Pharynx and Pharygeal Structures
The pharynx is a tube made of fibers and muscle enclosing a musculomembranous lined passage continuous with the nasal cavity (nasal pharynx), oral cavity (oral pharynx), and the larynx (laryngeal pharynx). Accordingly, The pharynx is multi-functional. As a component of the digestive system, it aids food in beginning its passage to the stomach. It also helps route air to the larynx, trachea, and the lungs. Finally, the pharynx acts as a resonating chamber for the sounds produced in the larynx.
The outer walls of the pharynx are made of three circularly arranged muscles, which are called constrictors. The superior pharyngeal constrictor overlaps with the middle pharyngeal constrictor, which itself overlaps with the inferior pharyngeal constrictor. The arrangement has been described as three rings stacked one inside the other.
The inner walls of the pharynx are made of three muscles that are oriented in an up and down direction. These muscles are the stylopharyngeus, palatopharyngeus, and salptngopharyngeus. The first of this trio of muscles arises from a region outside the pharynx called the styloid process. It passes through the superior and middle constrictors into the pharynx. The second muscle originates in the soft region underneath the mouth and from the base of the tongue, and runs down the length of the pharynx. The last muscle originates at cartilage locate at the opening of the vocal tube.
The muscles of the pharynx function in eating. Successive contraction of the constrictors forces the ball of food down into the esophagus. The contraction of the longitudinal muscles causes the pharynx to rise. This acts to raise the pharynx up and around the chewed bolus (ball) of food. Between swallows the inferior constrictor may close to guard the entry to the esophagus and prevent unwanted entry of air. This muscle likely functions in a similar manner as the sphincter of the intestinal tract.
The pharynx is well supplied with blood, via the ascending pharyngeal arteries and branches of the superior and inferior thyroid arteries. Also, the area is well infused with nerves. This is to be expected, as the operation of the pharynx must be highly coordinated with eating, swallowing, and breathing.
The pharynx also contains specialized lymphatic tissue that acts as a barrier to microbial pathogens (disease-causing organisms). There are three types of this tissue. The nasopharyngeal tonsils, also known as the adenoids, are located in nasal pharynx. The palatine tonsils, which are familiar to many people simply as tonsils, are located in the oral pharynx. Finally, the lingual tonsils are located on the underside of the tongue.
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