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The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air- breathing
animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...
s with lungs. The trachea extends from the larynx and branches into the two primary bronchi. At the top of the trachea the cricoid cartilage attaches it to the larynx. The trachea is formed by a number of horseshoe-shaped rings, joined together vertically by overlying
ligaments A ligament is the fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body include the: * Peritoneal ...
, and by the
trachealis muscle The trachealis muscle is a sheet of smooth muscle in the trachea. Structure The trachealis muscle lies posterior to the trachea and anterior to the oesophagus. It bridges the gap between the free ends of C-shaped rings of cartilage at the poste ...
at their ends. The
epiglottis The epiglottis is a leaf-shaped flap in the throat that prevents food and water from entering the trachea and the lungs. It stays open during breathing, allowing air into the larynx. During swallowing, it closes to prevent aspiration of food in ...
closes the opening to the larynx during swallowing. The trachea begins to form in the second month of embryo development, becoming longer and more fixed in its position over time. It is epithelium lined with column-shaped cells that have hair-like extensions called cilia, with scattered goblet cells that produce protective mucins. The trachea can be affected by inflammation or infection, usually as a result of a viral illness affecting other parts of the respiratory tract, such as the larynx and bronchi, called croup, that can result in a barking cough. Infection with bacteria usually affects the trachea only and can cause narrowing or even obstruction. As a major part of the respiratory tract, when obstructed the trachea prevents air entering the lungs and so a tracheostomy may be required if the trachea is obstructed. Additionally, during surgery if mechanical ventilation is required when a person is sedated, a tube is inserted into the trachea, called intubation. The word ''trachea'' is used to define a very different organ in invertebrates than in vertebrates. Insects have an open respiratory system made up of spiracles, tracheae, and tracheoles to transport metabolic gases to and from tissues.


Structure

An adult's trachea has an inner diameter of about and a length of about ; wider in males than females. The trachea begins at the lower edge of the cricoid cartilage of the larynx at the level of sixth cervical vertebra (C6) and ends at the carina, the point where the trachea branches into left and right main bronchi., at the level of the fourth thoracic vertebra (T4), although its position may change with breathing. The trachea is surrounded by 16–20 rings of hyaline cartilage; these 'rings' are 4 millimetres high in the adult, incomplete and C-shaped. Ligaments connect the rings. The
trachealis muscle The trachealis muscle is a sheet of smooth muscle in the trachea. Structure The trachealis muscle lies posterior to the trachea and anterior to the oesophagus. It bridges the gap between the free ends of C-shaped rings of cartilage at the poste ...
connects the ends of the incomplete rings and runs along the back wall of the trachea. Also adventitia, which is the outermost layer of connective tissue that surrounds the hyaline cartilage, contributes to the trachea's ability to bend and stretch with movement. Although trachea is a midline structure, it can be displaced normally to the right by the aortic arch.


Nearby structures

The trachea passes by many structures of the neck and chest ( thorax) along its course. In front of the upper trachea lies connective tissue and skin. Several other structures pass over or sit on the trachea; the jugular arch, which joins the two anterior jugular veins, sits in front of the upper part of the trachea. The sternohyoid and sternothyroid muscles stretch along its length. The thyroid gland also stretches across the upper trachea, with the isthmus overlying the second to fourth rings, and the lobes stretching to the level of the fifth or sixth cartilage. The blood vessels of the thyroid rest on the trachea next to the isthmus; superior thyroid arteries join just above it, and the inferior thyroid veins below it. In front of the lower trachea lies the manubrium of the sternum, the
remnants Remnant or remnants may refer to: Religion * Remnant (Bible), a recurring theme in the Bible * Remnant (Seventh-day Adventist belief), the remnant theme in the Seventh-day Adventist Church * ''The Remnant'' (newspaper), a traditional Catholic n ...
of the
thymus The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or '' T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders ...
in adults. To the front left lie the large blood vessels the aortic arch and its branches the left common carotid artery and the brachiocephalic trunk; and the left
brachiocephalic vein The left and right brachiocephalic veins (previously called innominate veins) are major veins in the upper chest, formed by the union of each corresponding internal jugular vein and subclavian vein. This is at the level of the sternoclavicular ...
. The deep cardiac plexus and lymph nodes are also positioned in front of the lower trachea. Behind the trachea, along its length, sits the
oesophagus The esophagus ( American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to ...
, followed by connective tissue and the vertebral column. To its sides run the carotid arteries and inferior thyroid arteries; and to its sides on its back surface run the recurrent laryngeal nerves in the upper trachea, and the
vagus nerves The vagus nerve, also known as the tenth cranial nerve, cranial nerve X, or simply CN X, is a cranial nerve that interfaces with the parasympathetic control of the heart, lungs, and digestive tract. It comprises two nerves—the left and right v ...
in the lower trachea. The trachealis muscle contracts during coughing, reducing the size of the lumen of the trachea. File:CT-Thorax-5.0-B70f.ogg, CT scan of the thorax (axial lung window) File:COR-2-STND-CHEST.ogg, CT scan of the thorax (coronal lung window) File:COR-2-STND-CHEST-MEDIASTINUM.ogg, CT scan of the thorax (coronal mediastinal window) File:Cross section of a trachea and esophagus.svg, Cross section of a trachea and esophagus File:Sternohyoid muscle.PNG, The sternohyoid and sternothyroid muscles lie on top of the upper part of the trachea File:Blausen 0534 Goiter.png, The thyroid gland also lies on top of the trachea, and lies below the cricoid cartilage.


Blood and lymphatic supply

The upper part of trachea receives and drains
blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...
through the
inferior thyroid arteries The inferior thyroid artery is an artery in the neck. It arises from the thyrocervical trunk and passes upward, in front of the vertebral artery and longus colli muscle. It then turns medially behind the carotid sheath and its contents, and als ...
and veins; the lower trachea receives blood from bronchial arteries. Arteries that supply the trachea do so via small branches that supply the trachea from the sides. As the branches approach the wall of the trachea, they split into inferior and superior branches, which join with the branches of the arteries above and below; these then split into branches that supply the anterior and posterior parts of the trachea. The inferior thyroid arteries arise just below the isthmus of the thyroid, which sits atop the trachea. These arteries join () with ascending branches of the
bronchial arteries In human anatomy, the bronchial arteries supply the lungs with nutrition and oxygenated blood. Although there is much variation, there are usually two bronchial arteries that run to the left lung, and one to the right lung and are a vital part ...
, which are direct branches from the aorta, to supply blood to the trachea. The lymphatic vessels of the trachea drain into the pretracheal nodes that lie in front of the trachea, and paratracheal lymph nodes that lie beside it.


Development

In the fourth week of development of the human embryo as the respiratory bud grows, the trachea separates from the foregut through the formation of ridges which eventually separate the trachea from the oesophagus, the
tracheoesophageal septum The tracheoesophageal septum is an embryological structure. It is formed from the tracheoesophageal folds or ridges which fuse in the midline. It divides the oesophagus from the trachea during prenatal development. Developmental abnormalities can ...
. This separates the future trachea from the oesophagus and divides the foregut tube into the laryngotracheal tube. By the start of the fifth week, the left and right main bronchi have begin to form, initially as buds at the terminal end of the trachea. The trachea is no more than 4mm diameter during the first year of life, expanding to its adult diameter of approximately 2cm by late childhood. The trachea is more circular and more vertical in children compared to adults, varies more in size, and also varies more in its position in relation to its surrounding structures.


Microanatomy

The trachea is lined with a layer of interspersed layers of column-shaped cells with cilia. The epithelium contains goblet cells, which are glandular, column-shaped cells that produce
mucins Mucins () are a family of high molecular weight, heavily glycosylated proteins (glycoconjugates) produced by epithelial tissues in most animals. Mucins' key characteristic is their ability to form gels; therefore they are a key component in most ...
, the main component of
mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It ...
. Mucus helps to moisten and protect the airways. Mucus lines the
ciliated The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike proj ...
cells of the trachea to trap inhaled foreign particles that the cilia then waft upward toward the larynx and then the pharynx where it can be either swallowed into the stomach or expelled as
phlegm Phlegm (; , ''phlégma'', "inflammation", " humour caused by heat") is mucus produced by the respiratory system, excluding that produced by the nasal passages. It often refers to respiratory mucus expelled by coughing, otherwise known as sput ...
. This self-clearing mechanism is termed mucociliary clearance. The trachea is surrounded by 16 to 20 rings of hyaline cartilage; these 'rings' are incomplete and C-shaped. Two or more of the cartilages often unite, partially or completely, and they are sometimes bifurcated at their extremities. The rings are generally highly elastic but they may
calcify Hard tissue, refers to "normal" calcified tissue, is the tissue which is mineralized and has a firm intercellular matrix. The hard tissues of humans are bone, tooth enamel, dentin, and cementum. The term is in contrast to soft tissue. Bone Bone ...
with age. File:Gray964.png, Cross-section File:2308 The Trachea-b.jpg, Cross-section of the trachea, with pseudostratified ciliated columnar epithelium and goblet cells labelled File:Cartilage01.JPG, Magnified cross-section of the cartilage of the trachea.


Function

The trachea is one part of the
respiratory tree The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa. Air is breathed in through the nose to th ...
that is a conduit for air to pass through on its way to or from the alveoli of the lungs. This transmits
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
to the body and removes
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
.


Clinical significance


Inflammation and infection

Inflammation of the trachea is known as tracheitis, usually due to an infection. It is usually caused by viral infections, with bacterial infections occurring almost entirely in children. Most commonly, infections occur with inflammation of other parts of the respiratory tract, such as the larynx and bronchi, known as croup, however bacterial infections may also affect the trachea alone, although they are often associated with a recent viral infection. Viruses that cause croup are generally the parainfluenza viruses 1–3, with influenza viruses A and B also causing croup, but usually causing more serious infections; bacteria may also cause croup and include '' Staphylococcus aureus'', '' Haemophilus influenzae'', '' Streptococcus pneumoniae'' and '' Moraxella catarrhalis''. Causes of bacterial infection of the trachea are most commonly '' Staphylococcus aureus'' and '' Streptococcus pneumoniae''. In patients who are in hospital, additional bacteria that may cause tracheitis include '' Escherichia coli'', '' Klebsiella pneumoniae'', and '' Pseudomonas aeruginosa''. A person affected with tracheitis may start with symptoms that suggest an upper respiratory tract infection such as a cough, sore throat, or coryzal symptoms such as a
runny nose Rhinorrhea, rhinorrhoea, or informally runny nose is the free discharge of a thin mucus fluid from the nose; it is a common condition. It is a common symptom of allergies ( hay fever) or certain viral infections, such as the common cold or COV ...
. Fevers may develop and an affected child may develop
difficulty breathing Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing disc ...
and sepsis. Swelling of the airway can cause narrowing of the airway, causing a hoarse breathing sound called stridor, or even cause complete blockage. Unfortunately, up to 80% of people affected by bacterial tracheitis require the use of mechanical ventilation, and treatment may include endoscopy for the purposes of acquiring microbiological specimens for culture and sensitivity, as well as removal of any dead tissue associated with the infection. Treatment in such situations usually includes
antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and preventio ...
.


Narrowing

A trachea may be narrowed or compressed, usually a result of enlarged nearby lymph nodes; cancers of the trachea or nearby structures; large thyroid goitres; or rarely as a result of other processes such as unusually swollen blood vessels. Scarring from
tracheobronchial injury Tracheobronchial injury is damage to the tracheobronchial tree (the airway structure involving the trachea and bronchi). It can result from blunt or penetrating trauma to the neck or chest, inhalation of harmful fumes or smoke, or aspiration of ...
or intubation; or inflammation associated with granulomatosis with polyangiitis may also cause a narrowing of the trachea ( tracheal stenosis). Obstruction invariably causes a harsh breathing sound known as stridor. A camera inserted via the mouth down into the trachea, called bronchoscopy, may be performed to investigate the cause of an obstruction. Management of obstructions depends on the cause. Obstructions as a result of malignancy may be managed with surgery,
chemotherapy Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemother ...
or radiotherapy. A stent may be inserted over the obstruction. Benign lesions, such as narrowing resulting from scarring, are likely to be surgically excised. One cause of narrowing is tracheomalacia, which is the tendency for the trachea to collapse when there is increased external pressure, such as when airflow is increased during breathing in or out, due to decreased
compliance Compliance can mean: Healthcare * Compliance (medicine), a patient's (or doctor's) adherence to a recommended course of treatment * Compliance (physiology), the tendency of a hollow organ to resist recoil toward its original dimensions (this is a ...
. It can be due to congenital causes, or due to things that develop after birth, such as compression from nearby masses or swelling, or trauma. Congenital tracheomalacia can occur by itself or in association with other abnormalities such as
bronchomalacia Bronchomalacia is a term for weak cartilage in the walls of the bronchial tubes, often occurring in children under a day. Bronchomalacia means 'floppiness' of some part of the bronchi. Patients present with noisy breathing and/or wheezing. There is ...
or laryngomalacia, and abnormal connections between the trachea and the oesophagus, amongst others. Congenital tracheomalacia often improves without specific intervention; when required, interventions may include
beta agonist Beta adrenergic agonists or beta agonists are medications that relax muscles of the airways, causing widening of the airways and resulting in easier breathing. They are a class of sympathomimetic agents, each acting upon the beta adrenoceptors. ...
s and muscarinic agonists, which enhance the tone of the smooth muscle surrounding the trachea; positive pressure ventilation, or surgery, which may include the placement of a stent, or the removal of the affected part of the trachea. In dogs, particularly miniature dogs and toy dogs, tracheomalacia, as well as
bronchomalacia Bronchomalacia is a term for weak cartilage in the walls of the bronchial tubes, often occurring in children under a day. Bronchomalacia means 'floppiness' of some part of the bronchi. Patients present with noisy breathing and/or wheezing. There is ...
, can lead to tracheal collapse, which often presents with a honking goose-like cough.


Injury

The trachea may be injured by trauma such as in a vehicle accident, or intentionally by another wilfully inflicting damage for example as practiced in some martial arts.


Intubation

Tracheal intubation refers to the insertion of a tube down the trachea. This procedure is commonly performed during
surgery Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pa ...
, in order to ensure a person receives enough oxygen when sedated. The catheter is connected to a machine that monitors the airflow, oxygenation and several other metrics. This is often one of the responsibilities of an anaesthetist during surgery. In an emergency, or when tracheal intubation is deemed impossible, a tracheotomy is often performed to insert a tube for ventilation, usually when needed for particular types of surgery to be carried out so that the airway can be kept open. The provision of the opening via a tracheotomy is called a tracheostomy. Another method procedure can be carried, in an emergency situation, and this is a
cricothyrotomy A cricothyrotomy (also called cricothyroidotomy) is an incision made through the skin and cricothyroid membrane to establish a patent airway during certain life-threatening situations, such as airway obstruction by a foreign body, angioedema, or ...
.


Congenital disorders

Tracheal agenesis Tracheal agenesis (also known as tracheal atresia) is a rare birth defect with a prevalence of less than 1 in 50,000 in which the trachea fails to develop, resulting in an impaired communication between the larynx and the alveoli of the lungs. A ...
is a rare birth defect in which the trachea fails to develop. The defect is usually fatal though sometimes surgical intervention has been successful. A
tracheoesophageal fistula A tracheoesophageal fistula (TEF, or TOF; see spelling differences) is an abnormal connection ( fistula) between the esophagus and the trachea. TEF is a common congenital abnormality, but when occurring late in life is usually the sequela of surg ...
is a congenital defect in which the trachea and esophagus are abnormally connected (a ). This is because of abnormalities in the separation between the trachea and oesophagus during development. This occurs in approximately 1 in 3000 births, and the most common abnormalities is a separation of the upper and lower ends of the oesophagus, with the upper end finishing in a closed pouch. Other abnormalities may be associated with this, including cardiac abnormalities, or
VACTERL syndrome The VACTERL association (also VATER association, and less accurately VACTERL syndrome) refers to a recognized group of birth defects which tend to co-occur (see below). This pattern is a recognized association, as opposed to a syndrome, because t ...
. Such fistulas may be detected before a baby is born because of excess amniotic fluid; after birth, they are often associated with pneumonitis and pneumonia because of of food contents. Congenital fistulas are often treated by surgical repair. In adults, fistulas may occur because of erosion into the trachea from nearby malignant tumours, which erode into both the trachea and the oesophagus. Initially, these often result in coughing from swallowed contents of the oesophagus that are aspirated through the trachea, often progressing to fatal pneumonia; unfortunately, there is rarely a curative treatment. A tracheo-oesophageal puncture is a surgically created hole between the trachea and the esophagus in a person who has had their larynx removed. Air travels upwards from the surgical connection to the upper oesophagus and the pharynx, creating vibrations that create sound that can be used for speech. The purpose of the puncture is to restore a person's ability to speak after the vocal cords have been removed. Sometimes as an
anatomical variation An anatomical variation, anatomical variant, or anatomical variability is a presentation of body structure with morphological features different from those that are typically described in the majority of individuals. Anatomical variations are categ ...
one or more of the tracheal rings are formed as complete rings, rather than horseshoe shaped rings. These ''O'' rings are smaller than the normal C-shaped rings and can cause narrowing () of the trachea, resulting in breathing difficulties. An operation called a ''slide tracheoplasty'' can open up the rings and rejoin them as wider rings, shortening the length of the trachea. Slide tracheoplasty is said to be the best option in treating tracheal stenosis.
Mounier-Kuhn syndrome Tracheobronchomegaly is a very rare congenital disorder of the lung primarily characterized by an abnormal widening of the upper airways. The abnormally widened trachea and mainstem bronchi are associated with recurrent lower respiratory tract inf ...
is a rare congenital disorder of an abnormally enlarged trachea, characterised by absent elastic fibres, smooth muscle thinning, and a tendency to get recurrent respiratory tract infections.


Replacement

From 2008, operations have experimentally replaced tracheas, with those grown from stem cells, or with synthetic substitutes, however this is regarded as experimental and there is no standardised method. Difficulties with ensuring adequate blood supply to the replaced trachea is considered a major challenge to any replacement. Additionally, no evidence has been found to support the placement of stem cells taken from bone marrow on the trachea as a way of stimulating tissue regeneration, and such a method remains hypothetical. In January 2021, surgeons at Mount Sinai Hospital in New York performed the first complete trachea transplantation. The 18-hour procedure included harvesting a trachea from a donor and implanting it in the patient, connecting numerous veins and arteries to provide sufficient blood flow to the organ.


Other animals

Allowing for variations in the length of the neck, the trachea in other mammals is, in general, similar to that in humans. Generally, it is also similar to the reptilian trachea.


Vertebrates

In birds, the trachea runs from the pharynx to the syrinx, from which the primary bronchi diverge. Swans have an unusually elongated trachea, part of which is coiled beneath the sternum; this may act as a resonator to amplify sound. In some birds, the tracheal rings are complete, and may even be ossified. In amphibians, the trachea is normally extremely short, and leads directly into the lungs, without clear primary bronchi. A longer trachea is, however, found in some long-necked salamanders, and in caecilians. While there are irregular cartilagenous nodules on the amphibian trachea, these do not form the rings found in amniotes. The only vertebrates to have lungs, but no trachea, are the lungfish and the '' Polypterus'', in which the lungs arise directly from the pharynx.


Invertebrates

The word ''trachea'' is used to define a very different organ in invertebrates than in vertebrates. Insects have an open respiratory system made up of spiracles, tracheae, and tracheoles to transport metabolic gases to and from tissues. The distribution of spiracles can vary greatly among the many
orders Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
of insects, but in general each segment of the body can have only one pair of spiracles, each of which connects to an atrium and has a relatively large tracheal tube behind it. The tracheae are invaginations of the cuticular exoskeleton that branch ( anastomose) throughout the body with diameters from only a few micrometres up to 0.8 mm.
Diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical ...
of oxygen and
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
takes place across the walls of the smallest tubes, called tracheoles, which penetrate tissues and even indent individual cells. Gas may be conducted through the respiratory system by means of active ventilation or passive diffusion. Unlike vertebrates, insects do not generally carry oxygen in their haemolymph. This is one of the factors that may limit their size. A tracheal tube may contain ridge-like circumferential rings of
taenidia Taenidia (singular: taenidium) are circumferential thickenings of the cuticle inside a trachea or tracheole in an insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group with ...
in various
geometries This is a list of geometry topics. Types, methodologies, and terminologies of geometry. * Absolute geometry * Affine geometry * Algebraic geometry * Analytic geometry * Archimedes' use of infinitesimals * Birational geometry * Complex geometr ...
such as loops or helices. Taenidia provide strength and flexibility to the trachea. In the head, thorax, or abdomen, tracheae may also be connected to air sacs. Many insects, such as grasshoppers and
bee Bees are winged insects closely related to wasps and ants, known for their roles in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyletic lineage within the superfami ...
s, which actively pump the air sacs in their abdomen, are able to control the flow of air through their body. In some aquatic insects, the tracheae exchange gas through the body wall directly, in the form of a gill, or function essentially as normal, via a plastron. Note that despite being internal, the tracheae of arthropods are lined with cuticular tissue and are shed during moulting ( ecdysis).


Additional images

File:Trachea (mammal) histology cross-section.png, alt=Trachea (mammal) cross-section high resolution, Trachea (mammal) cross-section high resolution File:Trachea (mammal) histology cross-section low mag.png, alt=Trachea (mammal) cross-section low resolution, Trachea (mammal) cross-section low resolution File:Larynx detailed.jpg, Trachea File:Gray954.png, Coronal section of larynx and upper part of trachea


References

{{good article Arthropod anatomy Invertebrate respiratory system Human head and neck Thorax (human anatomy) Respiratory system