PHARYNX

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THE PHARYNX (THROAT)
Is the part of the digestive system posterior to the nasal and oral cavities, extending inferiorly past the larynx. Is a muscular organ and contains a tube (a passage way) that is about 13cm long. It extends from the base of the skull to the inferior border of the cricoids cartilage anteriorly and the inferior border of C6 vertebra posteriorly. It has both digestive and respiratory functions and is divided into the nasopharynx, oropharynx and laryngopharynx. 

The nasopharynx is the nasal part of the pharynx; it lies superior to the soft palate and is the posterior extension of the nasal cavities. It is important in respiration.
The oropharynx is the oral part of the pharynx, and is bounded superiorly by the soft palate and inferiorly by the base of the tongue, laterally by the palatoglossal and palatopharyngeal arches. It extends from the inferior level of nasopharynx above to the superior border of the epiglottis. 

Laryngopharynx extends from the superior border of the epiglottis to the inferior border of the cricoids cartilage, where it narrows and becomes continous with the esophagus.

The pharyngeal mucosa is lined by stratified squamous epithelium. 
Pharyngeal Muscles:- the wall of the pharynx are composed of an external circular and internal longitudinal layer of muscles, but elsewhere in the alimentary canal the arrangement is opposite. The external circular layer of pharyngeal muscles consists of 3constrictors (the superior, middle and inferior constrictors). They constrict wall of the pharynx during swallowing.

The internal longitudinal layer of muscles consists of the palatopharnygeus, stylopharyngeus, and salpingopharyngeus. These muscles elevate the larynx and shorten the pharynx during swallowing and speaking.  

Blood supply
1. Ascending pharyngeal artery, a branch of the external carotid artery.
2. Branches of the inferior thyroid arteries
Venous return is via the internal jugular veins.

Nerve supply
Nerve supply is from the pharyngeal plexus which consist of sympathetic and parasympathetic nerve. The sympathetic nerve are from the cervical ganglia while the parasympathetic supply is chiefly from the glossopharyngeal and vagus nerves.

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