TheDigestiveSystemLecture1

Oral Cavity (Mouth)§ The mouth extends from the lips to

the oropharyngeal isthmus, through which it communicates with the oral part of the pharynx.

§ It is divided into an outer part, the vestibule and an inner part, the mouth proper.

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Vestibule§ Is A slit-like space.§ Bounded externally by the lips (anteriorly) and

the cheek (laterally); and internally by theupper and lower dental arches (gums andteeth).

§ When the mouth is closed, it communicatesposteriorly behind the third molar tooth withthe mouth proper.

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Oral part of pharynx

Oropharyngeal isthmus

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The Lips§ These are two folds that enclose the mouth

opening, and act as a voluntary sphincter.

§ Each lip is covered externally by skin and internally by mucous membrane that continues into the oral cavity, where it lines the mouth.

§ The core of the lip is filled by the fibers of the orbicularis oris muscle, loose connective tissue, labial vessels and nerves, lymphatic vessels, and several labial salivary glands. 4

§ Their ducts open into the vestibule.

§ The upper lip is marked at midline by a shallow vertical groove, the philtrum, which ends at the junction between skin and mucous membrane in a small prominence, the tubercle.

§ When the lips are closed, the fissure between them is called the oral fissure.

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Oral fissure

§ The internal surface of each lip is connected to the corresponding dental arch by a midline fold of mucous membrane, the labial frenulum.

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Labial Frenulum of upper lip

Labial Frenulum of lower lip 8

The Cheeks§ The cheeks form the lateral (outer)

walls of the vestibule.

§ The core of the cheek is principally formed by the buccinators muscle with a considerable amount of adipose tissue.

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§ The checks are lined by mucous membrane, and covered by skin.

§ Several small mucous secreting glands, the buccal glands are situated in the submucosa.

§ Four or five of these glands, the molar glands are larger than the rest, situated external to the buccinators around entry of parotid duct. Their ducts open into the mouth opposite 3rd molar teeth.

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Buccinator

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The Gingiva (Gum)§ The gengiva is a mucous membrane covers

the alveolar process of the maxillae and mandible, respectively, and is firmly adherents to their periosteum and to neck of the teeth.

§ They extend slightly into each socket to form the gingival sulcus.

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Gingiva

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The Teeth§ These are accessory organs fitted in

sockets of the alveolar process of the maxillae (upper or maxillary teeth) and mandible (lower or mandibular teeth).

§ Each tooth is composed of three principal regions, crown, neck, and root.

§ The crown is the portion of the tooth that lies above the level of the gum, and is the only visible part.

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§ Each tooth has from 1 – 3 roots, embedded in the corresponding socket of the alveolar process.

§ The neck is the constricted portion between the crown and roots, and situated close to the gum line.

§ The crown is covered by the hardest tissue in the body, the enamel.

§ The root is covered by cementum, which is a calcified tissue rather like bone.

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§ At the neck region, the enamel and cementum meet.

§ The tooth consists of dentin, a vascular calcified connective tissue that gives the tooth the basic shape and rigidity.

§ The dentin is perforated by minute canals, the dentinal tubules.

§ The dentin surrounds a cavity known as the pulp cavity.

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§ This cavity lies within the crown, and is filled by the dental pulp.

§ The dental pulp consists of a loose connective tissue in which nerves, and blood and lymphatic vessels are embedded.

§ The pulp cavity is enclosed with a simple columnar epithelium, which lies in contact with the inner surface of the dentine.

§ The cells of this columnar epithelium are termed odontoblasts.

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§ These cells present cytoplasmic extensions that occupy the dentinal tubules.

§ Throughout life, the odontoblast cells retain the power to produce dentin.

§ Inferiorly, the pulp cavity becomes continuous with a narrow canals run through the root(s), the root canals.

§ Each one of these canals has an apical foramen at its base, through which nerves, and blood and lymphatic vessels pass.

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§ In humans, there are two sets of teeth: The deciduous and permanent teeth.

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Deciduous TeethBegin to erupt about sixth months after birthBy the second year all teeth are eruptedIn Each JawIncisors: 4Canines: 2 10 X 2 = 20Molars: 4

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Permanent TeethBegin to erupt at the sixth yearThe third molar teeth are the last teeth begin toerupt after age year 17 up to 25 and sometimeeven to 30 year.In Each JawIncisors: 4Canines: 2 16 X 2 = 32Premolars: 4Molars: 6

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The Mouth Proper§ The mouth proper is bounded

anterolaterally by the upper and lower dental arches, and posteriorly by the oropharyngeal isthmus.

§ The roof is formed anteriorly by the hard palate and posteriorly by the anterior part of the soft palate.

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§ The floor is formed by the anterior two-thirds of the tongue, and by the reflection of the mucous membrane from the ventral (lower) surface and sides of the tongue to the internal surface of the gum.

§ The frenulum is a prominent median fold of mucous membrane connects the ventral surface of the tongue to the floor of the mouth.

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Oral part of pharynx

Oropharyngeal isthmus

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§ On either side of the frenulum of the tongue, the mucous membrane of the floor of the mouth presents an elevation, the sublingual fold, which is produced by the underlying sublingual gland.

§ The sublingual papilla is a small elevation situated on each side of the frenulum of the tongue.

§ It exhibits the opening of submandibular duct.

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§ The floor of the mouth is supported by the genioglossus, geniohyoid, mylohyoid, and anterior belly of digastrics muscles.

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Genioglossus

Geniohyoid

Mylohyoid 30

Tongue§ Is a muscular organ covered by a mucous

membrane, and is concerned, with the function of deglutition, taste, and speech.

§ Its anterior two-thirds lie in the mouth proper.

§ Its posterior one-third of is situated in the oral part of pharynx.

§ The root of the tongue is attached to the hyoid bone

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§ A fibrous septum divides the tongue into right and left half.

§ The mucous membrane covering dorsal surface of anterior two-thirds of tongue is roughened by three types of papillae, filiform, fungiform, and vallate (lingual papillae).

Filiform papillae § Are the smallest but the most numerous

papillae.

§ They are minute conical projections. 32

§ They are present throughout the dorsalsurface of the anterior two-thirds.

Fungiform papillae § Are larger and less numerous than the

preceding papillae.

§ They resemble mushroom and are visible as a bright red spots.

§ Although they are scattered throughout the dorsum of anterior two-thirds of tongue, but are especially numerous near sides and tip of the organ. 33

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Fungiform papilla

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Vallate papillae § Are the largest form.

§ They are circular-shaped, vary from 7 – 12 papillae arranged in the form of a V-shaped row with apex pointing backwards, immediately in front and parallel with the sulcus terminalis.

§ The latter marks the junction of the anterior two-third and the posterior third of tongue.

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§ The apex of the sulcus terminalis exhibits a small pit, the foramen cecum, which is the remains of the upper end of the thyroglossal duct.

§ The mucous membrane covering dorsalsurface of posterior third of tongue issmooth and has a nodular appearance dueto the presence of underlying mass ofmucous and serous glands andaggregations of lymphoid follicles, thelingual tonsil.

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Oral Part

Pharyngeal part

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Foramen caecum

Sulcus terminalis

Filiform papillae

Vallate papillae

Fungiform papillae

Palatine tonsilLingual tonsil

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§ A median fold, the median glossoepiglottic fold connects the tongue to the epiglottis.

§ On each side of this fold there is a deep fossa, the epiglottic vallicula, which is bounded laterally by the lateral glossoepiglottic fold.

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Median glossoepiglotic fold

Lateral glossoepiglotic

fold

Epiglottis

Epiglottic vallecula

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§ Each vallate papilla is surrounded by a deep circular sulcus containing numerous taste buds and serous glands.

§ These glands secrete a lipase which perhaps prevents the formation of a hydrophobic layer over the taste buds that would prevent their function.

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§ The fungiform and vallate papillae present taste buds on their surfaces.

§ These buds are specialized onion-shaped structures containing 50 – 100 epithelial cells, most of which are known as the taste cells.

§ These cells are detectors of tastants (substances capable of eliciting taste).

§ The bud rests on the basal lamina. 43

§ At the apical portion of the buds, the taste cells present microvilli that project through an openings termed the taste pores.

§ Other cells have a supportive function, secreting an amorphous material that surrounds the microvilli in the taste pore.

§ Basal cells are responsible for the replacement of all cell types.

§ In the human there are at least four types of taste perception, saltiness, sourness, sweetness, and bitterness.

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§ Tastants dissolved in saliva contact the taste cells through the taste pore, interacting with taste receptors (sweet and bitter taste) or ion channels (salty and sour taste) on the surface of the cells.

§ The result is a depolarization of the taste cells, leading to the release of neurotransmitters that will, in turn, stimulate afferent nerve fibers connected to the taste cells.

§ This information will be processed by central gustatory neurons. 45

Taste buds

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Vallate papillaTaste buds

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§ The mucous membrane covering inferior surface of tongue is smooth, and thin.

§ It presents scattered mucous and serous glands near sides and tip of the organ.

§ Behind the tip, there is a large mixed gland, the anterior lingual gland.

§ In the median plane, the frenulum of the tongue connects the inferior surface to floor of mouth cavity.

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Inferior surface of

tongue

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Muscles of the Tonguea. Genioglossus: § Fan-shaped, forms the main mass of

tongue.

§ Arises from the superior mental spine (upper genial tubercle) of the mandible.

§ Inserted into mucous membrane covering the dorsal surface of tongue (from the tip to the base), and the body of hyoid bone.

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Actions: § The posterior fibers protrude the tongue.

§ The middle fibers depress central part of tongue to enlarge mouth cavity.

§ The anterior fibers depress and retract tip of tongue.

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Genioglossus

Geniohyoid

Mylohyoid 52

b. Hyoglossus: § Arises from lateral part of body and greater

wing of hyoid bone.

§ Inserted in to posterior half of side of tongue.

Action: Depresses side of tongue, and assists the genioglossus in the enlargement of the oral cavity.

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Hyoglossus

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c. Styloglossus: § Arises from anterior aspect of lower part of

styloid process and upper part of stylohyoid ligament.

§ Inserted into whole length of side of tongue.

Action: Pulls tongue upwards and backwards.

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Styloglossus

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d. Palatoglossus:§ Arises from inferior surface of palatine

aponeurosis.

§ It descends in front of palatine tonsil, raises a fold of mucous membrane, the palatoglossal fold or arch (anterior pillar of fauces).

§ Inserted into side of tongue.57

Action Acts as sphincter at oropharyngeal isthmus, elevates the root of the tongue and narrows the transverse diameter of the isthmus by approximating the palatoglossal arches.

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Palatoglossus

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Sensory Supply of TongueA.§ The mucous membrane covering anterior

two-thirds of tongue is supplied by lingual branch of the mandibular nerve.

§ The trigeminal component of this nerve mediates common sensibility.

§ The chorda tympani component mediates taste.

B. § The posterior third of tongue is supplied by

glossopharyngeal nerve. 60

Motor Supply of Tongue

§ The palatoglossal muscle is supplied by pharyngeal plexus of nerves.

§ The remaining muscles (intrinsic and extrinsic are innervated by hypoglossal nerve.

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Blood Supply of the Tongue1.Lingual artery – Branch of external carotid

artery2.Tonsilar artery: Branch of facial artery.3. Ascending pharyngeal artery – Branch of

external pharyngeal artery.

Lymph Drainage1. Sides of anterior 2/3 - Submandibular & Deep

cervical lymph nodes.2. Tip of tongue – Submental lymph nodes.3. Posterior 1/3 – Deep cervical lymph nodes. 62

Sensory Innervation of the Mouth1.Roof: Greater palatine & Nasopalatine nerves

– Branches of Maxillary nerve.2.Floor: Lingual nerve – Branch of mandibular

nerve.Taste sensation mediated by chorda tympani –Branch of facial nerve.

3. Cheek: Buccal nerve – Branch of mandibular nerve.

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§ The mucous membrane of the mouth proper is composed of stratified squamous epithelium keratinized or nonkeratinized and lamina propria.

§ Keratinized squamous epithelium covers the hard palate and dorsal surface of anterior two-thirds of tongue.

§ The remaining part of the epithelial lining (soft palate, floor of the mouth, and the dorsal surface of the posterior third and the inferior surface of the tongue) is of the nonkeratinized type. 64