Organs - Nose and Sinuses Flashcards
What is the function of the nose?
1) Olfactory (smell)
2) Ventilation
What are the functions of the nasal cavity?
1) Warm and humidify the inspired air
2) Removes and traps pathogens and particulate matter from the inspired air.
3) Responsible for sense of smell.
4) Drains and clears the paranasal sinuses and lacrimal ducts.
What are the divisions of the nasal cavity?
The nasal cavity extends from the vestibule of the nose and the nasopharyx - it has three divisions:
1) Vestibule - the area surrounding the anterior external opening to the nasal cavity.
2) Respiratory region - lined by a ciliated pseudostratified epithelium, interspersed with mucus-secreting goblet cells.
3) Olfactory region - located at the apex of the nasal cavity. It is lined by olfactory cells with olfactory receptors.
What are the nasal conchae?
How many are there?
These are lateral curved shelves of bones, lined on the walls of the nasal cavity. These are conchae (or turbinates). The are three conchae - inferior, middle and superior.
They project into the nasal cavity, creating four pathways for the air to flow. These pathways are called meatuses.
Inferior meatus - between the inferior concha and floor and nasal cavity.
Middle meatus - between the inferior and middle concha.
Superior meatus - between the middle and superior concha.
Spheno-ethmoidal recess - superiorly and posteriorly to the superior concha.
Their function is to increase surface area of the nasal cavity. It also makes inspired air slower and more turbulent so that it can be humidified easier.
What are the openings into the nasal cavity?
One of the functions of the nose is to drain a variety of structures.
1) Paranasal sinuses (frontal, maxillary, anterior ethmoidal) open into the middle meatus. The location of this opening is marked by the semilunar hiatus, a crescent-shaped groove on the lateral walls of the nasal cavity.
2) The middle ethmoidal sinuses empty out onto a structure called the ethmoidal bulla. This is a bulge in the lateral wall formed by the middle ethmoidal sinus itself.
3) The posterior ethmoidal sinuses open out at the level of the superior meatus.
4) The sphenoid sinus drains onto the posterior roof.
5) Nasolacrimal duct - acts to drain tears from the eye. It opens into the inferior meatus.
6) Eustachian tube - opens into the nasopharyx at the level of the inferior meatus. It allows the middle ear to equalise with the atmospheric air pressure.
Clinical relevance: spread of infection
As the auditory tube (Eustachian tube) connects the middle ear and the upper respiratory tract, it is a path by which infection can spread from the upper respiratory tract to the ear. Infection of the auditory tube causes swelling of the mucous lining, and the tube becomes blocked. This results in diminished hearing.
What are the gateways to the nasal cavity?
1) Cribiform plate - this is part of the ethmoid bone - forms the roof of the nasal cavity. It contains very small perforations, allowing fibres of the olfactory nerve to enter and exit.
2) Sphenopalatine foramen - located at the level of the superior meatus - allows communication between the pterygopalatine fossa and the nasal cavity.
3) Incisive canal - pathway between the nasal cavity and the incisive fossa of the oral cavity. It transmits the nasopalatine nerve and the greater palatine artery.
What is the vasculature of the nose?
It has a very rich vascular supply to effectively change humidity and temperature of inspired air. The nose receives blood from both the internal and external carotid arteries:
Internal carotid branches:
- Anterior ethmoidal artery
- Posterior ethmoidal artery
The ethmoidal arteries are branch of the ophthalmic artery. They descend into the nasal cavity through the cribiform plate.
External carotid branches:
- Sphenopalatine artery
- Greater palatine artery
- Superior labial artery
- Lateral nasal arteries
These arteries also form anastomoses with each other - this is particularly prevalent in the anterior portion of the nose.
The veins of the nose tend to follow the arteries. They drain into the pterygoid plexus, facial vein or cavernous sinus.
In some individuals, a few nasal veins may join the saggital sinus - representing a potential pathway by which infection can spread from the nose into the cranial cavity.
Clinical relevance: epistaxis
Epistaxis is the medical term for nose bleed. Due to the rich blood supply of the nose, this is a common occurrence. It is most likely to occur in the anterior third of the nasal cavity - this area is known as the kiesselbach area.
The cause can be local (such as trauma) or systemic (such as hypertension).
What is the innervation of the nose?
The innervation of the nose can be functionally divided into special and general innervation.
Special (ability to smell) - olfactory nerves. The olfactory bulb, part of the brain, lies on the superior surface of the cribiform plate, above the nasal cavity. Branches of the olfactory nerve run through the cribiform plate to provide special sensorry innervation to the nose.
General -
Septum and lateral walls - nasopalatine nerve (a branch of the maxillary nerve) and the nasociliary nerve (a branch of the ophthalmic nerve).
External skin of the nose - trigeminal nerve
Clinical relevance: Cribiform plate fracture
A fracture of the cribiform plate can occur as a result of nose trauma. It is either fracatured directly by the trauma, or by fragments of the ethmoid bone.
A fractured cribiform plate can penetrate the meningeal linings of the brain, causing leakage of the CSF. Exposing the brain to the outside environment like this increases the risks of meningitis, encephalitis and cerebral abscesses.
The olfactory bulb lies on the cribiform plate and can be damaged irreversibly by the fracture. In this case, the patient may present with anosmia (loss of smell).
