Esophagus

Esophagus

Overview
The esophagus is an organ
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...

 in vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s which consists of a muscular
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

 tube through which food passes from the pharynx
Human pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...

 to the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...

. During swallowing
Swallowing
Swallowing, known scientifically as deglutition, is the process in the human or animal body that makes something pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. If this fails and the object goes through the trachea, then choking or pulmonary aspiration...

, food passes from the mouth through the pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...

 into the esophagus and travels via peristalsis
Peristalsis
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...

 to the stomach. The word esophagus is derived from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 œsophagus, which derives from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 word oisophagos , lit. "entrance for eating." In humans the esophagus is continuous with the laryngeal
Larynx
The larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...

 part of the pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...

 at the level of the C6 vertebra.
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Encyclopedia
The esophagus is an organ
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...

 in vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s which consists of a muscular
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

 tube through which food passes from the pharynx
Human pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...

 to the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...

. During swallowing
Swallowing
Swallowing, known scientifically as deglutition, is the process in the human or animal body that makes something pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. If this fails and the object goes through the trachea, then choking or pulmonary aspiration...

, food passes from the mouth through the pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...

 into the esophagus and travels via peristalsis
Peristalsis
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...

 to the stomach. The word esophagus is derived from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 œsophagus, which derives from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 word oisophagos , lit. "entrance for eating." In humans the esophagus is continuous with the laryngeal
Larynx
The larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...

 part of the pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...

 at the level of the C6 vertebra. The esophagus passes through posterior mediastinum in thorax and enters abdomen through a hole in the diaphragm at the level of the tenth thoracic vertebrae (T10). It is usually about 25–30 cm long depending on individual height. It is divided into cervical, thoracic and abdominal parts. Due to the inferior pharyngeal constrictor muscle
Inferior pharyngeal constrictor muscle
The Inferior pharyngeal constrictor, the thickest of the three constrictors, arises from the sides of the cricoid and thyroid cartilage. Similarly to the superior and middle pharyngeal constrictor muscles, it is innervated by the vagus nerve , specifically, by branches from the pharyngeal plexus...

, the entry to the esophagus opens only when swallowing or vomiting.

Histology



The layers of the esophagus are as follows:
  • mucosa
    • nonkeratinized stratified squamous epithelium
      Stratified squamous epithelium
      A stratified squamous epithelium consists of squamous epithelial cells arranged in layers upon a basement membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural integrity...

      : is rapidly turned over, and serves a protective effect due to the high volume transit of food, saliva
      Saliva
      Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...

       and mucus
      Mucus
      In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...

      .
    • lamina propria
      Lamina propria
      The lamina propria is a constituent of the moist linings known as mucous membranes or mucosa, which line various tubes in the body ....

      : sparse.
    • muscularis mucosae
      Muscularis mucosae
      The lamina muscularis mucosae is the thin layer of smooth muscle found in most parts of the gastrointestinal tract, located outside the lamina propria mucosae and separating it from the submucosa....

      : smooth muscle
      Smooth muscle
      Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...

  • submucosa
    Submucosa
    In the gastrointestinal tract, the submucosa is the layer of dense irregular connective tissue or loose connective tissue that supports the mucosa, as well as joins the mucosa to the bulk of underlying smooth muscle .-Contents:Blood vessels, lymphatic vessels, and nerves will run through...

    : Contains the mucous secreting glands (esophageal glands
    Esophageal glands
    The esophageal glands are small compound racemose exocrine glands of the mucous type.They are lodged in the submucous tissue, and each opens upon the surface by a long excretory duct....

    ), and connective structures termed papillae.
  • muscularis externa
    Muscularis externa
    The muscular coat is a region of muscle in many organs in the vertebrate body, adjacent to the submucosa membrane...

    (or "muscularis propria"): composition varies in different parts of the esophagus, to correspond with the conscious control over swallowing
    Swallowing
    Swallowing, known scientifically as deglutition, is the process in the human or animal body that makes something pass from the mouth, to the pharynx, and into the esophagus, while shutting the epiglottis. If this fails and the object goes through the trachea, then choking or pulmonary aspiration...

     in the upper portions and the autonomic control in the lower portions:
    • upper third, or superior part: striated muscle
      Striated muscle
      Striated muscle tissue is a form of fibers that are combined into parallel fibers. More specifically, it can refer to:* Cardiac muscle .* Skeletal muscle* Branchiomeric muscles...

    • middle third, smooth muscle
      Smooth muscle
      Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...

       and striated muscle
      Striated muscle
      Striated muscle tissue is a form of fibers that are combined into parallel fibers. More specifically, it can refer to:* Cardiac muscle .* Skeletal muscle* Branchiomeric muscles...

    • inferior third: predominantly smooth muscle
  • adventitia
    Adventitia
    Adventitia is the outermost connective tissue covering of any organ, vessel, or other structure. It is also called the tunica adventitia or the tunica externa....


Esophageal constrictions


Normally, the esophagus has three anatomic constrictions at the following levels;
  • At the esophageal inlet, where the pharynx
    Pharynx
    The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...

     joins the esophagus, behind the cricoid cartilage (14-16 cm from the incisor teeth).
  • Where its anterior surface is crossed by the aortic arch
    Aortic arch
    The arch of the aorta or the transverse aortic arch is the part of the aorta that begins at the level of the upper border of the second sternocostal articulation of the right side, and runs at first upward, backward, and to the left in front of the trachea; it is then directed backward on the left...

     and the left bronchus
    Bronchus
    A bronchus is a passage of airway in the respiratory tract that conducts air into the lungs. The bronchus branches into smaller tubes, which in turn become bronchioles....

      (25-27 cm from the incisor teeth).
  • Where it pierces the diaphragm
    Diaphragm
    -Optics and photography:* Diaphragm , a stop in the light path of a lens, having an aperture that regulates the amount of light that passes* Diaphragm shutter, a type of leaf shutter consisting of a number of thin blades in a camera-Acoustics:...

      (36-38 cm from the incisor teeth).


The distances from the incisor teeth are important as is useful for diagnostic endoscopic
Endoscopy
Endoscopy means looking inside and typically refers to looking inside the body for medical reasons using an endoscope , an instrument used to examine the interior of a hollow organ or cavity of the body. Unlike most other medical imaging devices, endoscopes are inserted directly into the organ...

 procedures.

Gastroesophageal junction


The junction between the oesophagus and the stomach (the gastroesophageal junction or GE junction) is not actually considered a valve, although it is sometimes called the cardiac sphincter, cardia
Cardia
The cardia is the anatomical term for the part of the stomach attached to the esophagus. The cardia begins immediately distal to the z-line of the gastroesophageal junction, where the squamous epithelium of the esophagus gives way to the columnar epithelium of the gastrointestinal tract.Just...

 or cardias, it actually better resembles a structure.

In much of the gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....

, smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...

s contract in sequence to produce a peristaltic wave which forces a ball of food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...

 (called a bolus
Bolus (digestion)
In digestion, a bolus is a mass of food that has been chewed at the point of swallowing. Once a bolus reaches the stomach, digestion begins....

) while in the esophagus. In humans, peristalsis
Peristalsis
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...

 is found in the contraction of smooth muscles to propel contents through the digestive tract.

In other animals


In most fish, the oesophagus is extremely short, primarily due to the length of the pharynx (which is associated with the gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s). However, some fish, including lamprey
Lamprey
Lampreys are a family of jawless fish, whose adults are characterized by a toothed, funnel-like sucking mouth. Translated from an admixture of Latin and Greek, lamprey means stone lickers...

s, chimaera
Chimaera
Chimaeras are cartilaginous fish in the order Chimaeriformes, known informally as ghost sharks, ratfish , spookfish , or rabbitfishes...

s, and lungfish
Lungfish
Lungfish are freshwater fish belonging to the Subclass Dipnoi. Lungfish are best known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive within Sarcopterygii, including the presence of lobed fins with a well-developed...

, have no true stomach, so that the esophagus effectively runs from the pharynx directly to the intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...

, and is therefore somewhat longer.

In tetrapod
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...

s, the pharynx is much shorter, and the esophagus correspondingly longer, than in fish. In amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...

s, shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

s and rays, the esophageal epithelium is ciliated, helping to wash food along, in addition to the action of muscular peristalsis. In the majority of vertebrates, the esophagus is simply a connecting tube, but in bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s, it is extended towards the lower end to form a crop
Crop (anatomy)
A crop is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion that is found in many animals, including gastropods, earthworms, leeches, insects, birds, and even some dinosaurs.- Bees :Cropping is used by bees to temporarily store nectar of flowers...

 for storing food before it enters the true stomach.

A structure with the same name is often found in invertebrates, including molluscs and arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...

s, connecting the oral cavity with the stomach.

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