The initiation of the swallowing reflex involves various movements in the pharyngeal phase that occur within a second. These movements include the upward pull of the soft palate and inward movement of the palatopharyngeal folds. Additionally, the tongue thrusts up and back, the nasopharynx closes, the larynx elevates, and the airway closes. Simultaneously, the pharynx contracts, and the bolus moves through the pharynx and upper esophageal sphincter (UES) before entering the esophagus.

Xerostomia, or dry mouth, can result from impaired salivary secretion, which may be congenital or caused by an autoimmune process. Decreased secretion leads to a lower pH in the oral cavity, contributing to tooth decay and esophageal erosions. It also causes difficulties in swallowing.

The measurement and monitoring of various molecular components in saliva can aid in the diagnosis and monitoring of overall health. Saliva collection is noninvasive and easily accessible. Saliva can help identify biomarkers indicating the presence of diseases and track the progress of individuals undergoing treatment. For example, levels of steroids such as cortisol, estradiol, progesterone, and testosterone can be measured in their free form in saliva. Saliva can also be used to detect viral infections like HIV, herpes, hepatitis C, and Epstein-Barr virus through polymerase chain reaction (PCR) techniques. Similarly, bacterial infections like Helicobacter pylori can be detected in saliva, and saliva can be used to monitor drug levels.

To ensure food does not enter the nasopharynx and allow passage into the pharynx, the vocal cords are pulled together and the larynx is moved forward and upward against the epiglottis. These actions also aid in opening the upper esophageal sphincter (UES). Subsequently, the UES relaxes to receive the food bolus. The superior constrictor muscles of the pharynx contract strongly, propelling the bolus deep into the pharynx. This initiates a peristaltic wave that moves towards the esophagus, pushing the bolus through the relaxed UES. During the pharyngeal stage of swallowing, respiration is reflexively inhibited, and the sphincter constricts after the bolus passes through the UES.

Gastroesophageal reflux disease (GERD), commonly known as heartburn or indigestion, occurs when the lower esophageal sphincter allows the acidic contents of the stomach to reflux into the distal part of the esophagus. Unlike the stomach, the esophagus lacks a robust system to protect its mucosal lining. Consequently, the acid activates pain fibers, resulting in discomfort and pain. Although even healthy individuals may experience this occasionally, continuous reflux can lead to mucosal damage, classifying the condition as GERD. Treatment options for GERD include H2 receptor antagonists that reduce gastric acid secretion (e.g., ranitidine [Zantac]) and proton pump inhibitors (e.g., omeprazole [Prilosec]).

The esophagus, UES, and lower esophageal sphincter (LES) serve two primary functions.
that initiate the swallowing reflex. The pharyngeal phase of swallowing involves the following sequence of events, which occur in less than 1 second: 1. The soft palate is pulled upward and the palatopharyngeal folds move inward toward one another; these movements 0.2 0.4 0.6 0.8 1.0 1.2 Time (sec) Bolus in mouth Bolus moves through pharynx and UES Bolus enters esophagus Tongue thrust up and back Nasopharynx closed Larynx elevated Airway closed UES open Pharynx contracts • Fig. 28.5 Timing of motor events in the pharynx and UES during a swallow.
Xerostomia, or dry mouth, is caused by impaired salivary secretion. It can be congenital or develop as part of an autoimmune process. The decrease in secretion reduces the pH in the oral cavity, which causes tooth decay and is associated with esophageal erosions. Reduced secretion also causes difficulty swallowing.
The ability to measure and monitor a wide range of molecular components that are indicative of overall health is useful in diagnosis and monitoring. Saliva is easy to access, and collection of it is noninvasive. It is used to identify individuals with disease (presence of biomarkers) and to monitor the progress of affected individuals under treatment. In endocrinology, levels of steroids can be measured in the free form rather than as the free and bound form, as in plasma (e.g., the stress hormone cortisol and the sex hormones estradiol, progesterone, and testosterone). Viral infections such as human immunodeficiency virus (HIV), herpes, hepatitis C, and Epstein-Barr virus infection can be detected by polymerase chain reaction (PCR) techniques. Bacterial infections, such as Helicobacter pylori, can likewise be detected in saliva, and saliva is also used for monitoring drug levels.
prevent reflux of food into the nasopharynx and open a narrow passage through which food moves into the pharynx.
2. The vocal cords are pulled together and the larynx is moved forward and upward against the epiglottis; these actions prevent food from entering the trachea and help open the upper esophageal sphincter (UES).
3.
The UES relaxes to receive the bolus of food.
4.
The superior constrictor muscles of the pharynx then contract strongly to force the bolus deeply into the pharynx. A peristaltic wave is initiated with contraction of the pharyngeal superior constrictor muscles, and the wave moves toward the esophagus. This wave forces the bolus of food through the relaxed UES. During the pharyngeal stage of swallowing, respiration is also reflexively inhibited. After the bolus of food passes the UES, a reflex action causes the sphincter to constrict.
Gastroesophageal reflux disease (GERD) is commonly referred to as heartburn or indigestion. It occurs when the lower esophageal sphincter allows the acidic contents of the stomach to reflux back into the distal part of the esophagus. This region of the esophagus, unlike the stomach, does not have a robust system to protect the mucosal lining. Thus the acid will activate pain fibers and thereby result in discomfort and pain. This is not an uncommon phenomenon, even in healthy individuals. In the long term, continual reflux can result in damage to the esophageal mucosa. In this case, this condition is classed as GERD and can be treated by H2 receptor antagonists that reduce gastric acid secretion (e.g., ranitidine [Zantac]) or by proton pump inhibitors (e.g., omeprazole [Prilosec]).
The esophagus, the UES, and the lower esophageal sphincter (LES) serve two main functions (