Pharynx - Anatomy & Physiology
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Introduction
The pharynx is part of both the respiratory and digestive system. Both systems have entrances to the pharynx but they are separated from each other by the soft palate. The section that is rostral to the sort palate is known as the nasopharynx.
During exercise or during respiratory distress, the mouth can be used as an additional opening of the respiratory system and then the oropharynx also becomes an air-way.
The pharynx can be split into different regions- the oropharynx, laryngeal pharynx (sometimes referred to as the oesophageal pharynx) and the nasopharynx
Structure and Function
- Opening of the larynx is on the floor of the pharynx
- Caudal and dorsal to the laryngeal opening is the opening into the oesophagus
- In the dorsal region of the nasopharynx there are paired openings into the Auditory (Eustacian) Tubes
- The lining of the middle ear cavity and auditory tube is continuous with that of the nasopharynx
- Located between the base of the skull and the first two cervical vertebrae dorsally
- larynx ventrally
- Mandible, pterygoid muscles and hyoid apparatus laterally
- Walls contain striated muscle
- During swallowing the soft palate is raised which divides the pharynx into dorsal and ventral sections
- Laterally, two pairs of palatopharyngeal arches are present from the soft palate to the oesophagus
- The dorsal compartment is the nasopharynx
- The rostral compartment is the oropharynx
- The laryngeal pharynx is separated from the oropharynx by the epiglottis
- Tonsils are present on the lateral walls of the oropharynx
- Covered by flaps of mucosa
- Partially visible in the open mouth
- The pharynx plays an important role in deglutition
Musculature
Muscles that constrict
- Run dorsally to roof of pharynx
- Rostral constrictor muscles are the hyopharyngeous, pterygopharyngeous and the palatopharyngeous muscles
- Originate from the pterygoid region of the skull and the aponeurosis of the soft palate
- Shorten the pharynx
- Middle constictor muscle is the thyopharyngeous muscle
- Origniates from the hyoid bone
- Caudal constictor muscles are the cricopharyngeous muscle
- Originates from the thyroid cartilage of the larynx
Muscles that dilate
- Enclose pharynx laterally and dorsally
- Dilator muscle is the stylopharyngeous muscle
- Originates from the hyoid apparatus
- Widens the rostral pharynx
Muscles that shorten
- The pterygopharyngeal muscle and palatopharyngeal muscle shorten the pharynx
- Enclose pharynx laterally and dorsally
Muscles that close the Pharyngeal Arch
- The palatopharyngeous muscle also closes the pharyngeal arch
Innervation
- Pharyngeal muscles arise from arch 4
- Stylopharyngeous muscle comes from arch 3 and is innervated by the accessory nerve (CN XI)
- Glossopharyngeal nerve (CN IX) supplies taste to the pharynx
Histology
- Fibroelastic aponeurosis supports the mucosa
- nasopharynx has pseudostratified columnar epithelium
- oropharynx and the laryngeal pharynx have stratified squamous epithelium
- oropharynx and the laryngeal pharynx have salivary glands present
Species Differences
Canine
- Single duct connects nasopharynx to the nasal cavity
- Tonsils are a compact mass which point away from the lumen of the pharynx
Equine
- Auditory tube opens into the guttural pouch
- Tonsils are diffuse and raised slightly
- Horses are unable to breath through the mouth as the free apex of the rostral epiglottis lies dorsal to the soft palate in a normal horse.
Ruminants
- Tonsils are a compact mass which point towards the lumen of the pharynx
Links
Oropharynx - Anatomy & Physiology