QS Study

Paranasal Air Sinuses

The paranasal air sinuses are the air-filled spaces present within bones around the nasal cavities. These sinuses are formed in childhood by the nasal cavity eroding into surrounding bone. They have several functions which reduce the weight of the head is the most important.

There are four paired sinuses, the sinuses are –

  1. Frontal air sinus – They drain into the nasal cavity via the frontonasal duct, which opens out at the hiatus semilunaris on the lateral wall.
  2. Maxillary air sinus – It is located laterally and slightly inferiorly to the nasal cavities. It drains into the nasal cavity at the hiatus semilunaris, underneath the frontal sinus opening.
  3. Sphenoidal air sinus – They are found more posteriorly, and are related superiorly and laterally to the cranial cavity. They drain out onto the roof of the nasal cavity.
  4. Ethmoidal air sinuses – They arise in the ethmoid bone, forming several distinct air cells between the eyes.

The sinuses are rudimentary, or even absent at birth. They enlarge rapidly during the ages of 6 to 7 years and then after puberty. From birth to adult life the growth of the sinuses is due to the enlargement of the bones and in old age, it is due to the resorption of the surrounding cancellous bone. The maxillary sinus is the first paranasal sinus to develop.

Paranasal Air Sinuses 1

Fig: Paranasal Air Sinuses

Functions – The function of the sinuses is not clear. It is thought that they may contribute to the humidifying of the inspired air. They also reduce the weight of the skull.

  • They make the skull lighter, so the overall weight of the head and neck lows down.
  • They add resonance to the voice, so consonants can be properly spelled.
  • Maxillary sinus bears sockets for the teeth of the upper jaw.
  • They give a good shape to the face.
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