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Equine Upper Respiratory Tract - Horse Anatomy (view source)
Revision as of 16:36, 18 November 2012
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==Nose==
==Nose==
The nares are supported by nasal cartilages. Unlike other species the ventral and dorsal lateral nasal cartilages, which attach to the rostral end of the nasal septum, do not contact each other. In the hose, the dorsal and ventral cartilages are indistinct or absent. Instead, horses have '''alar cartilages''' to support the nostrils, but the lateral walls of the nostrils remain unsupported; allowing greater mobility. The alar cartilages divide the nostril into the dorsal ('false nostril') and ventral ('true nostril'). The dorsal nostril leads to a blind-ending diverticulum in the nasoincisive notch. The ventral nostril leads to the nasal cavity. This is important when placing a nasogastric tube, which must be inserted ventrally.
The nares are supported by '''nasal cartilages'''. Unlike other species the ventral and dorsal lateral nasal cartilages, which attach to the rostral end of the nasal septum, do not contact each other. In the hose, the dorsal and ventral cartilages are indistinct or absent. Instead, horses have '''alar cartilages''' to support the nostrils, but the lateral walls of the nostrils remain unsupported; allowing greater mobility. The alar cartilages divide the nostril into the dorsal ('false nostril') and ventral ('true nostril'). The dorsal nostril leads to a blind-ending diverticulum in the nasoincisive notch. The ventral nostril leads to the nasal cavity. This is important when placing a nasogastric tube, which must be inserted ventrally.
Another species difference is that the nasolacrimal duct opens at the nasal puncta on the ventral floor of the nasal vestibule close to the transition point between the nasal mucosa and the nostril.
Another species difference is that the nasolacrimal duct opens at the nasal puncta on the ventral floor of the nasal vestibule close to the transition point between the nasal mucosa and the nostril.
Horses do not have a nasal philtrum.
==Nasal Cavity==
==Nasal Cavity==
The nasal cavity is the area between the nostrils and the cribiform plate, it is divided by a septum into right and left sides. The '''nasal conchae''' (ethmoid turbinates) are scroll-shaped bones covered with nasal mucosa that project into the nasal cavity. The first endoturbinate is the base of the dorsal nasal conchae. It extends the furthest into the nasal cavity. The second endoturbinate forms the middle nasal concha. Subsequent turbinates are much smaller. The ventral nasal conchus is not formed by turbinates, but by the maxilla.
The nasal cavity is the area between the nostrils and the cribiform plate, it is divided by a septum into right and left sides. The '''nasal conchae''', also known as ethmoturbinate, are scroll-shaped bones covered with nasal mucosa that project into the nasal cavity. The first endoturbinate is the base of the dorsal nasal conchae. It extends the furthest into the nasal cavity. The second endoturbinate forms the middle nasal concha. Subsequent turbinates are much smaller. The ventral nasal conchus is not formed by turbinates, but by the maxilla.
The conchae divide the nasal cavity into three meatuses, which form a common meatus near the nasal septum.
The conchae divide the nasal cavity into three meatuses, which form a common meatus near the nasal septum.
*Dorsal nasal meatus: Between the dorsal nasal meatus and the dorsal concha. It leads directly to the nasal cavity.
*Dorsal nasal meatus: Between the dorsal nasal meatus and the dorsal concha. It leads directly to the caudal nasal cavity.
*Middle nasal meatus: Between the dorsal and ventral nasal conchae, communicates with paranasal sinuses.
*Middle nasal meatus: Between the dorsal and ventral nasal conchae, communicates with paranasal sinuses and leads into the caudal nasal cavity.
*Ventral nasal meatus: Between the floor of the nasal cavity and the ventral nasal concha. This is the main passage of airflow to the nasal cavity.
*Ventral nasal meatus: Between the floor of the nasal cavity and the ventral nasal concha. This is the largest meatus and is the main passage of airflow to the nasal cavity via the nasopharynx. Nasogastric tubes, passed through the nasal cavity, pharynx and oesophagus to the stomach, must be passed through this meatus to avoid the highly vascularised ethmoturbinates.
*Common nasal meatus: Either side of the nasal septum, communicates with all other meatus.
*Common nasal meatus: Either side of the nasal septum, communicates with all other meatus.
==Paranasal Sinuses==
==Paranasal Sinuses==
==Pharynx==
==Pharynx==
The three parts of the pharynx are the '''oropharynx''', '''laryngopharynx''' and '''nasal pharynx'''. The '''[[Soft Palate|soft palate]]''' separates the rostral part of the pharynx into the nasopharynx (dorsal) and oropharynx (ventral). The laryngopharynx is where these two compartments communicate, located in the caudal part of the pharynx.
*Oropharynx: Extends from the glossopalatine arch in the oral cavity to the base of the epiglottis.
*Nasopharynx: Forms part of the ventral nasal meatus through the choanae. It communicates with the ostia of the auditory tubes, auditory tubes and the guttural pouch.
*Laryngopharynx: Extends from the intrapharangeal opening to the oesophagus and the larynx.
During normal breathing, the [[Soft Palate|soft palate]] extends to the base of the epiglottis. The free apex of the rostral epiglottis lies dorsal to the [[Soft Palate|soft palate]]. This means horses are obligate nasal breathers and are unable to vomit. If horses do vomit, it is expelled through the nose.
===Pharyngeal Muscles===
The muscles are the ''tensor veli palatine'' and ''levator veli palatine''. The rostral pharyngeal constrictors are ''pterygopharyngeus'' and ''palatopharyngeus'', which arise from the base of the skull. The caudal pharyngeal constrictors are the ''thyropharyngeus'' and ''cricopharyngeaus'', which arise from the larynx. The only dilator of the pharynx is the ''stylopharyngeus caudalis''.
===Innervation===
The nervous supply comes from the pharyngeal branch of the vagus nerve ([[Cranial Nerves - Anatomy & Physiology|CN X]]) and from the cranial root of the accessory nerve ([[Cranial Nerves - Anatomy & Physiology|CN XI]]). The stylopharyngeous muscle is innervated by the accessory nerve ([[Cranial Nerves - Anatomy & Physiology|CN XI]]). The glossopharyngeal nerve ([[Cranial Nerves - Anatomy & Physiology|CN IX]]) supplies taste to the pharynx.
==Trachea==
==Trachea==
The trachea begins at the larynx and ends at the hilus, where it divides into the left and right mainstem bronchi. The average length of the trachea in horses is 75-85cm and diameter is 5-6cm. It is comprised of 50-60 cartilagenous rings, which are incomplete dorsally. Between each ring is a '''tracheal annular ligament'''. The '''dorsal tracheal membrane''' lies on the inner surface of the cartilages and is composed of smooth muscle, mucosa and adventitia. Most of the trachea is cylindrical in shape, but the cervical part is flattened dorsally due to contact with the ‘’longus colli’’ muscle.
==References==
==References==
[[Category:To Do - AP Review]]
[[Category:Horse Anatomy]]
[[Category:Horse Anatomy]]