Overview
The first lecture of the GI anatomy series sets out the whole gastrointestinal tract and the function of each of its parts, then concentrates on the oral cavity. It works outward from the boundaries of the cavity and its division into vestibule and oral cavity proper, through the palate and the muscles of the soft palate, the arches that form the exit into the oropharynx, the tongue with its intrinsic and extrinsic muscles, and finally the three paired salivary glands and where their ducts open.
The GI series and the parts of the tract
The lecture series covers, in order: oral cavity; pharynx and oesophagus; abdominal cavity, oesophagus and stomach; small intestine and large intestine; liver, gallbladder and pancreas; blood supply, lymphatics and nerve supply of the GI tract.
The tract itself is listed as:
- Oral cavity
- Pharynx, subdivided into oropharynx and laryngopharynx
- Oesophagus
- Stomach
- Small intestine
- Large intestine
- Rectum
- Anal canal
Function of each part
| Part | Function |
|---|---|
| Oral cavity | Initial breakup |
| Pharynx | Bypass the airway |
| Oesophagus | Convey to stomach |
| Stomach | Digestion, mechanical and acidic |
| Small intestine | Absorption of nutrients |
| Large intestine | Absorption of water |
| Rectum | Storage |
| Anal canal | Maintenance of continence |
Boundaries and relations of the oral cavity
The oral cavity is bounded by:
- Roof: hard palate anteriorly, soft palate posteriorly.
- Lateral wall: the cheek.
- Floor: the tongue and other soft tissues; specifically geniohyoid and mylohyoid, with the tongue above them.
- Anterior opening: the oral fissure.
- Exit: the oropharyngeal isthmus, bounded by the palatoglossal folds, leading into the oropharynx.
Continuities beyond the cavity: the nasal cavities communicate with the pharynx through the pharyngeal isthmus; below the pharynx the larynx leads on to the trachea, while the pharynx itself continues as the oesophagus.
Vestibule and oral cavity proper
The cavity is divided by the alveolar arches and teeth into two spaces.
Oral vestibule (outside the teeth):
- The slit between the cheek or lip and the teeth and gingiva. Buccinator lies in the wall of the cheek, so a bolus of food in the vestibule sits between buccinator and the teeth.
- Lined by buccal mucosa.
- The parotid duct opens into it, opposite the upper second molar.
Oral cavity proper (inside the alveolar arches):
- Contains the alveolar arches, teeth and gingivae, roofed by the palate and occupied by the tongue.
- The submandibular and sublingual ducts open into it.
- Visible in the floor of the mouth with the tongue elevated: the frenulum, the midline fold running from the undersurface of the tongue to the floor of the mouth, and the lingual gingiva on the tongue side of the lower teeth.
Gingiva is named by the surface it lies on: buccal gingiva on the cheek or vestibular side (synonyms given as vestibular gingiva and labial gingiva), and lingual gingiva on the tongue side.
Two of the clinical photographs used to demonstrate these spaces contain abnormalities that the slides do not label or name: nodular swellings on the upper alveolar and gingival area in the vestibule photograph, and a whitish object at the submandibular duct opening in the floor-of-mouth photograph [slides do not name either].
Case vignette
A case slide headed “Adam” lists only three abbreviations: RTC, ETOH and CHI [slide gives no expansion and does not elaborate].
The palate
The palate divides into a hard and a soft part:
- Hard palate: the anterior two-thirds. Formed by the maxilla anteriorly and the palatine bone posteriorly; the sphenoid is the third bone identified in this region on the basal view of the skull.
- Soft palate: the posterior third, ending at the midline uvula.
- Palatine rugae: the transverse ridges on the mucosa of the anterior hard palate.
Related bony features labelled on the inferior view of the skull: posterior nasal spine, incisive fossa with the incisive papilla overlying it, alveolar arch, posterior nasal aperture (choana), pyramidal process of the palatine bone, pterygoid hamulus, vomer, pterygoid fossa, greater wing of the sphenoid, pterygoid process with medial and lateral plates, opening of the pterygoid canal, greater and lesser palatine foramina, body of the sphenoid, styloid process and carotid canal.
Transcript flags (slides 12 and 13): on both palate figures the lecturer's callout boxes partly cover printed labels on the right of the figure, including one reading "Hard palate (mal..." and the "Lesser palatine foramen" label, so those cannot be read in full.
Muscles of the soft palate
- Tensor palati (tensor veli palatini): descends beside the pharyngotympanic tube, turns around the pterygoid hamulus and continues into the palatine aponeurosis.
- Levator palati (levator veli palatini): shown running into the soft palate.
- Palatine aponeurosis: the fibrous sheet of the soft palate, continuous with tensor palati and giving origin to palatoglossus from its underside.
- Palatopharyngeus: descends into the pharyngeal wall.
- Musculus uvulae: runs within the soft palate to the uvula, alongside levator veli palatini.
- Palatoglossus: arises from the underside of the palatine aponeurosis and passes into the tongue; the palatine tonsil lies just behind it.
Neighbouring structures shown in the same dissections: fibrous and cartilaginous parts of the pharyngotympanic tube, medial and lateral pterygoid plates, pterygopalatine fossa, nasal cavity and septum, the position of the palatopharyngeal sphincter, the pharyngeal raphe, buccinator, the pterygomandibular raphe and the superior constrictor of the pharynx.
Arches of the oropharynx
Looking into the open mouth, the uvula hangs in the midline and two mucosal folds run down the side wall of the opening:
- Palatoglossal arch: the anterior fold, with palatoglossus underlying it. These folds bound the oropharyngeal isthmus, the exit from the oral cavity proper.
- Palatopharyngeal arch: the posterior fold.
The tongue
Division and landmarks:
- Oral part: the anterior two-thirds.
- Pharyngeal part: the posterior one-third.
- The junction is marked by the V-shaped terminal sulcus, with the foramen cecum at its apex.
- The root of the tongue rests above mylohyoid and geniohyoid and is related to the hyoid bone and the mandible; the tongue also has an inferior surface facing the floor of the mouth.
Papillae shown on the dorsum: fungiform, filiform, foliate and vallate. The vallate papillae lie immediately in front of the terminal sulcus; the foliate papillae are labelled on the lateral part of the dorsum.
Muscles of the tongue
Extrinsic muscles (named as a bracketed group): palatoglossus, styloglossus, hyoglossus, genioglossus.
- Styloglossus runs from the styloid process into the tongue.
- Genioglossus arises from the mandible near the midline and fans into the tongue.
- Hyoglossus passes from the hyoid bone into the tongue.
- Mylohyoid and geniohyoid form the floor beneath the tongue.
Intrinsic muscles: superior longitudinal, vertical, transverse and inferior longitudinal fibre groups, separated in the midline by the lingual septum.
Salivary glands
Functions of saliva: cleaning, pH, amylase for starches, and lubrication. The glands are described by shape and by location, the three locations being parotid, submandibular and sublingual.
Parotid gland: lies in front of and below the external acoustic meatus, overlying the masseter posteriorly and bounded behind by sternocleidomastoid. Its duct runs forward across the masseter and pierces buccinator to open opposite the crown of the second upper molar tooth.
Submandibular gland: has deep and superficial parts. Its duct runs forward in the floor of the mouth in relation to the lingual nerve and hyoglossus, and opens at the sublingual caruncle beside the frenulum of the tongue.
Sublingual gland: lies in the floor of the mouth as a ridge, the sublingual fold, and drains by multiple small ducts that open along that fold.
Surface features of the floor of the mouth: frenulum of the tongue, fimbriated fold, deep lingual vein, sublingual fold overlying the sublingual gland, opening of the submandibular duct, and the sublingual caruncle.
Parasympathetic supply shown for the submandibular and sublingual glands: chorda tympani (from VII) joins the lingual nerve (from V3); preganglionic parasympathetic fibres reach the submandibular ganglion, and postganglionic fibres pass from the ganglion to the glands.
Self-test
- List the parts of the gastrointestinal tract in order from the oral cavity to the anal canal, including the subdivisions of the pharynx given.
- State the function attributed to each of: oral cavity, pharynx, oesophagus, stomach, small intestine, large intestine, rectum, anal canal.
- Describe the boundaries of the oral cavity: roof, lateral wall, floor, anterior opening and posterior exit.
- Distinguish the oral vestibule from the oral cavity proper.
- Describe where a bolus of food lies when it is in the vestibule, naming the muscle lateral to it.
- Distinguish buccal gingiva from lingual gingiva, and give the two synonyms for buccal gingiva.
- List the salivary duct openings found in each of the two oral spaces.
- Describe how the palate is divided into hard and soft parts, and name the bones forming the hard palate.
- Describe the palatine rugae and state where they lie.
- List the muscles of the soft palate identified in the lecture.
- Describe the course of tensor palati in relation to the pterygoid hamulus and the palatine aponeurosis.
- Explain the relationship between palatoglossus, the palatine aponeurosis and the palatoglossal arch.
- Distinguish the palatoglossal arch from the palatopharyngeal arch, and state where the palatine tonsil lies.
- Describe how the tongue is divided into oral and pharyngeal parts, naming the landmarks at the junction.
- List the papillae of the tongue shown and state which type lies immediately anterior to the terminal sulcus.
- Distinguish the intrinsic from the extrinsic muscles of the tongue, listing the members of each group.
- Describe the attachments of styloglossus, genioglossus and hyoglossus.
- List the functions of saliva given in the lecture.
- Describe the position of the parotid gland and the course of its duct to its opening.
- Describe where the submandibular duct runs and where it opens, and contrast this with the drainage of the sublingual gland.
- Trace the parasympathetic pathway shown to the submandibular and sublingual glands.
- A patient has an obstruction at a duct orifice sitting on a small papilla in the midline floor of the mouth, just lateral to the lingual frenulum. Which gland does this duct drain, and how would you confirm the location by inspection?
- A swelling is noticed in the cheek lining opposite the crown of the upper second molar. Which duct opening lies at that point, and which muscle does that duct pierce to reach it?
- Integrative: explain how the muscles of the soft palate determine the boundary between the oral cavity proper and the oropharynx.
Answers
Reveal answers
- Oral cavity; pharynx (oropharynx and laryngopharynx); oesophagus; stomach; small intestine; large intestine; rectum; anal canal.
- Oral cavity, initial breakup; pharynx, bypass the airway; oesophagus, convey to stomach; stomach, digestion that is mechanical and acidic; small intestine, absorption of nutrients; large intestine, absorption of water; rectum, storage; anal canal, maintenance of continence.
- Roof: hard palate anteriorly and soft palate posteriorly. Lateral wall: the cheek. Floor: the tongue and other soft tissues, with geniohyoid and mylohyoid beneath. Anterior opening: the oral fissure. Exit: the oropharyngeal isthmus, bounded by the palatoglossal folds, opening into the oropharynx.
- The vestibule is the slit outside the teeth, between the cheek or lip and the teeth and gingiva. The oral cavity proper is the space inside the alveolar and dental arches, roofed by the palate and containing the tongue.
- It lies in the vestibule between buccinator, which lies in the wall of the cheek, and the teeth.
- Buccal gingiva is the gingiva on the cheek or vestibular side, also called vestibular gingiva and labial gingiva. Lingual gingiva is the gingiva on the tongue side of the teeth.
- Vestibule: the parotid duct, opening opposite the upper second molar. Oral cavity proper: the submandibular and sublingual ducts.
- Hard palate is the anterior two-thirds, soft palate the posterior third ending in the uvula. The hard palate is formed by the maxilla anteriorly and the palatine bone posteriorly; the sphenoid is the third bone identified in this region of the skull base.
- Transverse ridges on the mucosa of the anterior part of the hard palate.
- Tensor palati (tensor veli palatini), levator palati (levator veli palatini), palatopharyngeus, musculus uvulae and palatoglossus, together with the palatine aponeurosis as the fibrous sheet of the soft palate.
- It descends beside the pharyngotympanic tube, turns around the pterygoid hamulus and continues into the palatine aponeurosis.
- Palatoglossus arises from the underside of the palatine aponeurosis and passes into the tongue; the mucosal palatoglossal arch is the fold overlying it.
- The palatoglossal arch is the anterior fold and the palatopharyngeal arch the posterior fold on the side wall of the oropharyngeal opening. The palatine tonsil lies just behind palatoglossus, that is between the two arches.
- Oral part, the anterior two-thirds; pharyngeal part, the posterior one-third. The junction is the V-shaped terminal sulcus, with the foramen cecum at its apex.
- Fungiform, filiform, foliate and vallate papillae. The vallate papillae lie immediately in front of the terminal sulcus.
- Intrinsic: superior longitudinal, vertical, transverse and inferior longitudinal fibre groups, separated by the midline septum, lying within the tongue. Extrinsic: palatoglossus, styloglossus, hyoglossus and genioglossus, which reach the tongue from outside it.
- Styloglossus runs from the styloid process into the tongue; genioglossus arises from the mandible near the midline and fans into the tongue; hyoglossus passes from the hyoid bone into the tongue.
- Cleaning, pH, amylase for starches, and lubrication.
- It lies in front of and below the external acoustic meatus, overlying masseter posteriorly and bounded behind by sternocleidomastoid. Its duct runs forward across masseter and pierces buccinator to open opposite the crown of the second upper molar.
- The submandibular duct runs forward in the floor of the mouth in relation to the lingual nerve and hyoglossus, and opens at the sublingual caruncle beside the frenulum of the tongue. The sublingual gland instead drains by multiple small ducts that open along the sublingual fold.
- Chorda tympani, from the facial nerve (VII), joins the lingual nerve (from V3); preganglionic parasympathetic fibres reach the submandibular ganglion, and postganglionic fibres pass from the ganglion to the submandibular and sublingual glands.
- The submandibular gland: its duct opens at the sublingual caruncle beside the frenulum of the tongue. Elevate the tongue and inspect the floor of the mouth, where the caruncle lies beside the frenulum with the sublingual fold running laterally from it.
- The parotid duct opening, which lies in the vestibule opposite the upper second molar; the duct pierces buccinator to reach it.
- The exit from the oral cavity proper is the oropharyngeal isthmus, bounded by the palatoglossal folds. Those folds are raised by palatoglossus, which takes origin from the underside of the palatine aponeurosis of the soft palate, so the soft palate and its muscles form the upper and lateral limits of the boundary, with the uvula, shaped by musculus uvulae, in the midline.