Upper respiratory tract

• Nostrils - species adaptations

  
  

  the entrance to nasal cavities

  supported by alar cartilage (elastic)

  • Nasal plate/philtrum -> carnivores
  • Nasolabial plate -> cow
  • False nostril -> horse
  • Os rostrale -> pig
• Alar cartilage in horse


  Large comma-shaped nostrils supported by extensive alar cartilage

  nostril divides into :

  • ventral -> true nostril leads to nasal cavity
  • dorsal -> false nostril (nasal diverticulum), leads to skin pouch

  *nasogastric tube via true nostril
• Brachycephalic dogs

  
  

  Airway abnormalities:

  • Narrow or slit-like nostrils (nostril goes inside nasal cavity)
  • Elongated soft palate (nasopharynx narrow)
  • Narrowing of trachea
  • Can lead to BOAS (brachycephalic obstructive airway syndrome)

  Labrador -> Mesocephalic (normal)

  Greyhound -> Dolichocephalic (long head)

  Pug -> Brachycephalic (short head)
• Nasal Cavities

  • extend to nasopharynx + enters via choana
  • nasal cavities filled with conchae -> scrolls of bone, covered with ciliated mucosa
  • 3 conchae -> dorsal, ventral and ethmoconchae (olfaction)
• Function of conchae


  Help in directing and filtering airflow in the nasal cavity *
• Nasal meatuses - connects to paranasal sinuses

  • Dorsal
  • Middle
  • Ventral
  • Common
• Ventral meatus

  Leads to pharynx
• In horses, a nasogastric tube can be passed via :

  true nostril -> ventral meatus -> nasopharynx -> laryngopharynx -> oesophagus
• Where nasal meatuses lead to

  • Dorsal - frontal sinus (not in horse)
  • Middle - ethmoconchae and maxillary sinus
  • Ventral - nasopharynx to larynx and lower respiratory tract (and oesophagus)
• Equine paranasal sinuses

  • Frontal sinus
  • Rostral maxillary sinus
  • Caudal maxillary sinus
  • Sphenopalatine
  • Ethmoidal

  Important clinically -> =

  • associated with root of cheek teeth
  • problems with drainage
  • susceptible to infection
• Equine frontal sinus

  • communicates with the caudal aspect of dorsal concha, known as the conchofrontal sinus
  • drains indirectly to nasal cavity via caudal maxillary sinus
• Equine rostral and caudal maxillary sinuses


  1. Caudal maxillary sinus extends into splenopalatine sinus

  2. SP sinus and frontal/conchofrontal sinuses drain to caudal maxillary sinus
• Equine paranasal sinuses


  1. Extent of sinuses can vary: as teeth are extruded, with age

  2. Surgical access may be required to drain infection – trephination

  3. Important to consider position of sinuses during humane destruction
• Ruminant paranasal sinuses

  1. Maxillary sinus occupies large proportion of upper jaw

  2. Extends into other less important sinuses
• Equine rostral and caudal maxillary sinuses

  • compartments separated by bony septum
  • do not communicate with each other
  • relation to roots of cheek teeth
  • both incompletely divided into medial and lateral compartments by longitudinal bony plate
  • both drain into middle meatus and nasal cavity via common nasomaxillary opening
  • dorsal location of opening hinders drainage
  • rostral maxillary sinus extends into ventral concha
  • caudal maxillary sinus extends into splenopalatine sinus. SP sinus and frontal/conchofrontal sinuses drain to caudal maxillary sinus
• Maxillary sinus in ruminents

  • Occupies large proportion of upper jaw
  • Extends into other less important sinuses
• Frontal sinus in ruminants

  • 2-3 small rostral compartments and large caudal one
  • Left and right caudal compartments separated by thick midline septum – care needed to avoid this during humane destruction
  • In horned animals, caudal compartment extends dorsally into cornual process. When dehorning older calves, sinus can be opened – risk of infection
• Hyoid apparatus:

  Series of five small bones

  • Stylohyoid (paired)
  • Epihyoid (paired)
  • Ceratohyoid (paired)
  • Basihyoid
  • Thyrohyoid (paired)
• Stylohyoid bone attaches to skull via tympanohyoid cartilage
• Suspends larynx and tongue from skull
• Pulls larynx rostrally during swallowing to prevent food entering larynx/trachea
• Basihyoid bone in horse (and cow) has lingual process to help support tongue
• Stylohyoid bone greatly expanded, Epihyoid reduced
• Canine larynx: location and functions - Situated ventral & caudal to pharynx and cranial to start of trachea
• Hyoid apparatus suspends larynx and helps draw it rostrally during swallowing
• Functions of the canine larynx: Regulates entry of air into trachea, Vocalisation (production of voice), Epiglottis prevents food entry into trachea during swallowing (closes airway)
• Larynx: Four main cartilages - Epiglottis (elastic cartilage), Thyroid (hyaline cartilage), Arytenoid (hyaline, paired), Cricoid (hyaline)
• Species differences in shape of cartilage pieces
• We will concentrate on dog and horse trachea, epiglottis, thyroid, cricoid, arytenoid (paired)
• Canine laryngeal cartilages and articulations

  • Epiglottis
  • Thyroid cartilage
  • Arytenoid cartilages
  • Cricoid cartilage
  • Rostral cornu
  • Caudal cornu
  • Vocal process
  • Corniculate process
  • Cuneiform process
  • Muscular process
• Laryngeal cartilages


  Species differences: Canine, Equine
• Epiglottic cartilage (epiglottis)


  Canine: Most rostral, Consists of small stalk and leaf-like blade
• Arytenoid cartilage


  Canine: Pyramidal shaped, Contains vocal, muscular, and corniculate processes
• Thyroid cartilage


  Canine: Largest cartilage, Trough-shaped, Deep ventral notch in horse and caudally cricothyroid ligament
• Cricoid cartilage


  Canine: Signet ring-shaped, Most caudal
• Epiglottis in the horse is located behind the soft palate - retrovelar
• Horses are obligate nasal breathers
• Equine larynx regions


  • Aditus laryngis
  • Vestibule/supraglottic cavity
  • Glottic cleft (rima glottidis; glottis)
  • Infraglottic cavity
• Vocal fold vibrates


  Produces vocalisation
• Equine larynx folds and ventricles

  • Aryepiglottic folds
  • Vocal fold
  • Ventricular (vestibular) fold
  • Laryngeal ventricle