Sinus Anatomy and Histology


External Nose:

the external nose – the part of the nose that you see – is there for more than just to make you or your child beautiful. Those cartilage and bone structures are there to keep the nasal airway open. Think of the boxer with the pulverized nose who can no longer breathe through his nose. Anyone who has ever broken their nose – elbow during basketball, softball to the nose, whatever – knows that having those structures intact helps keep your nose open, helps keep your breathing clear, open and smooth.

Nasal Cavities:

where all the action takes place, your nose functions as:

  • air conditioner – humidification, warming or cooling incoming airstream
  • filter the incoming airstream of microorganisms and pollutants
  • immune function – preventing infection by airborne microorganisms
  • olfaction – sense of smell
  • voice quality – affects voice resonance

Nasal Septum: divides the nose into right and left halves. If the nasal septum is deviated (born like that or acquired from trauma), obstruction can result. If severe enough, septal deviation may warrant surgery (septoplasty) to improve nasal airway.


3 swellings along the side wall of the nasal cavity. Their function:

  • create turbulent airflow – this aides in sense of smell, and helps mucus trap microorganisms and pollutants in the airstream (a good thing)
  • cover the openings to the paranasal sinuses (why, we don’t know)
  • alter voice resonance? (we’re pretty much speculating here)


The Adenoids lie in the nasopharynx at the very back of the nose. The adenoid tissue is lymphoid tissue. It looks well, pretty gross. It is involved in killing microorganisms that are captured by the nasal secretions. Those secretions are swept to the back of the lose by cilia motion. This is the area where the nose, sinuses, adenoids and tonsils, and the openings to the Eustachian tubes (to the middle ears), all connect.

Therefore, in a way, the adenoids are sort of a key to keeping everything here (nose, sinuses, eustachian tube and middle ears) healthy. Unhealthy adenoids – acute or chronic adenoiditis – can be a cause of major nose, sinus, and ear problems.

If you look at the picture below, taken through the mouth using an angled endoscope, looking forward toward the front of the nose, the top of the palate is at the bottom, you can see the nasal septum in the middle, the nasal turbinates attached to either side of the nose, the Eustachian tube opening on the right side is visible (there is one on the left also), and the adenoids at the top of it all.

If the adenoids are too big, they can block the nose – nasal obstruction. The result is difficulty breathing through the nose, and probable rhinitis and sinusitis.

Paranasal Sinuses:

air-filled cavities within the bones of the face, connected to the nasal cavities. There is great variation in sinus shape and size between people. Have uncertain role; some speculate that they help lighten the facial skeleton, sort of like hollow bird bones make them lighter.

The sinuses consist of four paired cavities each of which is named after the bone in which it is located. The four sinus pairs:

  • the Maxillary sinuses – in bones of cheeks, one on each side. May grow to be as large as 15ml (could hold about 3 tablespoons).
  • the Ethmoid sinuses – usually 6 – 10 per side, situated between the orbits (eye sockets), up to the skull base. Responsible for more complications from sinusitis than other sinuses, usually involving the orbits (eye sockets) and tissues around the eyes. The Ethmoid sinuses are small and irregular, sort of like the “nooks and crannies” that you see when you cut open an English muffin.
  • the Sphenoid sinuses – 1 or 2 lie in the very middle of the head, surrounded by the pituitary (part of the brain), optic nerves (from the eyes), internal carotid arteries – all important structures. Rarely a source of sinusitis complications, but due to location, complications can be life-threatening (meningitis, brain abscess).
  • the Frontal sinuses – situated in the eyebrow area of forehead bone of the skull. Usually one each side, but one or both are absent in about 5% of us. Due to the fact that the brain is just behind the frontal bones, sinusitis complications in the frontal sinuses can be serious (meningitis, brain abscess); fortunately this is rare.


The lining of the nose is our first line of defense against airborne microorganisms and pollutants. This task is handled by the epithelium through mucociliary clearance (more detail about this in another post). The nasal epithelium functions to:

  • Acts as a physical barrier to inhaled foreign materials
  • Entraps and clears foreign material by…
  • Mucus secretion (snot) and
  • Cilia activity
  • Is an active part of our immune response – contains enzymes and antibodies
  • Helps condition the air we breathe in: warm it, cool it, moisturize it

Nasal (and sinus) epithelium: is comprised of

  • cells with cilia
  • cells without cilia
  • goblet cells, and
  • basal cells
  • transient immune cells – lymphocytes and mast cells

The ciliated and non-ciliated cells help create most of the physical barrier as they form a tightly-connected sheet that lines the nasal cavity. This “tight junction” that is formed between these cells, effectively keeps foreign materials – pollutants and microorganisms- from getting into our tissues and bloodstreams. A breakdown in this barrier can be dangerous.

The goblet cells produce mucus – snot. Nasal mucus, in the proper viscosity (thickness, stickiness) and amount, is the key to the system of mucociliary clearance working normally. Mucociliary clearance is the holy grail for healthy sinuses. Achieve this, you achieve respiratory health.


The most important feature of the respiratory epithelium, are the cilia.

Cilia of the ciliated epithelial cells work together to sweep out the mucus that contains any adherent foreign material, including microorganisms and pollutants.

In order to work normally, these cilia need a certain level of humidity. They are also VERY sensitive to airborne pollutants. These include toxins that are in cigarette smoke, in common air pollution, and various volatile organic compounds (VOC’s). VOC’s are all around us in our synthesized, plasticized, man-made world. They come out of our cleaning agents, out of adhesives, and out of all that plastic. These toxins prevent the cilia from working properly.

If mucociliary clearance does not function, we can expect chronic respiratory illness, and life-threatening infections can result. These cilia are on the respiratory epithelial cells that line the upper and lower respiratory tract, including the nose, the sinuses, and the middle ear, as well as the trachea and bronchioles. So, if they don’t keep these areas swept clean, the result can be infections in those areas: rhinitis, sinusitis, otitis (ear infections), bronchitis, and pneumonia.

The basal cells are progenitor cells – baby cells – that will divide and grow to replace the other cell types when they grow old or are lost due to a toxic environment. The immune response of the nasal epithelium helps us fight off attacks from various microorganisms (viruses, bacteria, mold), but if it goes haywire, can contribute to allergic rhinitis.

Immune Function:

Finally, the mucus contains special antibodies and enzymes that:

  • prevent viruses and bacteria from sticking to the epithelial lining
  • help our white blood cells to recognize viruses and bacteria as invaders and to kill them

Sorry for the dry, boring anatomy lesson, but it is important to have some idea of how the sinuses relate to the nose and rest of the upper airway, how it all fits together and how it works, if we are to succeed at keeping it all healthy. Thanks for visiting.