Nasal concha

Inanatomy, anasal concha(/ˈkɒnkə/;pl.:conchae;/ˈkɒnkiː/;Latinfor 'shell'), also called anasal turbinateorturbinal,is a long, narrow, curled shelf ofbonethat protrudes into the breathing passage of thenosein humans and various other animals. The conchae are shaped like an elongatedseashell, which gave them their name (Latinconchafrom Greekκόγχη). A concha is any of the scrolled spongybonesof thenasal passagesinvertebrates.
In humans, the conchae divide the nasal airway into four groove-like air passages, and are responsible for forcing inhaled air to flow in a steady, regular pattern around the largest possiblesurface areaofnasal mucosa. As aciliatedmucous membrane with shallow blood supply, the nasal mucosa cleans, humidifies and warms the inhaled air in preparation for thelungs.
A rapidly dilating arteriolar circulation to these bones may lead to a sharp increase in the pressure within, in response to acute cooling of the body core. The pain from this pressure is often referred to as "brain freeze", and is frequently associated with the rapid consumption ofice cream. The shallowness of the venous blood supply of the mucosa contributes to the ease with whichnosebleedcan occur.
Conchae are composed ofpseudostratifiedcolumnar,ciliatedrespiratory epitheliumwith a thick,vascular, and erectileglandulartissue layer.The conchae are located laterally in the nasal cavities, curlingmediallyand downward into the nasal airway. Each pair is composed of one concha in either side of the nasal cavity, divided by theseptum.
Thesuperior conchaeare smaller structures, connected to the middle conchae by nerve-endings, and serve to protect theolfactory bulb.  Thesuperior conchaeattach to theethmoid bone. The openings to the posterior ethmoidal sinuses exist under the superior meatus.Thesphenoid sinusostium exists medial to the superior turbinate.
Themiddle conchaeare smaller but have the most complex anatomy of the nasal turbinates. They originate from the lateral edge of thecribriform plateof theethmoid bone. They insert anteriorly into thefrontal processof themaxillaand posteriorly into theperpendicular plateof thepalatine bone.There are three mutually perpendicular segments of the middle turbinate: from proximal to distal, there is the horizontal segment (axial plane), thebasal lamella(coronal plane), and the vertical segment (sagittal plane). They project downwards over the openings of themaxillaryandanterior and middle ethmoidsinuses, and act as buffers to protect the sinuses from coming in direct contact with pressurized nasal airflow. Most inhaled airflow travels between the inferior concha and themiddle meatus.In humans, they are usually as long as thelittle finger.
Theinferior conchaeare the largest turbinates, can be as long as theindex fingerin humans, and are responsible for the majority of airflow direction, humidification, heating, and filtering of air inhaled through the nose.
Theinferior conchaeare graded 1–4 based on the inferior concha classification system (known as theinferior turbinate classification system) in which the total amount of the airway space that the inferior concha takes up is estimated. Grade 1 is 0–25% of the airway, grade 2 is 26–50% of the airway, grade 3 is 51–75% of the airway and grade 4 is 76–100% of the airway.
There is sometimes a pair ofsupreme conchaesuperior to the superior conchae. When present, these usually take the form of a small crest.
The conchae comprise most of themucosaltissue of thenoseand are required for functionalrespiration. They are enriched with airflow pressure and temperature-sensing nerve receptors (linked to thetrigeminal nerveroute, thefifth cranial nerve), allowing for tremendous erectile capabilities ofnasal congestionand decongestion, in response to theweatherconditions and changing needs of the body.In addition, the erectile tissue undergoes an often unnoticed cycle of partial congestion and decongestion called thenasal cycle. The flow of blood to the nasal mucosa in particular thevenous plexus of the conchaeis regulated by thepterygopalatine ganglionand heats or cools the air in the nose.
The nasopulmonary and nasothoracicreflexesregulate the mechanism of breathing through deepening of inhalation. Triggered by the flow of the air, the pressure of the air in the nose, and the quality of the air, impulses from the nasal mucosa are transmitted by the trigeminal nerve to thebreathing centresin thebrainstem, and the generated response is transmitted to thebronchi, theintercostal muscles, and thediaphragm.
The conchae are also responsible forfiltration, heating, and humidification of air inhaled through the nose. Of these three, filtration is achieved mostly by other more effective means such as mucus and cilia. As air passes over the conchae, it is heated to 32–34 °C (89–93 °F), humidified (up to 98%water saturation) and filtered.
Therespiratory epitheliumthat covers the erectile tissue (orlamina propria) of the conchae plays a major role in the body's first line ofimmunologicaldefense. Therespiratory epitheliumis partially composed ofmucus-producinggoblet cells. This secreted mucus covers the nasal cavities, and serves as a filter, by trapping air-borne particles larger than 2 to 3micrometers. The respiratory epithelium also serves as a means of access for thelymphatic system, which protects the body from being infected by viruses or bacteria.
The conchae provide, first and foremost, the humidity needed to preserve the delicateolfactory epithelium, which in turn is needed to keep the olfactory receptors healthy and alert. If the epithelial layer gets dry or irritated, it may cease to function. This is usually a temporary condition but, over time, may lead to chronicanosmia.The turbinates also increase thesurface areaof the inside of the nose, and, by directing and deflecting airflow across the maximum mucosal surface of the inner nose, they are able to propel the inspired air. This, coupled with the humidity and filtration provided by the conchae, helps to carry more scent molecules towards the higher, and very narrow regions of the nasal airways, where olfaction nerve receptors are located.
The superior conchae completely cover and protect the nerve axons piercing through thecribriform plate(a porous bone plate that separates the nose from the brain) into the nose. Some areas of the middle conchae are alsoinnervatedby the olfactory bulb. All three pairs of conchae are innervated bypainandtemperaturereceptors, via thetrigeminal nerve(or, the fifthcranial nerve).Research has shown that there is a strong connection between these nerve endings and activation of the olfactory receptors, but science has yet to fully explain this interaction.
Large, swollen conchae, often referred to clinically as turbinates, may lead to blockage of nasal breathing.Allergies, exposure to environmentalirritants, or a persistentinflammationwithin the sinuses can lead to turbinate swelling. Deformity of thenasal septumcan also result in enlarged turbinates.
Treatment of the underlying allergy or irritant may reduce turbinate swelling. In cases that do not resolve, or for treatment ofdeviated septum, turbinate surgery may be required.
Turbinate reductionis a surgery to reduce the size of the turbinates (typicallyinferior turbinates). There are different techniques, including bipolarradiofrequency ablation(also known assomnoplasty),electrocautery, and use of cold steel instruments (e.g. microdebrider).
In the case of turbinate reduction, only small amounts of turbinate tissue are removed because the turbinates are essential for respiration. Turbinectomy is usually reserved for patients who have persistent symptoms despite previous turbinate reduction surgery. Risks of reduction of the inferior or middle turbinates includeempty nose syndrome.As Steven M. Houser suggested, "this is especially true in cases of anterior inferior turbinate (IT) resection because of its important role in the internal nasal valve."
Concha bullosais an abnormal pneumatization of the middle turbinate, which may interfere with normal ventilation of thesinus ostiaand can result in recurrentsinusitis. In some cases, the concha bullosa may be resected to help resolve persistent symptoms.
Generally, in animals, nasal conchae are convoluted structures of thin bone or cartilage located in thenasal cavity. These are lined withmucous membranesthat can perform two functions. They can improve the sense of smell by increasing the area available to absorb airborne chemicals, and they can warm and moisten inhaled air, and extract heat and moisture from exhaled air to preventdesiccationof the lungs.Olfactoryturbinates are found in all livingtetrapods,andrespiratoryturbinates are found in most mammals and birds.
Animals with respiratory turbinates can breathe faster without drying out their lungs, and consequently can have a faster metabolism.For example, when theemuexhales, its nasal turbinates condense moisture from the air and absorbs it for reuse.Dogsand othercanidspossess well-developed nasal turbinates.These turbinates allow for heat exchange between small arteries and veins on theirmaxilloturbinate(turbinates positioned onmaxillabone) surfaces in a counter-current heat-exchange system.Dogs are capable of prolonged chases, in contrast to the ambush predation of cats, and these complex turbinates play an important role in enabling this (cats only possess a much smaller and less-developed set of nasal turbinates).This same complex turbinate structure help conserve water in arid environments.The water conservation and thermoregulatory capabilities of these well-developed turbinates in dogs may have been crucial adaptations that allowed dogs (including both domestic dogs and their wild prehistoricgray wolfancestors) to survive in the harshArcticenvironment and other cold areas of northern Eurasia and North America, which are both very dry and very cold.
Reptilesand more primitivesynapsidshave olfactory turbinates that are involved in sensing smell rather than preventing desiccation.While the maxilloturbinates of mammals are located in the path of airflow to collect moisture, sensory turbinates in both mammals and reptiles are positioned farther back and above the nasal passage, away from the flow of air.Glanosuchushas ridges positioned low in the nasal cavity, indicating that it had maxilloturbinates that were in the direct path of airflow. The maxilloturbinates may not have been preserved because they were either very thin orcartilaginous. The possibility has also been raised that these ridges are associated with an olfactoryepitheliumrather than turbinates.Nonetheless, the possible presence of maxilloturbinates suggests thatGlanosuchusmay have been able to rapidly breathe without drying out the nasal passage, and therefore could have been an endotherm.
The bones of nasal turbinates are very fragile and seldom survive as fossils. In particular none have been found in fossil birds.But there is indirect evidence for their presence in some fossils. Rudimentary ridges like those that support respiratory turbinates have been found in advanced Triassiccynodonts, such asThrinaxodonandDiademodon. This suggests that they may have had fairly high metabolic rates.The paleontologistJohn Rubenand others have argued that no evidence of nasal turbinates has been found in dinosaurs. All the dinosaurs they examined had nasal passages that they claimed were too narrow and too short to accommodate nasal turbinates, so dinosaurs could not have sustained the breathing rate required for a mammal-like or bird-like metabolic rate while at rest, because their lungs would have dried out.However, objections have been raised against this argument. Nasal turbinates are absent or very small in some birds, such asratites,ProcellariiformesandFalconiformes. They are also absent or very small in some mammals, such as anteaters, bats, elephants, whales and most primates, although these animals are fully endothermic and in some cases very active.Furthermore, ossified turbinate bones have been identified in theankylosauriddinosaurSaichania.