This is not a treatise on human anatomy, but an attempt to diagram the anatomy of the nose and sinuses in order to understand the physiology and pathology of the region. 

1) The nose

• It is assimilated to an osteo-cartilaginous pyramid draped by a skin of variable thickness, lined by a more or less important muscular system. The base of this pyramid is formed by the nostril orifices
• Its location in the middle of the face exposes it to aesthetic evaluation, but also to trauma and sunlight.

a) The skin of the nose

• It varies in thickness from one region to another. Thin on the nasal bridge, thick at the tip of the nose, but with inter-individual variations.
• With exposure to the sun, the skin of the nose is subject to the appearance of skin cancers, which will sometimes require removal with reconstructions that must respect the aesthetic units of the nasal pyramid.
• ENT specialists share the competence of treating these lesions with dermatologists and plastic surgeons.

b) The nasal skeleton

          It is made up of two parts
 

1. a rigid, bony part, the bones of the nose, placed on the facial mass like a tent. These bones are relatively thin and fragile, exposed to trauma and fractures
2. a flexible cartilaginous part, the nasal tip, which supports the tip of the nose and contributes to its curvature.

The whole of this osteo-cartilaginous canopy (or tent) is supported by a septum which separates the 2 nasal cavities:
 

c) the septum, or nasal septum.

          This septum is also made up of cartilage at the front and bone at the back. The nasal septum is exceptionally planar and rectilinear; there is always a more or less significant deviation, linked to the stresses exerted on the cartilage by the growth of the bone and the cartilage itself.

But sometimes this deviation is significant and will cause breathing difficulties. Trauma also causes deviations that may need to be repaired.

 2) THE NASAL CAVITIES

The nasal cavities are two cavities located on either side of the nasal septum and which connect the outside with the rhinopharynx. They allow the passage of inspired air but have 3 other functions: 
 
- Warming the inspired air

- Humidifying the air

- The perception of odours.

Nasal breathing is the only physiological one, even if we can breathe through the mouth. Moreover, it is the location of the sensory cells of the sense of smell, which are involved in 90% of the perception of the taste of food. In fact, taste is very little provided by the tongue, which only perceives 4 flavours: salty, sweet, acidic and bitter. All the other flavours experienced when eating are due to "retro-olfaction", i.e. the passage of odorous molecules through the rhinopharynx to the nasal cavities.

 To ensure these functions, the nasal cavities are covered by a respiratory mucosa, permanently humidified by specialised cells. This mucous membrane covers bony reliefs on the outer wall of the nasal cavities: the turbinates.

a) The turbinate

are bony formations, rolled up on themselves, in the shape of a horn, hence their name, and covered by an erectile mucosa which swells alternately on one side and then on the other every 3 to 5 hours: this is called the nasal cycle

This explains why, in general, the two nasal cavities are not open in the same way at a given moment, but that this changes over time. In the event of a disturbance of this system (cold, allergy, dysfunction of the nasal cycle) the two nasal cavities can become blocked at the same time, leading to an obstruction of the nose and a discharge.

There are 3 turbinates on each side: 

      - the lower turbinate,

      - the middle turbinate

      - and the upper turbinate.

They are separated from each other by spaces called meatus.

b) Meatus

The meatus are the spaces between two turbinates. We can distinguish

- the inferior meatus located under the inferior turbinate, its only interest lies in the fact that it receives the lacrimal duct allowing the drainage of tears in the nose. It can also be a surgical approach to the maxillary sinus

- the middle meatus, located between the inferior and middle turbinates. It is of major interest because it is the drainage site of all the anterior sinuses of the face: the maxillary sinus, the frontal sinus and the anterior part of the ethmoidal sinus. It is at this level that the surgical treatment will be the most physiological.

- the superior meatus located between the middle and superior horns, which drains the posterior sinuses of the face: the posterior part of the ethmoidal sinus and the sphenoidal sinus

3) THE SINUSES

The sinuses are air cavities formed in the facial mass, covered by respiratory mucous membrane, and connected to the nasal cavities by a drainage orifice which ends at the meatus.

A distinction is made between

1) the anterior sinuses, which drain into the middle meatus and which are from top to bottom

the frontal sinuses
the ethmoidal sinuses (anterior part)
the maxillary sinuses
 

2) and the posterior sinuses which are from front to back (image of a CT scan in horizontal section passing through the eyes)

The ethmoidal sinuses (posterior part)
The sphenoidal sinuses
 

- Indeed, an affection concerning only the anterior sinuses, especially if it is unilateral, is the witness of an exclusively local problem: either an infection of dental origin, or an obstruction of the middle meatus by an oedema, an inflammation, a tumour (rarely). Similarly, there may be exclusive involvement of the posterior sinuses (rarer), which should lead to an obstruction of the sinus drainage orifice.

        - On the other hand, a condition affecting the anterior AND posterior sinuses, especially if it is bilateral, indicates that there is a general pathology of the respiratory mucosa, and should therefore be treated as a whole, with surgery only in the case of failure of medical treatment, and only when nasal obstruction is the patient's main complaint.

Their physiological role is still uncertain: they could by their presence reduce the weight of the head, which would be heavier if all the bones were full. But there are other theories.

Here it is necessary to specify a physiological particularity of the respiratory mucosa:

when we breathe, the dust inhaled through the nose sticks to the mucus naturally secreted by the respiratory mucosa. This mucus is permanently transported, thanks to the ciliary movements, TO THE BACK OF THE NASAL TANKS: it is thus natural to have secretions which "go down" in the throat to be DEGLUED (see diagram below). These secretions do not actually go into the bronchi.

As a corollary, the same phenomenon occurs in the trachea and bronchi: there is a "conveyor belt" of mucus on which the breathed-in "dust" has stuck, which brings all the secretions up to the larynx. At the level of the vocal cords there is no more conveyor belt, so a throat "clearing" is necessary to expel this mucus which will then be swallowed.

So we must get rid of this expression, which is rooted in the collective imagination: "Doctor, I have secretions falling into my bronchi". On the other hand, the respiratory mucous membrane that lines the entire respiratory tree "from the sinuses to the bronchi" can be the object of viral infections most often, and sometimes bacterial ones, which spread throughout the mucous membrane. And that's another story...

to talk about sinuses again: Any change in aeration, drainage, mucus quality, or ciliary transport can lead to inflammation or infection of the sinus.

On the other hand, the maxillary sinuses are closely connected with the base of the teeth, and an infection of the teeth can spread to the sinus.