The esophagus is a muscular tube connecting the throat (pharynx) with The upper esophageal sphincter (UES) is a bundle of muscles at the. Abstract. Deglutition or a swallow begins as a voluntary act in the oral cavity but proceeds autonomously in the pharynx and esophagus. Bilateral sequenced. Cover of Motor Function of the Pharynx, Esophagus, and its Sphincters in close anatomical relationship with the aorta, trachea, heart, and vertebral column.
Beneath its mucous membrane covering, each half of the tongue is composed of the same number and type of intrinsic and extrinsic skeletal muscles. The intrinsic muscles those within the tongue are the longitudinalis inferior, longitudinalis superior, transversus linguae, and verticalis linguae muscles. These allow you to change the size and shape of your tongue, as well as to stick it out, if you wish.
Having such a flexible tongue facilitates both swallowing and speech. As you learned in your study of the muscular system, the extrinsic muscles of the tongue are the mylohyoid, hyoglossus, styloglossus, and genioglossus muscles. These muscles originate outside the tongue and insert into connective tissues within the tongue. The mylohyoid is responsible for raising the tongue, the hyoglossus pulls it down and back, the styloglossus pulls it up and back, and the genioglossus pulls it forward.
Working in concert, these muscles perform three important digestive functions in the mouth: The top and sides of the tongue are studded with papillae, extensions of lamina propria of the mucosa, which are covered in stratified squamous epithelium Figure 2. Fungiform papillae, which are mushroom shaped, cover a large area of the tongue; they tend to be larger toward the rear of the tongue and smaller on the tip and sides.
Circumvallate papillae are much fewer in number, only 8 to 12, and lie in a row along the posterior portion of the tongue anterior to the lingual tonsil. In contrast, filiform papillae are long and thin. Fungiform and circumvallate papillae contain taste buds, and filiform papillae have touch receptors that help the tongue move food around in the mouth. Lingual glands in the lamina propria of the tongue secrete mucus and a watery serous fluid that contains the enzyme lingual lipase, which plays a minor role in breaking down triglycerides but does not begin working until it is activated in the stomach.
A fold of mucous membrane on the underside of the tongue, the lingual frenulum, tethers the tongue to the floor of the mouth. Severe ankyloglossia can impair speech and must be corrected with surgery. This superior view of the tongue shows the locations and types of lingual papillae.
The Salivary Glands Many small salivary glands are housed within the mucous membranes of the mouth and tongue. These minor exocrine glands are constantly secreting saliva, either directly into the oral cavity or indirectly through ducts, even while you sleep. In fact, an average of 1 to 1. Usually just enough saliva is present to moisten the mouth and teeth. Secretion increases when you eat, because saliva is essential to moisten food and initiate the chemical breakdown of carbohydrates.
Small amounts of saliva are also secreted by the labial glands in the lips. In addition, the buccal glands in the cheeks, palatal glands in the palate, and lingual glands in the tongue help ensure that all areas of the mouth are supplied with adequate saliva.
The Major Salivary Glands Outside the oral mucosa are three pairs of major salivary glands, which secrete the majority of saliva into ducts that open into the mouth: The submandibular glands, which are in the floor of the mouth, secrete saliva into the mouth through the submandibular ducts. The sublingual glands, which lie below the tongue, use the lesser sublingual ducts to secrete saliva into the oral cavity.
The parotid glands lie between the skin and the masseter muscle, near the ears.
Esophagus - Wikipedia
They secrete saliva into the mouth through the parotid duct, which is located near the second upper molar tooth Figure 3. Saliva Saliva is essentially Perhaps the most important ingredient in salvia from the perspective of digestion is the enzyme salivary amylase, which initiates the breakdown of carbohydrates. Food does not spend enough time in the mouth to allow all the carbohydrates to break down, but salivary amylase continues acting until it is inactivated by stomach acids.
Bicarbonate and phosphate ions function as chemical buffers, maintaining saliva at a pH between 6. Salivary mucus helps lubricate food, facilitating movement in the mouth, bolus formation, and swallowing.
Saliva contains immunoglobulin A, which prevents microbes from penetrating the epithelium, and lysozyme, which makes saliva antimicrobial.
For example, the parotid glands secrete a watery solution that contains salivary amylase.
The submandibular glands have cells similar to those of the parotid glands, as well as mucus-secreting cells. Therefore, saliva secreted by the submandibular glands also contains amylase but in a liquid thickened with mucus.
The sublingual glands contain mostly mucous cells, and they secrete the thickest saliva with the least amount of salivary amylase. The major salivary glands are located outside the oral mucosa and deliver saliva into the mouth through ducts. Mumps Infections of the nasal passages and pharynx can attack any salivary gland. The parotid glands are the usual site of infection with the virus that causes mumps paramyxovirus. Mumps manifests by enlargement and inflammation of the parotid glands, causing a characteristic swelling between the ears and the jaw.
The human esophagus has a mucous membrane consisting of a tough stratified squamous epithelium without keratina smooth lamina propriaand a muscularis mucosae.
In many animals the epithelium contains a layer of keratin, representing a coarser diet. The upper third of the esophagus contains striated musclethe lower third contains smooth muscleand the middle third contains a mixture of both. These are separated by the myenteric plexusa tangled network of nerve fibers involved in the secretion of mucus and in peristalsis of the smooth muscle of the esophagus.
The outermost layer of the esophagus is the adventitia in most of its length, with the abdominal part being covered in serosa. This makes it distinct from many other structures in the gastrointestinal tract that only have a serosa.
The ventral part of the embryo abuts the yolk sac. During the second week of embryological development, as the embryo grows, it begins to surround parts of the sac. The enveloped portions form the basis for the adult gastrointestinal tract. Over time, these arteries consolidate into the three main arteries that supply the developing gastrointestinal tract: The areas supplied by these arteries are used to define the midguthindgut and foregut.
Sections of this gut begin to differentiate into the organs of the gastrointestinal tract, such as the esophagus, stomachand intestines. The esophagus is thus one of the first components of the digestive system and the gastrointestinal tract. After food passes through the esophagus, it enters the stomach. At the same time, the upper esophageal sphincter relaxes, allowing a bolus of food to enter.
Peristaltic contractions of the esophageal muscle push the food down the esophagus. These rhythmic contractions occur both as a reflex response to food that is in the mouth, and also as a response to the sensation of food within the esophagus itself.
Along with peristalsis, the lower esophageal sphincter relaxes. Constriction of the upper and lower esophageal sphincters help to prevent reflux backflow of gastric contents and acid into the esophagus, protecting the esophageal mucosa. In addition, the acute angle of His and the lower crura of the diaphragm helps this sphincteric action.
Many genes with elevated expression are also shared with skin and other organs that are composed of squamous epithelia. For a more complete list, see esophageal disease.
Motor Function of the Pharynx, Esophagus, and its Sphincters - NCBI Bookshelf
Esophagitis Inflammation of the esophagus is known as esophagitis. Reflux of gastric acids from the stomach, infection, substances ingested for example, corrosivessome medications such as bisphosphonatesand food allergies can all lead to esophagitis. Esophageal candidiasis is an infection of the yeast Candida albicans that may occur when a person is immunocompromised.
As of [update] the cause of some forms of esophagitis, such as eosinophilic esophagitisis not known. Esophagitis can cause painful swallowing and is usually treated by managing the cause of the esophagitis - such as managing reflux or treating infection. Barrett's esophagus Prolonged esophagitis, particularly from gastric reflux, is one factor thought to play a role in the development of Barrett's esophagus.
In this condition, there is metaplasia of the lining of the lower esophagus, which changes from stratified squamous epithelia to simple columnar epithelia. Barrett's esophagus is thought to be one of the main contributors to the development of esophageal cancer.
Esophageal cancer There are two main types of cancer of the esophagus. Squamous cell carcinoma is a carcinoma that can occur in the squamous cells lining the esophagus. This type is much more common in China and Iran. The other main type is an adenocarcinoma that occurs in the glands or columnar tissue of the esophagus.
This is most common in developed countries in those with Barrett's esophagus, and occurs in the cuboidal cells. Inter-muscular septum that contains myenteric plexus resides in between the two muscle layers.
Esophagus is unique, unlike any other organ in the body, it is made up of partly skeletal and partly smooth muscles. Upper part is entirely skeletal 2—4 cmthe middle, a mixture of skeletal and smooth muscle Figure 9and the lower part, 11 cm or so in length is entirely smooth.
Upper esophageal sphincter is composed of all skeletal muscles and lower esophageal sphincter of all smooth muscles.
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Based on the studies in mice embryo, esophagus is comprised of entirely smooth muscles at the beginning that slowly transdifferentiate into the skeletal muscles during later embryological age until few days after birth [ 54 ]. However, this issue has been debated by other investigators [ 55 ]. Transdifferentiation of fully differentiated phenotype cells is not commonly seen in the other body tissue types and has been of significant interest to the developmental biologists.