Anatomy Basics
Nasal Cavity
When air enters the nostrils, it passes through the vestibule which is lined by skin containing coarse hairs that filter out large dust particles and prevents dehydration by trapping water droplets during exhalation. The horse is an obligate nasal breather. Collapse of the nostrils is prevented by the alar cartilage on the medial aspect. The soft lateral aspect of the nostril allows for dilation to occur when breathing rate is increased. Inhaled air enters the nasal cavity and is warmed by blood circulating in the capillaries. Mucus is secreted by the goblet cells and moistens the air and traps dust particles. Cilia move the mucus and trapped dust particles toward the pharynx where they can be swallowed or spit out. The olfactory receptors lie in a region of the membrane lining called the olfactory epithelium. The horse's receptors are located in the mucosa of the upper nasal cavity. Due to the length of the nasal cavity, there is a large area of these receptors, and the horse has a better ability to smell than a human. The nasal cavity contains the turbinate bones, the sinuses and the meatuses. The hard & soft palates separate the nasal cavity from the oral cavity below. The nasolacrimal duct empties into the vestibule. The nasal cavity leads into the throat via the internal nares of chonae.
Pharynx
This is the throat, which starts at the internal nares and extends to the cricoid cartilage (the inferior cartilage of the larynx). It receives the warmed, moist air and is also lined with a mucus membrane. The pharynx functions as a passageway for air and food, provides a resonating chamber for sounds, and houses the lymph follicles. There are 3 anatomical regions:
1) Nasopharynx
Posterior to the nasal cavity extending to the soft palate Passage for air from nasal cavity to trachea
2) Oropharynx
Posterior to the oral cavity from soft palate to the hyoid bone. Passageway for food and drink from oral cavity to esophagus
3) Laryngopharynx (AKA Hypopharynx)
Posterior to the oropharynx, begins at the hyoid bone and opens into the esophagus. Functions in digestive processes
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