Dysphagia can result from abnormalities in any of the complex steps necessary for swallowing. The process of swallowing has three stages.The first stage of swallowing begins in the mouth, where the tongue helps move the food around inside the mouth so that it can be chewed and softened with saliva. The tongue also is necessary for propelling the food to the back of the mouth and upper throat (pharynx) initiating the second stage.The second stage of swallowing is an automatic reflex that causes the muscles of the throat to propel the food through the throat (pharynx) and into the esophagus or swallowing tube. A muscular valve that lies between the lower throat and the top of the esophagus opens, allowing the food to enter the esophagus, while other muscles close the opening to the trachea to prevent food from entering the trachea and the lungs.The third stage of swallowing begins when food or liquid enters the esophagus. The esophagus is a muscular tube that connects the throat to the stomach and uses coordinated contractions of its muscles to push the food down its length and into the stomach. A second muscular valve opens at the junction of the lower esophagus with the stomach once a swallow has begun to allow the swallowed food to enter the stomach. After the food passes the valve closes again, preventing the food from regurgitating back up into the esophagus from the stomach.Dysphagia has many causes. First, there may be physical (anatomical) obstruction to the passage of food. Second, there may be abnormalities in the function (functional abnormalities) of the nerves of the brain, throat, and esophagus whose normal function is necessary to coordinate swallowing. Finally, there also may be abnormalities of the muscles of the throat and esophagus themselves.Diseases of the brain can affect the neurological control of the nerves and reflexes involved in swallowing. Some diseases of the brain that can cause dysphagia include:stroke,amyotropic lateral sclerosis,Parkinson's disease,multiple sclerosis,head injury, andcerebral palsy.Likewise, diseases and conditions that affect muscle function or connective tissue throughout the body can cause dysphagia. Examples include:muscular dystrophy,dermatomyositis,myasthenia gravis,scleroderma (systemic sclerosis), andSjogren's syndrome.Diseases specific to the esophagus also can cause difficulty swallowing. Some esophageal diseases include:achalasia, an uncommon inability of the lower esophageal sphincter (the valve at the lower end of the esophagus) to open and let food pass into the stomach and disappearance of the contractions of the esophagus that propel food;eosinophilic esophagitis, an inflammatory condition of the esophagus in which the esophageal wall is filled with a type of white blood cell called eosinophils; andother functional abnormalities of the muscle of the esophageal muscle including spasm and ineffective contractions.Obstructions of the upper digestive tract and esophagus, due to anatomical abnormalities, tumors, or scar tissue also cause dysphagia. Examples include:esophageal cancer;esophagitis (inflammation of the esophagus) though the symptom of esophagitis is more commonly odynophagia;certain head and neck cancers;esophageal strictures (narrowings of the esophagus) that result from inflammation and scarring most commonly from chronic acid exposure due to gastroesophageal reflux disease (GERD), but they also may arise due to radiation, medications, or chemical toxins;Schatzki rings (smooth, benign, circumferential, and narrow rings of tissue in the lower end of the esophagus that are located just above the junction of the esophagus with the stomach);compression of the esophagus from structures outside of the digestive tract, such as tumors of the chest, thoracic aortic aneurysms, enlarged lymph nodes, etc.; andcongenital anatomical abnormalities (birth defects).