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Pharynx and Esophagus

Pharynx

  •  The pharynx is a cone-shaped passageway that leads from the oral and nasal cavity to the esophagus and larynx. The three parts of the pharynx are the nasopharynx, oropharynx, and the laryngopharynx. The nasopharynx is the most anterior portion and located in the back of the nasal cavity. The nasopharynx connects to the oropharynx, by means of passage called an isthmus. The oropharynx begins in the back of the oral cavity and continues down the throat to the epiglottis. The third region is the laryngopharynx, which begins at the epiglottis and extends all the way to the esophagus. Its function is to regulate the passage of air to the lungs and food to the esophagus. 
  • Tissue: The nasopharynx is lined with psuedostratified columnar epithelium while the oropharynx and laryngopharynx are both lined with stratified squamous epithelium.
  • Digestion:  Within the pharynx, nothing is digested or absorbed, as it acts as a passage way from the oral cavity to the esophagus to make its way down to the stomach. 
  • Nasopharynx: This is the upper portion of the pharynx, which extends from the base of the skull to the upper surface of the soft palate. In between the internal nares and the soft palate is the oral cavity. The adenoids, which are lymphoid tissue structures, are loacated in the posterior wall of the nasopharynx. Polyps or mucus can obstruct the nasopharynx, as can congestion due to an upper respiratory infection. 
  • Oropharynx: The oropharynx lies behind the oral cavity, extending from the uvula to the level of the hyoid bone. It opens anteriorly, through the isthmus faucium, into the mouth, while in its lateral wall, between the palatoglossal arch and the palatopharyngeal arch, is the palatine tonsil. The anterior wall is composes of the base of the tongue and the epiglottic vallecula. The lateral wall consists of the tonsil, tonsillar pillars, and the superior wall is made up of the inferior surface of the soft palate and the uvula. Because both food and air pass through the pharynx, a flap of connective tissue called the epiglottis closes over the glottis when food is swallowed to prevent aspiration. 
  • Laryngopharynx: This is the part of the throat that connects to the esophagus. It lies inferior to the epiglottis and extends to the location where this common pathway diverges into the respiratory and digestive pathways. The laryngopharynx is continuous with the esophagus posteriorly.  There are three major sites within the laryngopharynx: the pyriform sinus, postcricoid area, and the posterior pharyngeal wall. 
 Rat Shark Human
 Located in the back of the mouth, functions with both eating and breathingAssists in swallowing and allows for incoming water to pass onto the gills. Allows for food and water to begin its digestive tract by permitting it into the esophagus while also helping with repsiration to deliver air to the trachea
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Esophagus

  • Tissue: The inner wall of the esophagus is lined with stratified squamous epithelium tissue. External to the epithelial layer is loose connective tissue. 
  • Enzymes: There are no enzymes released by the esophagus because it is a path to the abdomen. The esophagus is a tube that passed food from the pharynx to the stomach. 
  • Digestion: After being swallowed, the chewed food is pushed down the esophagus to the stomach through contraction of the muscles. It only takes about 7 seconds for the food to pass through the esophagus. Food is not digested in this area, as it acts as a pathway to the stomach.
  • The esophagus is a muscular tube that connects the pharynx to the stomach. This tube is usually 8 inches long and is lined with moist pink tissue called mucosa. The esophagus is posterior to the throat and heart, and anterior to the spine. Right before the stomach, the esophagus passes through the diaphragm. The upper esophageal sphincter dilates to permit the swallowed substances to enter the esophagus. From then on, there are waves of muscle contractions called peristalsis that allow the food to move toward the stomach. A final function of the esophagus is its participation in the vomiting reflex to void the contents of the stomach. 

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  Diagram of the Esophagus
Rat Shark Human
 Passes food from pharynx to stomach Passes food from pharynx to stomach Passes food from pharynx to stomach
Cannot vomit because rats have a powerful barrier between the stomach and the esophagus and the esophageal muscles are not strong enough to break the barrier. Also, vomiting requires the two muscles of the diaphragm to contract but it does not seem like the rat is capable of doing this. Sharks are capable of vomiting,but they only vomit undigested foods, such as large bones or perhaps rubbish that they swallow. Humans are able to vomit.

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