Paranasal Sinuses - Anatomy & Physiology
Introduction
The paranasal sinuses are ventilated spaces connected to the nasal cavity. They develop as blind ending pouches between the lamina of the bones of the skull.
Structure
The paranasal sinuses are a series of cavities arranged one after another. All species have frontal and maxillary systems.
Frontal: Consists of space(s) within the bones between the cranial cavity and the nasal cavity.
Maxillary: This is the largest sinus, and consists of the space within the caudolateral part of the upper jaw, above the caudal cheek teeth. This increases with age due to wearing and ventral relocation of the teeth.
Function
The function of paranasal sinuses is somewhat ambiguous, however they are likely to have the following evolutionary purposes:
- Resonating cavities
- Limiting the weight of the skull
- Insulation/cooling of the brain
- Increased insertion space for teeth
Species Differences
In the dog the sinus system is generally poorly developed. The maxillary sinus is a cavity which freely communicates with the nasal cavity, and is known as the maxillary recess. The frontal sinus has 3 chambers which drain separately into the nasal cavity.
In the horse the maxillary sinus has caudal and rostral parts which together occupy a large part of the upper jaw. In addition, the horse has sphenopalatine and ethmoidal sinuses which are of a lesser clinical importance than the frontal, caudal maxillary and rostral maxillary sinuses on each side of the skull.
Cattle do not have a fully developed sinus system until the age of 7, by which time it is an extremely complex system. In addition to the frontal sinus, there is a palatomaxillary sinus (named because the maxillary sinus is continuous with the palatine sinus) within the caudal part of the hard palate and face, a lacrimal sinus within the medial orbit, sphenoidal sinuses which lie past the orbit and within the conchae themselves are the conchal sinuses. The frontal sinus in cattle has a 'diverticle' for the cornual process (horn).
The pig has lacrimal, sphenoid and conchal sinuses in addition to the maxillary and frontal systems.
There are many variations to the entire avian respiratory tract.
The respiratory systems of non-homeotherms are also very different to that of mammals.
Links
Click here for more information on paranasal sinuses pathology.
References
Dyce, K.M., Sack, W.O. and Wensing, C.J.G. (2002) Textbook of Veterinary Anatomy. 3rd ed. Philadelphia: Saunders.
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