What is the anatomy and clinical significance of the tongue?

Tongue Anatomy and Clinical Significance

Structural Overview

The tongue is a complex muscular organ composed of striated muscle that occupies the floor of the mouth, with its dorsal surface covered by stratified squamous epithelium containing numerous papillae and taste buds. 1 The tongue is attached to the floor of the mouth by a fold called the frenulum and typically features 8-12 circumvallate papillae arranged in an inverted V-shape toward the base. 1

• The tongue functions as a muscular hydrostat—a complex organ crucial for maintaining airway patency, preparing and safely transporting food/liquid, and rapidly changing position and shape for speech. 2
• The anterior two-thirds of the tongue is part of the oral cavity proper, with rich lymphatic drainage to nodal groups at levels I through III. 3
• The tongue base extends posteriorly and plays a critical role in pharyngeal phase swallowing mechanics. 3

Functional Roles in Swallowing

The tongue performs critical functions across all phases of swallowing, with dysfunction leading to significant morbidity including aspiration pneumonia, malnutrition, and mortality. 3

Oral Phase Functions

• During the oral preparatory phase, the tongue works with the lips and mandible to masticate food and mix it with saliva to form a cohesive bolus. 3
• In the oral propulsive phase, the muscular tongue contacts the hard palate to slide the bolus posteriorly under positive pressure toward the pharynx. 3
• The tongue is under voluntary skeletal muscle control during these phases, requiring an alert, participating patient. 3

Pharyngeal Phase Functions

• The tongue pushes backward and downward into the pharynx to provide positive pressure to propel the bolus, with the base of tongue retracting to the posterior pharyngeal wall. 3
• This tongue base retraction is a critical component of the pharyngeal swallow response that occurs within 1-2 seconds. 3
• Reduced tongue base retraction is a common impairment leading to vallecular residue and increased aspiration risk. 3

Developmental Considerations

For the first 3 months of life, the tongue acts as a piston within a cylinder to facilitate sucking on a nipple, with mature swallowing patterns not achieved until ages 5-8 years. 3

• Infants can breathe and swallow simultaneously due to the more superior location of the larynx and shorter pharyngeal length, an ability lost with maturity. 3
• The ability to form a solid food bolus develops as oral pharyngeal structures mature, with biting achieved at approximately 7 months and chewing at 10-12 months. 3
• Children achieve adult patterns of muscle activation during swallowing by electromyography at ages 5-8 years. 3

Clinical Significance in Dysphagia

Tongue dysfunction is a primary contributor to oral-pharyngeal dysphagia, which results in aspiration, pneumonia, malnutrition, dehydration, and reduced quality of life. 3

Key Tongue-Related Impairments

• Reduced tongue strength is identified as a risk factor for aspiration, with tongue strength declining in healthy aging. 3
• Decreased tongue base retraction leads to vallecular residue and inadequate bolus propulsion. 3
• Impaired tongue coordination affects bolus formation and control during the oral preparatory phase. 3

Therapeutic Interventions

• Tongue strength training has demonstrated improvements in swallowing variables including vallecular residues and swallowing safety in cohort studies. 3
• The effortful swallow technique increases tongue base retraction pressure, hyolaryngeal excursion, and lingual pressures in patients with residue. 3
• The chin-down posture approximates the tongue base toward the pharyngeal wall and reduces aspiration risk by approximately 50% in patients with aspiration. 3

Systemic and Disease Relationships

The tongue serves as both a motor and sensory organ with autocrine/paracrine mechanisms that interact with the whole body system, and may harbor signs of systemic disease. 4, 5

• The tongue and its taste apparatus form part of an innate immune surveillance system, with loss or alteration in taste perception serving as an early indication of infection (as evidenced during SARS-CoV-2 pandemic). 4
• The oral cavity and tongue are sites of neoplasms, reactive processes, and infections, and may be harbingers of systemic diseases including nutritional deficiencies and systemic amyloidosis. 6
• Tongue action affects lower limb muscle strength and posture, extending its influence beyond the oral cavity. 5

Clinical Pitfalls

• Silent aspiration (aspiration without cough response) is common in patients with impaired laryngeal sensation, making tongue dysfunction particularly dangerous. 3
• In neonates and infants, aspiration presents with subtle signs (apnea and increased swallowing frequency) rather than cough, contributing to significant mortality rates. 3
• Occult neck metastasis is common (50-60%) in patients with anterior tongue cancers due to rich lymphatic supply, necessitating careful evaluation. 3