Functions of Paranasal sinuses
The following are the possiblefunctions of paranasal sinuses:
Imparting resonance to the voice: Bartholinus in 17th century proposed that the paranasal sinusesplayed a viral role in resonation of spoken words. Howell studiedMaori people of New Zealand and attributed their dead voices to theirpoorly developed paranasal sinuses. Proetz questioned this theorysaying that Lions which had huge roars had small sinuses. He alsowent on to suggest that Guinea pig and Giraffes which had feeblevoices had well developed sinus cavities. Negus demonstrated through hiscomparative study that presence or absence of sinuses had no role toplay in determining the quality of voice.
Humidification & warming ofinspired air: Air exchange is known to take place inside paranasalsinuses during respiration. The quantum of exchange is of coursenegligible. Since the quantum of air exchange has found to benegligible, it is unlikely for significant amount of humidificationoccurring inside the sinuses. It has been experimentallydemonstrated that even after full 5 mins of respiration, air insidethe maxillary sinus cavities are not exchanged at all.
Increasing the olfactory area ofnose: Cloquet in 1930 proposed that human maxillary sinus mucosa isof olfactory sensory epithelium type. He also presumed that themucosal lining of paranasal sinuses increased the surface area ofolfactory epithelium. This surmise of course is false given the typeof epithelial lining of maxillary sinuses.
Providing thermal insulation tovital parts of head: It was proposed by Proetz that sinusesfunctioned as thermal insulators much like the water jacket ofinternal combustion engine. It has been observed that Eskimos don’thave frontal sinuses while Africans have large frontal sinuses. These facts go on to prove that thermal insulation could not be theonly function of paranasal sinuses.
Shock absorber function: Negusproposed that paranasal sinuses could play a role in absorbing shockand protecting the sense organs from the effects of shock. Blaneyshowed that species more prone to injuries to critical sense organshad relatively small paranasal sinuses thus making this theoryredundant.
Aiding facial growth: Proetzproposed that the human frontal and maxillary sinuses were designedto assist forward and downward growth of the face. To substantiatethis theory he pointed out that frontal sinuses develop along withadvancement of the face, while the maxillary sinuses develop with thegrowth of jaw and sphenoid. Negus rejected this theory pointing outpatients with deficient / poorly developed frontal sinuses had normalfacial skeletal growth.
Eckel’s theory: Eckel surmisedthat it was bite and chewing functions that determined the size ofmaxillary sinuses.
Evolutionary remnants: Negusconcluded that there is no functional reason to account for thepresence of paranasal sinuses. He stated that “we possess theparanasal sinuses because our ancestors did”.
Lightening the skull bones tomaintain head position: This theory suggests that paranasal sinusesreduced the weight of the skull. Studies involving the neckmusculature suggest that the presence of sinuses don’t reduce theweight of skull significantly.
Floatation device: Hardy and Evan’ssuggested that paranasal sinuses could act like a floatation device. This helps in maintaining the nose above the level of water whileswimming.
Secreting mucous to moisten thenasal cavity: Haller suggested that paranasal sinuses played animportant role by moistening the nasal cavity mucosa. This hashowever been found to be untrue since the mucosal glands in themaxillary sinus is very little when compared to that of nasal mucosa.
Aiding nasal cavity immune defenseand production of nitric oxide: Sinuses play a vital role in aidingthe immunological function of the nasal mucosa. Nitric oxide hasbeen found to be generated by mucosa of paranasal sinuses in verylarge quantities. Nitric oxide has been postulated to have anantiviral and bacteriostatic function. It also upregulates theciliary beat frequency.