouth


• Accessory digestive organ

• Composed of skeletal muscle covered with mucous membrane

• Divided into symmetrical lateral halves by a median septum that extends its entire length

• Attached inferiorly to the hyoid bone, styloid process of the temporal bone, and mandible

• Each half of the tongue consists of an identical complement of extrinsic and intrinsic muscles

The Extrinsic Muscles of the Tongue 

• Hyoglossus

• Genioglossus

• Styloglossus

• Originate outside the tongue (attach to bones in the area)

• Insert into connective tissues in the tongue

• Functions:

– Move the tongue from side to side and in and out to maneuver food for chewing

– Shape the food into a rounded mass

– Force the food to the back of the mouth for swallowing.

– Also form the floor of the mouth and hold the tongue in position

• Originate in and insert into connective tissue within the tongue

• They alter the shape and size of the tongue for speech and swallowing

• The intrinsic muscles include:

– Longitudinalis superior

– Longitudinalis inferior

– Transversus linguae

– Verticalis linguae muscles

The Teeth (Dentes)

• Accessory digestive organ

• Located in sockets of the alveolar processes of the mandible and maxillae

• The alveolar processes are covered by the gingivae (gums)

• Sockets are lined by the periodontal ligament or membrane

• A typical tooth has 3 major external regions:

– Crown

– Root

– Neck

• The crown

– Visible portion above the level of the gums

– Embedded in the socket

• The neck

– Constricted junction of the crown and root near the gum line

– Internally, dentin forms the majority of the tooth

• Dentin

– Consists of a calcified connective tissue

– Gives the tooth its basic shape and rigidity

– Harder than bone (higher content of calcium salts)

• Enamel

– The dentin of the crown is covered by enamel

– Consists of calcium phosphate and calcium carbonate

– Enamel is the hardest substance in the body

– Serves to protect the tooth from the wear and tear of chewing

– Protects against acids that can easily dissolve dentin

• Cementum

– The dentin of the root is covered by cementum

– Another bonelike substance - attaches the root to the periodontal ligament

• The Pulp Cavity

– Lies within the crown and is filled with pulp

– Pulp - A connective tissue containing blood vessels, nerves & lymphatic vessels

• Root Canals

– Narrow extensions of the pulp cavity

– Run through the root of the tooth

– Each root canal has an opening at its base, the apical foramen

– The blood vessels bring nourishment, the lymphatic vessels offer protection, and the nerves provide sensation

There are two dentitions:

• Deciduous

• Permanent

Mechanical Digestion in the Mouth

• Mechanical digestion results from chewing or mastication

• Food is manipulated by the tongue

• Ground by the teeth

• Mixed with saliva

• Reduced to a soft, flexible, easily swallowed mass - Bolus

• Food molecules begin to dissolve in the water of saliva

Chemical Digestion in the Mouth

• Ingested disaccharides and starches must be broken down into monosaccharides - For absorption

Salivary amylase:

• Begin starch digestion by breaking down starch into smaller molecules such as:

– The disaccharide maltose

– The trisaccharide maltotriose

– Short-chain glucose polymers called -dextrins

• Salivary amylase in the swallowed food continues to act on the starches for about another hour

• Later, stomach acids inactivate it

Lingual lipase

• Secreted by lingual glands in the tongue

• Becomes activated in the acidic environment of the stomach

• Thus starts to work after food is swallowed

• Breaks down dietary triglycerides into:

– Fatty acids

– Diglycerides


• Funnel-shaped tube

• Composed of skeletal muscle and lined by mucous membrane

• Divided into three parts:

– Nasopharynx - Functions only in respiration

– Oropharynx & Laryngopharynx – digestive as well as respiratory functions

• Swallowed food passes from the mouth into the oropharynx and laryngopharynx

• The muscular contractions help propel food into the esophagus

The Esophagus

• Collapsible muscular tube - 25 cm long

• Lies posterior to the trachea

• Begins at the inferior end of the laryngopharynx

• Passes through the mediastinum anterior to the vertebral column

• Pierces the diaphragm through an opening called the esophageal hiatus

• Ends in the superior portion of the stomach


• Secretes mucus and transports food into the stomach

• Does not produce digestive enzymes

• Does not carry on absorption

Esophageal Sphincter

• The Upper Esophageal Sphincter

– Consists of skeletal muscle

– Regulates the movement of food from the pharynx into the esophagus

• The Lower Esophageal Sphincter

– Consists of smooth muscle

– Regulates the movement of food from the esophagus into the stomach


• The movement of food from the mouth into the stomach

• Facilitated by the secretion of saliva and mucus

• Involves the mouth, pharynx, and esophagus

• Occurs in three stages

• The Voluntary stage - Bolus is passed into the oropharynx

• The Pharyngeal stage (involuntary passage) - through the pharynx into the esophagus

• The Esophageal stage (involuntary passage) - through the esophagus into the stomach

The Pharyngeal Stage

During the pharyngeal stage of deglutition the tongue rises against the palate, the nasopharynx is closed off, the larynx rises, the epiglottis seals off the larynx, and the bolus is passed into the esophagus

During the esophageal stage of deglutition food moves through the esophagus into the stomach via peristalsis

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