Chapter 038. Dysphagia (Part 1) ppsx

Physiology of Swallowing The process of swallowing begins with a voluntary oral phase that includes a preparatory phase during which a food bolus suitable for swallowing is prepared and

Chapter 038 Dysphagia

(Part 1)

Harrison's Internal Medicine > Chapter 38 Dysphagia

Dysphagia: Introduction

Dysphagia is defined as a sensation of "sticking" or obstruction of the

passage of food through the mouth, pharynx, or esophagus However, it is often used as an umbrella term to include other symptoms related to swallowing

difficulty Aphagia signifies complete esophageal obstruction, which is usually due to bolus impaction and represents a medical emergency Difficulty in initiating

a swallow occurs in disorders of the voluntary phase of swallowing However,

once initiated, swallowing is completed normally Odynophagia means painful swallowing Frequently, odynophagia and dysphagia occur together Globus

pharyngeus is the sensation of a lump lodged in the throat However, no difficulty

is encountered when swallowing is performed Misdirection of food, resulting in

nasal regurgitation and laryngeal and pulmonary aspiration during swallowing, is

characteristic of oropharyngeal dysphagia Phagophobia, meaning fear of swallowing, and refusal to swallow may occur in hysteria, rabies, tetanus, and

pharyngeal paralysis due to fear of aspiration Painful inflammatory lesions that cause odynophagia may also cause refusal to swallow Some patients may feel the food as it goes down the esophagus This esophageal sensitivity is not associated with either food sticking or obstruction

Physiology of Swallowing

The process of swallowing begins with a voluntary (oral) phase that includes a preparatory phase during which a food bolus suitable for swallowing is prepared and a transfer phase during which the bolus is pushed into the pharynx

by contraction of the tongue The bolus then activates oropharyngeal sensory receptors that initiate the deglutition reflex The deglutition reflex is centrally mediated and involves a complex series of events It serves both to propel food through the pharynx and the esophagus and to prevent its entry into the airway When the bolus is propelled backward by the tongue, the larynx moves forward and the upper esophageal sphincter (UES) opens As the bolus moves into the pharynx, contraction of the superior pharyngeal constrictor against the contracted soft palate initiates a peristaltic contraction that proceeds rapidly downward to move the bolus through the pharynx and the esophagus The lower esophageal sphincter (LES) opens as the food enters the esophagus and remains open until the

peristaltic contraction has swept the bolus into the stomach Peristaltic contraction

in response to a swallow is called primary peristalsis It involves inhibition

followed by sequential contraction of muscles along the entire swallowing passage The inhibition that precedes the peristaltic contraction is called

deglutitive inhibition Local distention of the esophagus from residual food

activates secondary peristalsis

Muscles of the oral cavity, pharynx, UES, and cervical esophagus are striated and are directly innervated by the lower motor neurons carried in the cranial nerves Oral cavity muscles are innervated by the Vth and the VIIth cranial nerves and the tongue muscles by the XIIth cranial nerve Pharyngeal muscles are innervated by the IXth and the Xth cranial nerves

The UES consists of constrictor and dilator muscles The constrictor muscles include the cricopharyngeus and inferior pharyngeal constrictor muscles The dilator muscles include a number of suprahyoid muscles including the geniohyoid muscle The constrictor muscles are innervated by the Xth cranial nerves and the dilator muscles are innervated by the XIIth and also the Vth and the VIIth cranial nerves The UES remains closed owing to the elastic properties of its wall and to neurogenic tonic contraction of the cricopharyngeus muscle Inhibition

of the vagal excitatory activity in the central nervous system relaxes the cricopharyngeus, and contraction of the dilator muscles opens the UES by causing upward and forward displacement of the larynx

The neuromuscular apparatus for peristalsis is different in cervical and thoracic parts of the esophagus The cervical esophagus, like the pharyngeal muscles, is composed of striated muscles and is innervated by lower motor neurons in the vagus (Xth cranial) nerve Peristalsis in the cervical esophagus is due to sequential activation of the vagal motor neurons in the nucleus ambiguus

In contrast, the thoracic esophagus and LES are composed of smooth-muscle fibers and are innervated by excitatory and inhibitory neurons within the esophageal myenteric plexus Neurotransmitters of the excitatory nerves are acetylcholine and substance P, and of the inhibitory nerves are vasoactive intestinal peptide (VIP) and nitric oxide Separate groups of parasympathetic preganglionic nerve fibers in the Xth cranial nerve arising from its dorsal motor nucleus project onto the inhibitory and excitatory postganglionic myenteric neurons Patterned activation of inhibitory followed by excitatory vagal pathways

is responsible for peristalsis, which consists of a sequence of inhibition (deglutitive inhibition) followed by contraction The LES relaxes, with deglutitive inhibition, at the onset of esophageal peristalsis

The LES is closed at rest because of its intrinsic myogenic tone, influenced

by excitatory and inhibitory nerves The function of the LES is supplemented by the striated muscle of the diaphragmatic crura, which surrounds the LES and acts

as an external LES