Nose
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A nose is a protuberance in
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...
s that houses the
nostril A nostril (or naris , plural ''nares'' ) is one of the two channels of the nose, from the point where they bifurcate to the external opening. In bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class ...
s, or nares, which receive and expel air for
respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellular ...
alongside the
mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...

mouth
. Behind the nose are the
olfactory mucosa The olfactory mucosa is located in the upper region of the nasal cavity The nasal cavity is a large, air-filled space above and behind the nose A nose is a protuberance in vertebrate Vertebrates () comprise all species of animal A ...
and the
sinuses Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity The nasal cavity is a large, air-filled space above and behind the nose A nose is a protuberance in vertebrate Vertebrates () comprise all speci ...
. Behind the
nasal cavity The nasal cavity is a large, air-filled space above and behind the human nose, nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. ...

nasal cavity
, air next passes through the
pharynx The pharynx (plural: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, thou ...

pharynx
, shared with the digestive system, and then into the rest of the
respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system A biological system is a complex network which connects several biologically relevant entities. Biological organization spans several scales and are d ...

respiratory system
. In humans, the nose is located centrally on the face and serves as an alternative respiratory passage especially during suckling for
infant 222x222px, Eight-month-old sororal twin sisters An infant (from the Latin word ''infans'', meaning 'unable to speak' or 'speechless') is the more formal or specialised synonym for the common term ''baby'', meaning the very young offspring ...

infant
s. The protruding nose that completely separate from the mouth part is a characteristic found only in therian mammals. It has been theorized that this unique mammalian nose evolved from the anterior part of the upper jaw of the reptilian-like ancestors (
synapsids Synapsids are a group of animals that includes mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glan ...
).


Air treatment

Acting as the first interface between the external environment and an animal's delicate internal lungs, a nose conditions incoming air, both as a function of thermal regulation and filtration during respiration, as well as enabling the sensory perception of smell. Hair inside nostrils filter incoming air, as a first line of defense against dust particles, smoke, and other potential obstructions that would otherwise inhibit respiration, and as a kind of filter against airborne illness. In addition to acting as a filter, mucus produced within the nose supplements the body's effort to maintain temperature, as well as contributes moisture to integral components of the respiratory system. Capillary structures of the nose warm and humidify air entering the body; later, this role in retaining moisture enables conditions for alveoli to properly exchange O2 for CO2 (i.e., respiration) within the lungs. During exhalation, the capillaries then aid recovery of some moisture, mostly as a function of thermal regulation, again.


Sense of direction

The wet nose of dogs is useful for the perception of direction. The sensitive cold receptors in the skin detect the place where the nose is cooled the most and this is the direction a particular smell that the animal just picked up comes from.


Structure in air-breathing forms

In
amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial animal, ter ...
s and
lungfish Lungfish are freshwater rhipidistian vertebrates belonging to the Order (taxonomic rank), order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral ...
, the nostrils open into small sacs that, in turn, open into the forward roof of the mouth through the
choana The choanae (singular choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the throat in tetrapods, including humans and other mammals (as well as crocodilian ...
e. These sacs contain a small amount of olfactory epithelium, which, in the case of
caecilian Caecilians (; New Latin New Latin (also called Neo-Latin or Modern Latin) is the revival of Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was origina ...

caecilian
s, also lines a number of neighbouring tentacles. Despite the general similarity in structure to those of amphibians, the nostrils of lungfish are not used in respiration, since these animals breathe through their mouths. Amphibians also have a
vomeronasal organ The vomeronasal organ (VNO), or Jacobson's organ, is the paired auxiliary olfactory (smell) sense organ located in the soft tissue of the nasal septum, in the nasal cavity just above the roof of the mouth (the hard palate). The name is derived from ...

vomeronasal organ
, lined by olfactory epithelium, but, unlike those of
amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade A clade (; from grc, , ''klados'', "bran ...
s, this is generally a simple sac that, except in
salamander Salamanders are a group of amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most spe ...

salamander
s, has little connection with the rest of the nasal system. In
reptile Reptiles, as most commonly defined, are the animals in the Class (biology), class Reptilia , a paraphyletic grouping comprising all amniotes except synapsids (mammals and their extinct relatives) and Aves (birds). Living reptiles comprise turtl ...

reptile
s, the nasal chamber is generally larger, with the choanae located much further back in the roof of the mouth. In
crocodilian Crocodilia (or Crocodylia, both ) is an Order (biology), order of mostly large, predatory, List of semiaquatic tetrapods, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous Period (g ...
s, the chamber is exceptionally long, helping the animal to breathe while partially submerged. The reptilian nasal chamber is divided into three parts: an anterior ''vestibule'', the main olfactory chamber, and a posterior
nasopharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the esophagus The esophagus (American English) or oesophagus (British English; American and British English spelling differences#ae and ...
. The olfactory chamber is lined by olfactory epithelium on its upper surface and possesses a number of
turbinate In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any in ...
s to increase the sensory area. The vomeronasal organ is well-developed in lizards and snakes, in which it no longer connects with the nasal cavity, opening directly into the roof of the mouth. It is smaller in turtles, in which it retains its original nasal connection, and is absent in adult crocodilians. Birds have a similar nose to reptiles, with the nostrils located at the upper rear part of the beak. Since they generally have a poor sense of smell, the olfactory chamber is small, although it does contain three turbinates, which sometimes have a complex structure similar to that of mammals. In many birds, including doves and fowls, the nostrils are covered by a horny protective shield. The vomeronasal organ of birds is either under-developed or altogether absent, depending on the species. The nasal cavities in mammals are both fused into one. Among most species they are exceptionally large, typically occupying up to half the length of the skull. In some groups, however, including primates, bats, and cetaceans, the nose has been secondarily reduced, and these animals consequently have a relatively poor sense of smell. The nasal cavity of mammals has been enlarged, in part, by the development of a palate cutting off the entire upper surface of the original oral cavity, which consequently becomes part of the nose, leaving the palate as the new roof of the mouth. The enlarged nasal cavity contains complex turbinates forming coiled scroll-like shapes that help to warm the air before it reaches the lungs. The cavity also extends into neighbouring skull bones, forming additional air cavities known as paranasal sinuses. In cetaceans, the nose has been reduced to one or two blowhole (anatomy), blowholes, which are the nostrils that have migrated to the top of the head. This adaptation gave cetaceans a more streamlined body shape and the ability to breathe while mostly submerged. Conversely, the elephant's nose has elaborated into a long, muscular, manipulative organ called the Elephant#Trunk, trunk. The vomeronasal organ of mammals is generally similar to that of reptiles. In most species, it is located in the floor of the nasal cavity, and opens into the mouth via two ''nasopalatine ducts'' running through the palate, but it opens directly into the nose in many rodents. It is, however, lost in bats, and in many primates, including humans.


In fish

Fish have a relatively good sense of smell. Unlike that of tetrapods, the nose has no connection with the mouth, nor any role in respiration. Instead, it generally consists of a pair of small pouches located behind the nostrils at the front or sides of the head. In many cases, each of the nostrils is divided into two by a fold of skin, allowing water to flow into the nose through one side and out through the other. The pouches are lined by olfactory epithelium, and commonly include a series of internal folds to increase the surface area, often forming an elaborate "olfactory rosette". In some teleosts, the pouches branch off into additional sinus-like cavities, while in coelacanths, they form a series of tubes. In the earliest vertebrates, there was only one nostril and olfactory pouch, and the nasal passage was connected to the pituitary gland, hypophysis. The same anatomy is observed in the most primitive living vertebrates, the lampreys and hagfish. In gnathostome ancestors, the olfactory apparatus gradually became paired (presumably to allow sense of direction of smells), and freeing the midline from the nasal passage allowed evolution of jaws.


See also

* Human nose * Nasal bridge * Obligate nasal breathing * Rhinarium, the wet, naked surface around the nostrils in most mammals, absent in Haplorrhini, haplorrhine primates such as humans


References


External links

* * {{Authority control Nose, Human head and neck Respiratory system Olfactory system Facial features