Tongue Anatomy and Function

Tongue Structure

• Composed of skeletal muscle
• Consists of a root, body, and apex
• Curved dorsal surface and inferior surface
• The oral part is mobile; the root is attached to the floor of the pharynx
• Sulcus terminalis is a V-shape groove on the dorsum between the anterior and posterior parts
• Covered by mucosa which is rough on the dorsal surface but thin on the inferior surface

Tongue Mucous Membrane

• Contains lingual papillae
• Anterior 2/3 contains
• Filiform papillae that are conical, keratinized, and sensitive to touch
• Fungiform papillae scattered near the apex and margins, with 5 taste bud
• Circumvallate papillae are large, with taste buds for salty, sweet, bitter, and sour sensations
• Foliate with taste buds for salty, sweet, bitter, and sour sensations
• Posterior 1/3
• Has no lingual papillae
• Contains lymphoid nodules (lingual tonsil)

Tongue Nerve Supply

• Motor nerves
• Vagus nerve (CN X) innervates the palatoglossus muscle
• Hypoglossus nerve (CN XII) innervates extrinsic and intrinsic muscles
• Sensory nerves
• Trigeminal nerve CN V (mandibular division lingual branch) provides general sensation to the anterior 2/3
• Facial nerve CN VII (chorda tympani branch) provides special sensation (taste) to the anterior 2/3
• Glossopharyngeal nerve CN IX + CN X provides sensation to the posterior 1/3

Tongue Function

• Mastication (chewing)
• Taste
• Swallowing
• Speech
• Oral cleansing
• Movement, shape, and position are controlled by muscles
• Intrinsic muscles permit changes in shape (CN XII)
• Extrinsic muscles (originate from the mandible and hyoid bone) alter the position and movements (side to side, retraction & protrusion) (CN XII)

Clinical Correlates of the Tongue

• Touching the posterior part elicits the gag reflex, which is stimulated by CNX and CNIX, leading to muscular contractions of the pharynx
• Genioglossus Paralysis results in the tongue shifting posteriorly, obstructing the airway and risking suffocation
• During general anesthesia, muscle relaxation can cause airway obstruction, necessitating the insertion of an airway
• Allows quick absorption of drugs into the deep lingual veins
• Lingual carcinoma can metastasize along the IJVs into the neck

Types of Salivary Glands

• Major salivary glands: parotid, submandibular, and sublingual
• Minor salivary glands: located on the palate, lips, cheeks, and tongue
• Saliva contains water, mucus, inorganic ions, and organic substances (enzymes and antibodies)

Functions of Saliva

• Moistens the mucous membrane of the oral cavity which facilitates chewing, speech and swallowing
• Prevents tooth decay
• Aids in digestion of carbohydrates via amylase enzyme, lipase
• Mouthwash
• Facilitates taste sensation
• Provides antimicrobial functions via lysozyme, IgA

Types of Salivary Acinus & Saliva

• Parotid glands
• mainly serous
• contain high content of amylase
• Sublingual glands
• mostly mucus -contain mucins
• Submandibular glands
• serous/mucus
• contain weak amylase and lysozyme

Saliva Secretion

• Acinar cells secrete isotonic primary saliva
• As primary saliva passes through ducts, Na+ and Cl- are reabsorbed, and K+ and HCO3¯ are secreted into the lumen which makes saliva becomes hypotonic and alkaline (secondary saliva) before excretion into the mouth
• At a high flow rate there is no time for Na+ and Cl- reabsorption, the composition of secondary saliva becomes similar to that of primary saliva
• Stimulated saliva (serous secretion increase) becomes more alkaline due to elevated HCO3 content

Regulation of Saliva Secretion

• The parasympathetic stimulation (by taste, smell, touch, mastication of food, nausea)
• Parasympathetic stimulation increases serous secretion (parotid, submandibular) rich in water, amylase, K+ and HCO3
• Sympathetic stimulation increases mucin secretion (sublingual, submandibular), saliva comes thick and viscous
• Increases reabsorption of Na+ and Cl- from the lumen of salivary ducts into the blood and increases secretion of K+ into the duct lumen

Salivary Gland Nerve Supply

• Parotid Gland
• Parasympathetic supply via the cranial nerve IX (glossopharyngeal nerve)
• Sympathetic supply via the sympathetic chain, but influence is minimal
• Submandibular and Sublingual Glands
• Parasympathetic supply via the facial nerve (cranial nerve VII)
• Sympathetic supply same as parotid

Salivary Gland Clinical Correlation

• Sialography includes radiographic examination of major ducts & secretory units of the parotid & submandibular gland by injection of contrast medium, to show blockage of main ducts by calculi (stones), and tumors
• Majority of salivary gland have tumors occurring in the parotid gland, which are benign; parotidectomy presents surgical challenges because the facial nerve & its branches are embedded in the gland
• Mumps is a viral infection of the parotid gland, causes inflammation (parotiditis); parotid gland capsule & cervical fascia limit swelling and thus increase pressure in the gland, causes severe pain and tenderness

Structure of the Esophagus

• 25 cm long, extending from the pharynx to stomach
• Upper part contains striated muscle fibers, middle part contains striated and smooth muscle, and lower part contains smooth muscle
• Composed of three regional locations: cervical, thoracic, and abdominal
• Is lined with mucous glands to secrete mucous which prevent epithelial excoriation by food entering, and protects the esophageal wall from digestion by gastric juices if reflux from the stomach occurs
• Conducts food from the pharynx to stomach

Blood Supply to the Esophagus

• Three arterial sources
• Cervical part supplied by the inferior thyroid A branching from the subclavian A
• Thorax region: supplied by the aorta via esophogeal branches
• Abdomen region is supplied by the left gastric artery
• Venous drainage
• Drained by the inferior thyroid, and Azygos veins
• Left gastric vein drains into the portal system

Processes during Swallowing

• Consists of three phases
• Oral phase (voluntary): the apex of the tongue starts to raise against the hard palate to propel the food bolus upward and backward, towards the pharynx
  • This stage lasts about one second
• Pharyngeal phase (involuntary)
• Food bolus stimulates swallowing receptors around the opening of the pharynx
• Impulses (sensory stimuli) passes via the Trigeminal CN 5 & Glossopharyngeal CN 9 to the swallowing center in the medulla oblongata & pons (brain stem) to initiate a series of automatic muscles contraction
• Efferent impulses (motor) return via the CN 5, 9, 10, 12 cranial Ns
• The soft palate and uvula is pulled upward to seal off the nasal cavity
• Palatopharyngeal folds approximated to each others allowing food bolus to pass
• The larynx is raised and epiglottis is Seal over the glottis - This movement of the larynx assists the upper esophageal sphincter to relax and allows food to move easily into the upper esophagus
• Upper esophageal sphincter closes to prevent food regurgitation to the pharynx
• Esophageal phase (involuntary)
• Primary esophageal peristalsis: It is a wave-like contraction that begins in the pharynx and spreads down to the esophagus to propel the food bolus downward
• The lower esophageal sphincter relaxes several seconds before the waves of peristalsis approaches to it, allowing the bolus to pass into the stomach
• The lower esophageal sphincter closes to prevent reflux of gastric content into the esophagus
• Secondary esophageal peristalsis will initiate in the esophagus when remained food needs to be pushed into the stomach.

Dysphagia

• Difficulty in swallowing due to problems in the oropharynx or esophagus, possible coexistence with heartburn or vomiting

Types of Dysphagia

• Oropharyngeal dysphagia is a defect in initiation of swallowing at the pharynx and upper oesophageal sphincter
• Patient has difficulty initiating swallowing, and complains of choking and tracheal aspiration, nasal regurgitation
• Patients with Oesophageal dysphagia complain of food 'sticking' after swallowing, due to obstruction of the lumen or by defect in motility
• Swallowing of liquids is normal until strictures become extreme

Achalasia of the Oesophagus

• Absence of esophageal peristalsis and impaired relaxation of the lower esophageal sphincter (LES) in response to swallowing cause a functional obstruction at the gastroesophageal junction
• Causes: Damage in the neural network of the myenteric plexus in the lower 2/3 of the esophagus
• Suspected autoimmune disease

Clinical Features of Achalasia

• Regurgitation of food
• Difficulty for swallowing solids and eased by drinking liquids
• Absence of heartburn
• Episodes of chest pain due to oesophageal spasm

Gastroesophageal Reflux

• Stomach content backflow into the esophagus, and is a common condition

Anatomic Factors Which Prevent Reflux

• Oblique angle of entry of esophagus into the stomach
• Right crus of the diaphragm
• Mucosal folds of the esophagus
• Mucosal flap in the cardiac region of the stomach
• Low intra-abdominal pressure

Investigations for Gastroesophageal Reflux

• Barium swallow
• Esophageal manometry
• Prolonged esophageal pH monitoring
• Esophagogastroduodenoscopy to rule out cancer of the GEJ or fundus
• Concomitant endoscopic ultrasonography if a tumor is suspected

Complications of Gastroesophageal Reflux

• Oesophagitis
• Barrett's esophagus
• Benign esophageal stricture