Next Lesson - The Oral Cavity and Pharynx
Core
The nose is the uppermost part of the respiratory tract (the airways) and lies immediately superior to the hard palate (the bony roof of the mouth).
Functions of the nose include:
- Olfaction (smell)
- Conduction of inspired air
- Filtration of inspired air
- Humidification and warming of inspired air
- Resonance chamber for speech
- Drainage of secretions from the paranasal sinuses and nasolacrimal ducts (the tubes that drain tears from the eyes into the nose)
The external nose is the visible portion of the nose which protrudes from the face. Its prominent nature makes it particularly easy to injure in facial trauma (injury).
The nose has two external openings called the nares (or nostrils). Via the nares, inspired air immediately enters the vestibule of the nose (the entrance chamber just inside the nostril). The vestibule is lined with skin containing sebaceous glands (oil-producing glands) and hairs. The hairs assist in trapping unwanted particles from the air.
The skeleton of the nose is predominantly hyaline cartilage with a proximal bony root.
The bony part of the nose consists of the nasal bones, frontal processes (bony projections) of the maxillae, nasal part of the frontal bone and the bony part of the nasal septum.
There are 5 main nasal cartilages (a few smaller alar cartilages are also present):
- 2 Lateral Cartilages - situated just inferior to the nasal bones. They are flattened and triangular in shape.
- 2 Alar Cartilages (alar means wing-shaped) - the soft, flexible part of the external nose. These cartilages are mobile and can dilate with contraction of the nasalis muscle.
- 1 Septal Cartilage - the cartilaginous part of the nasal septum.
Diagram - The nasal skeleton
Creative commons source by OpenStax College, edited by Dr. Joshua Bray [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
The nasal cavity is the internal space of the nose, which extends from the vestibule to the nasopharynx (the part of the throat behind the nose). It lies in an approximately horizontal plane.
The boundaries of the nasal cavity are:
- Roof - cribriform plate of the ethmoid (the thin, perforated part of the ethmoid bone that the nerves of smell pass through), with contributions from the nasal bone anteriorly
- Floor - hard palate
- Lateral Walls - maxilla (mainly)
- Medial Wall - nasal septum
The nasal septum separates the left and right nasal cavities. It has 2 parts:
- Cartilaginous (anteriorly)
- Bony (posteriorly) - consisting of the perpendicular portion of the ethmoid bone and the vomer bone (a thin, flat bone forming the lower back part of the septum)
Diagram - The nasal septum
Creative commons source by OpenStax College [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
Trauma to the nose could shear blood vessels in the nasal septum, causing a septal haematoma. This haematoma separates the cartilage from its overlying perichondrium (the membrane that covers cartilage and supplies it with blood), depriving the cartilage of its blood supply. If left untreated, the septal cartilage undergoes avascular necrosis (tissue death from loss of blood supply) and remodelling, resulting in a saddle-nose deformity (the bridge of the nose collapses inwards). The collection of blood can also become infected (a septal abscess), which can destroy the cartilage, make a hole in the septum (perforation) and lead to serious complications, including infection inside the skull. A septal haematoma is therefore an emergency and needs urgent drainage by a specialist in ear, nose and throat (ENT) surgery.
The nasal cavity is lined with mucosa and is highly vascular.
The olfactory mucosa lines the roof of the nasal cavity and houses olfactory neurones, which are responsible for our sense of smell. The neurones respond to chemicals in the air (aromas) by producing action potentials. These signals travel along the olfactory nerve (cranial nerve I, or CN I).
The rest of the nasal cavity is lined with respiratory mucosa. The respiratory mucosa is composed of pseudostratified columnar epithelium (tall cells in a single layer that looks layered) and houses cilia (tiny hair-like projections that sweep mucus along) and mucous glands. It acts to warm, humidify and filter inspired air.
The nasal conchae (or turbinates) are bony shelf-like projections from the lateral walls of the nasal cavity. There are 3 pairs of conchae: superior, middle and inferior. Each concha has a respective meatus, which is a gap underneath the curve of the concha. The function of the conchae is to induce turbulent air flow, thereby slowing air flow and increasing the opportunity for humidification and warming.
Diagram - The nasal cavity and conchae
Public Domain Source (NIH) [Public domain]
The paranasal sinuses are air-filled extensions of the nasal cavity. They are lined with respiratory mucosa. Their function is still debated. Suggested roles include lightening the weight of the head, supporting immune defence of the nasal cavity, humidifying inspired air and adding resonance to the voice.
There are 4 pairs of sinuses:
- Frontal - situated between the outer and inner layers (tables) of the frontal bone.
- Ethmoidal - otherwise termed ‘ethmoidal air cells’. They are small invaginations (inward pockets) of mucosa into the ethmoid bone (the bone between the eyes).
- Maxillary - the largest of the paranasal sinuses, located within the body of the maxilla, just inferior to the orbit (eye socket).
- Sphenoidal - located within the body of the sphenoid bone (the central bone at the base of the skull).
Diagram - Paranasal air sinuses
Creative commons source by OpenStax College [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
The paranasal sinuses have important anatomical relations with the structures below. These matter because infection or injury can spread between the sinuses and their neighbours:
- Nasal Cavity - the sinuses drain directly into the nasal cavity.
- Orbit - the maxillary sinus is situated immediately inferior to the orbit. Fractures to the floor of the orbit (‘orbital blow-out’ fracture) can cause the contents of the orbit to prolapse (drop down) into the maxillary sinus.
- Anterior Cranial Fossa (the hollow in the floor of the skull that holds the front of the brain) - the frontal, ethmoidal and sphenoidal sinuses are in close proximity to the anterior cranial fossa.
- Roots of Upper Teeth - these can sometimes project into the maxillary sinuses.
The nasal cavity is supplied by branches of the ophthalmic (eye), maxillary, and facial arteries:
- Anterior ethmoidal artery (ophthalmic a.)
- Posterior ethmoidal artery (ophthalmic a.)
- Sphenopalatine artery (maxillary a.)
- Greater palatine artery (maxillary a.)
- Superior labial artery (facial a.)
These arteries anastomose (join up to form a network) in the anterior nasal septum. This anastomosis is named Kiesselbach’s plexus or Little’s area and is a common source of epistaxis.
Diagram - Arterial supply of the nasal cavity
Creative commons source by Mbuchko3 [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
Venous blood is drained via the sphenopalatine, facial, and ophthalmic veins. There is also a communication with the cavernous sinus (a large venous channel inside the skull, beside the pituitary gland), hence the nose is part of the ‘danger triangle’ of the face, where infections can potentially spread intracranially (into the skull).
Epistaxis (a nosebleed) is often a minor and self-limiting (settles on its own) problem. However, persistent bleeds can be serious and lead to hypovolaemia (low blood volume).
In most cases the cause of the damage to the blood vessels is not identified. Known causes include minor trauma to the nose (for example nose-picking), inflammation of the nasal lining (for example from infection or allergy), medicines that thin the blood (anticoagulants and antiplatelet drugs such as aspirin), coagulopathies (blood clotting disorders), hereditary haemorrhagic telangiectasia (an inherited condition of fragile blood vessels) and tumours.
Epistaxis can be anterior or posterior in origin:
- Anterior - this is the most common source, arising from Kiesselbach’s area.
- Posterior - arising from the sphenopalatine artery. These bleeds are less common and more difficult to treat.
The management steps for epistaxis usually follow the order below, stopping once the bleeding is controlled. Urgent assessment is needed for anyone whose circulation is unstable (for example, a low blood pressure or fast pulse), whose bleeding does not stop after first aid, or who may have a posterior bleed:
- First Aid - sit up with the head tilted forward and the mouth open, then pinch the soft part of the nose (the alar cartilages) firmly, without letting go, for 10 to 15 minutes.
- Cautery (sealing the bleeding vessel, usually with a silver nitrate stick) - used if the bleeding point can be seen.
- Anterior packing (a pack placed in the front of the nose) - used if cautery does not work or the bleeding point cannot be seen, using nasal tampons or an inflatable nasal pack.
- Posterior packing - using a balloon catheter.
- Surgical Intervention (last resort) - either embolisation (blocking the vessel from inside, guided by X-ray imaging) or ligation (tying off the vessel).
Special sensory innervation (the nerve supply for the sense of smell, or olfaction) is via the olfactory nerve (cranial nerve I, or CN I).
The somatosensory innervation (the nerve supply for ordinary sensation, such as touch and pain) of the nasal cavity is via branches of the trigeminal nerve (cranial nerve V, or CN V):
- Anterosuperiorly (front and top) - via the ophthalmic division (CN V1)
- Posteroinferiorly (back and bottom) - via the maxillary division (CN V2)
Conditions Affecting the Nose and Sinuses
Rhinitis is an umbrella term for inflammation of the nasal mucosa. It encompasses both the common cold (coryza) and allergic rhinitis (hay fever). Typical symptoms include nasal irritation, sneezing, nasal discharge and congestion.
The common cold is caused by a range of respiratory viruses, including rhinoviruses, adenoviruses and coronaviruses. It is transmitted via droplet spread and is highly contagious. However, the disease is often mild and self-limiting. In addition to nasal symptoms, individuals may experience fever, fatigue, malaise (a general feeling of being unwell) and sore throat.
Sometimes viral infection can spread from the nose to the paranasal sinuses, resulting in sinusitis (inflammation of the sinuses). About 0.5 to 2% of cases of viral sinusitis develop a bacterial infection (most often with Streptococcus pneumoniae, Haemophilus influenzae or Moraxella catarrhalis). Clinical features include frontal headache, purulent (pus-containing) nasal discharge, facial pain and tenderness, and fever. Sinusitis is normally self-limiting. Bacterial sinusitis is also usually self-limiting, so antibiotics are not routinely needed. NICE advises no antibiotic prescription for symptoms of around 10 days or less. If symptoms last longer without improving, the options are no antibiotic or a back-up prescription (one the patient uses only if symptoms do not improve within 7 days or get rapidly worse). An immediate antibiotic is for people who are very unwell, have signs of a more serious illness or are at high risk of complications. Bacterial sinusitis is more likely if several of these are present: symptoms for more than 10 days, discoloured or purulent nasal discharge, severe pain on one side of the face (especially over the teeth and jaw), fever, and a marked worsening after an initial milder phase. Swelling around the eye, double vision, swelling over the forehead or a severe frontal headache suggest a complication and need referral to hospital.
Hay fever is a manifestation of a Type I hypersensitivity reaction (allergy). B cells (a type of white blood cell) recognise allergens and produce IgE (immunoglobulin E, an antibody), which binds to mast cells (immune cells that store histamine). When the same allergen is met again, the mast cells release histamine and other inflammatory substances, resulting in local inflammation. Common allergens include pollen, dust mites, animal dander (tiny flakes of skin and fur) and mould. Hay fever also commonly affects the eyes and is associated with other atopic (allergy-prone) illness such as asthma and eczema. Avoiding the allergen helps where this is possible. First-line drug treatment is an intranasal corticosteroid (a steroid spray used in the nose), an antihistamine (a non-sedating tablet or a nasal spray), or both together. Intranasal corticosteroids are the most effective treatment and are suggested first for moderate to severe or persistent symptoms.
Nasal polyps are fleshy benign growths of the nasal mucosa. Affected individuals may complain of nasal discharge (with or without blood), blocked nose, loss of smell or taste, cough (due to post-nasal drip, which is mucus running down the back of the throat) and snoring. Nasal polyps are usually bilateral. Persistent unilateral symptoms, such as nasal obstruction, discharge or nosebleeds, should raise suspicion of a sinonasal tumour (a tumour of the nose and sinuses) and need an urgent suspected cancer pathway referral.
In children, another important differential for nasal discharge is a foreign body (an object pushed into the nose), which typically causes a unilateral discharge or blockage.
Reviewed by: Dr. Thomas Burnell and Dr. Marcus Judge
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