**3. Anatomy and function of the esophagus**

The esophagus is a muscular tube that can be divided into three anatomic areas: The pars cervicalis, pars thoracica, and pars abdominalis. It has two layers of muscles - the inner circular and outer longitudinal. The proximal portion of the esophagus consists of striated muscle, distal smooth muscle, and a middle part consisting of smooth and striated muscles.

In terms of nerves, the esophagus is innervated from the plexus esophageus that consists of a large number of nerves of different diameters covering the area from the nn. vagi via nn. laryngei recurrentes. Branches provide connections with four or five cranial ganglia of the upper section of truncus sympathicus. These are autonomous fibers with a smaller component of sensory fibers. Plexus esophageus is located on the surface of the esophagus and continues caudally to truncus vagalis anterior and posterior. Both front and rear truncus vagalis contain left and right vagus nerve fibers.

Afferent signals apparent during the swallowing reflex are directed from sensitive fibers of the trigeminal nerve, n. glossopharyngeus and n. vagus. Efferent arm is successively comprised of the nerve hypoglossal motor fibers, n. trigeminus, n. facialis, n. glossopharyngeus and the n. vagus.

In terms of functions, the esophagus can be divided into the upper esophageal sphincter, the muscle's own tube (body), and the lower esophageal sphincter. All these parts play an important role with the following functions: Transport and swallowing, removal of gastric contents, and prevention of tracheobronchial aspiration.

Swallowing is divided into three phases:

*An oral phase*, which is a voluntary act that proceeds as the food or liquid is shifted towards the larynx.

*A pharyngeal phase* in which the muscles of the larynx and pharynx close all openings except the Killian sphincter where the food is passed.

*An esophageal phase.* Shortly after the contraction of the pharynx, the upper sphincter of the esophagus flags at about 0.5 seconds and at this time it creates a primary peristaltic wave. In about two seconds, the lower esophageal sphincter is extended and then relaxed for 5 to 10 seconds. Relaxation is terminated with a contraction lasting about a tenth of a second. In addition to the primary peristaltic wave, there is a secondary peristaltic contraction that forces regurgitated food or liquid. During swallowing, the upper sphincter closes periodically.

In the first phase of the voluntary swallowing act, food is transported from the mouth into the pharynx by the tongue's pressure against the palate with lips and teeth together. The tongue and soft palate shape the food during this process. Cranial hyoid bone muscles raise the hyoid bone with pharynx. The bite of food then inches behind the isthmus faucium and the second phase begins.

The second phase is involuntary reflex and begins as the soft palate makes contact with food or liquid. The soft palate rises and stretches along the upper pharyngeal constrictors closing the nasopharynx from the oral cavity. Mm. constrictores pharyngis (medius et inferior) shift the food, mm levatores rise up the pharynx with the larynx, the epiglottis is bending, and closes before the food passes the aditus laryngis.

The esophagus is a muscular tube that can be divided into three anatomic areas: The pars cervicalis, pars thoracica, and pars abdominalis. It has two layers of muscles - the inner circular and outer longitudinal. The proximal portion of the esophagus consists of striated muscle, distal smooth muscle, and a middle part consisting of smooth and striated muscles. In terms of nerves, the esophagus is innervated from the plexus esophageus that consists of a large number of nerves of different diameters covering the area from the nn. vagi via nn. laryngei recurrentes. Branches provide connections with four or five cranial ganglia of the upper section of truncus sympathicus. These are autonomous fibers with a smaller component of sensory fibers. Plexus esophageus is located on the surface of the esophagus and continues caudally to truncus vagalis anterior and posterior. Both front and rear truncus

Afferent signals apparent during the swallowing reflex are directed from sensitive fibers of the trigeminal nerve, n. glossopharyngeus and n. vagus. Efferent arm is successively comprised of the nerve hypoglossal motor fibers, n. trigeminus, n. facialis, n.

In terms of functions, the esophagus can be divided into the upper esophageal sphincter, the muscle's own tube (body), and the lower esophageal sphincter. All these parts play an important role with the following functions: Transport and swallowing, removal of gastric

*An oral phase*, which is a voluntary act that proceeds as the food or liquid is shifted towards

*A pharyngeal phase* in which the muscles of the larynx and pharynx close all openings except

*An esophageal phase.* Shortly after the contraction of the pharynx, the upper sphincter of the esophagus flags at about 0.5 seconds and at this time it creates a primary peristaltic wave. In about two seconds, the lower esophageal sphincter is extended and then relaxed for 5 to 10 seconds. Relaxation is terminated with a contraction lasting about a tenth of a second. In addition to the primary peristaltic wave, there is a secondary peristaltic contraction that forces regurgitated food or liquid. During swallowing, the upper sphincter closes periodically.

In the first phase of the voluntary swallowing act, food is transported from the mouth into the pharynx by the tongue's pressure against the palate with lips and teeth together. The tongue and soft palate shape the food during this process. Cranial hyoid bone muscles raise the hyoid bone with pharynx. The bite of food then inches behind the isthmus faucium and

The second phase is involuntary reflex and begins as the soft palate makes contact with food or liquid. The soft palate rises and stretches along the upper pharyngeal constrictors closing the nasopharynx from the oral cavity. Mm. constrictores pharyngis (medius et inferior) shift the food, mm levatores rise up the pharynx with the larynx, the epiglottis is bending, and

**3. Anatomy and function of the esophagus** 

vagalis contain left and right vagus nerve fibers.

contents, and prevention of tracheobronchial aspiration.

glossopharyngeus and the n. vagus.

Swallowing is divided into three phases:

the Killian sphincter where the food is passed.

closes before the food passes the aditus laryngis.

the larynx.

the second phase begins.

In the next phase, which is a continuation of the swallowing reflex and is not considered a separate phase, the lower pharyngeal sphincter activity shifts the bite to the beginning of the esophagus, followed by transport due to esophageal muscle activity. Elevated pharynx and larynx return caudally. At the same time, swallowing ventilates the middle-ear cavity. Transport of food from the mouth into the upper esophagus is related to the coordinated relaxation of the upper esophageal sphincter, which is a consequence of inhibitory signals from the masticatory center through n. vagus. Sphincter tone can be influenced by local factors such as pH in the esophagus.

In the third phase, food is propelled by the coordinated peristaltic wave of esophagus muscles that move aborally at the rate of 3 cm/s when the lower esophageal sphincter is relaxed. Peristaltic wave speed is affected by many factors, especially by the temperature and volume of the swallowed food. If the interval between swallowing two mouthfuls is less than 10 seconds, swallowing is often not followed by a peristaltic wave.

The lower esophageal sphincter is a smooth muscle area with a length of 3 cm that separates the esophagus from the stomach. It prevents reflux of gastric contents back into the esophagus during swallowing and performs coordinated relaxation allowing the passage of food from the esophagus to the stomach. Its activity can be influenced by myogenic, neural, and humoral factors. The pressure increase is caused by gastrin, motilin, prostaglandin, and histamine. By contrast, a reduction occurs under the influence of cholecystokinine, secretine, glucagone, progesterone, neurotensin. The physiological significance of some of these substances is questionable.

The function of the esophagus is affected by autonomic innervation activity. The enteric system is relatively independent and regulates many functions of the digestive tube. Enteric system (myenteric and submucous) is under the influence of signals from CNS and receptors in the tube wall (mechanoreceptors, chemoreceptors, and thermoreceptors) (Bharucha & Camilleri, 2003, Bielefeldt & Gebhart, 2004).

The autonomic nervous system does not work separately from cortical and subcortical structures. The peripheral autonomic nervous system function is subject - to a large extent to the regulations of the central nervous system (except the voluntary control), which provides a comprehensive and targeted response. Another function of the digestive tube modulation is the relationship between the enteric nervous system, central nervous system, and the immune system in the gastrointestinal tract. This can explain the influence of stress on the occurence or worsening of symptoms in the digestive tract.
