Trachea

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(Redirected from
Tracheal ring
)
For the genus of moth, see
Trachy (currency)
.

Trachea
tracheal branches of inferior thyroid artery
Veinbrachiocephalic vein, azygos vein accessory hemiazygos vein
Identifiers
Latintrachea
MeSHD014132
TA98A06.3.01.001
TA23213
FMA7394
Anatomical terminology]

The trachea (pl.: tracheae or tracheas), also known as the windpipe, is a

ligaments, and by the trachealis muscle at their ends. The epiglottis
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

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

metabolic
gases to and from tissues.

Structure

An adult's trachea has an inner diameter of about 1.5 to 2 centimetres (1⁄2 to 3⁄4 in) and a length of about 10 to 11 cm (4 to 4+1⁄4 in), wider in males than females.

thoracic vertebra (T4),[2] although its position may change with breathing.[3] The trachea is surrounded by 16–20 rings of hyaline cartilage; these 'rings' are 4 millimetres high in the adult, incomplete and C-shaped.[2] Ligaments connect the rings.[3] The trachealis muscle connects the ends of the incomplete rings and runs along the back wall of the trachea.[3] 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.[4]

Although trachea is a midline structure, it can be displaced normally to the right by the aortic arch.[5]

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.

superior thyroid arteries join just above it, and the inferior thyroid veins below it.[2] In front of the lower trachea lies the manubrium of the sternum, the remnants of the thymus 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 deep cardiac plexus and lymph nodes are also positioned in front of the lower trachea.[2]

Behind the trachea, along its length, sits 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 in the lower trachea.[2]

The trachealis muscle contracts during coughing, reducing the size of the lumen of the trachea.[3]

  • CT scan of the thorax (axial lung window)
  • CT scan of the thorax (coronal lung window)
  • CT scan of the thorax (coronal mediastinal window)
  • Cross section of a trachea and esophagus
    Cross section of a trachea and esophagus
  • The sternohyoid and sternothyroid muscles lie on top of the upper part of the trachea
    The sternohyoid and sternothyroid muscles lie on top of the upper part of the trachea
  • The thyroid gland also lies on top of the trachea, and lies below the cricoid cartilage.
    The thyroid gland also lies on top of the trachea, and lies below the cricoid cartilage.

Blood and lymphatic supply

Lymph nodes of the trachea

The upper part of trachea receives and drains

inferior thyroid arteries and veins;[2] the lower trachea receives blood from bronchial arteries.[3] 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.[3] The inferior thyroid arteries arise just below the isthmus of the thyroid, which sits atop the trachea. These arteries join (anastamoses) with ascending branches of the bronchial arteries, which are direct branches from the aorta, to supply blood to the trachea.[2] 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.[2]

Development

In the fourth week of

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. This separates the future trachea from the oesophagus and divides the foregut tube into the laryngotracheal tube.[6] 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.[6]

The trachea is no more than 4 mm in diameter during the first year of life, expanding to its adult diameter of approximately 2cm by late childhood.[2][3] The trachea is more circular and more vertical in children compared to adults,[3] varies more in size, and also varies more in its position in relation to its surrounding structures.[2]

Microanatomy

The trachea is lined with a layer of

ciliated 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. This self-clearing mechanism is termed mucociliary clearance.[8]

The trachea is surrounded by 16 to 20 rings of hyaline cartilage; these 'rings' are incomplete and C-shaped.[2] 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 with age.

  • Cross-section
    Cross-section
  • Cross-section of the trachea, with pseudostratified ciliated columnar epithelium and goblet cells labelled
    Cross-section of the trachea, with pseudostratified ciliated columnar epithelium and goblet cells labelled
  • Magnified cross-section of the cartilage of the trachea
    Magnified cross-section of the cartilage of the trachea

Function

The trachea's main function is to transport air to and from the lungs. It also helps to warm, humidify, and filter the air before it reaches the lungs.

The trachea is made up of rings of cartilage, which help to keep it open and prevent it from collapsing. The inside of the trachea is lined with a mucous membrane, which produces mucus to help trap dirt and dust particles. The cilia, which are tiny hairs that line the mucous membrane, help to move the mucus and trapped particles up and out of the trachea.

Clinical significance

Inflammation and infection

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.[9] Causes of bacterial infection of the trachea are most commonly Staphylococcus aureus and Streptococcus pneumoniae.[11] In patients who are in hospital, additional bacteria that may cause tracheitis include Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa.[9]

A person affected with tracheitis may start with symptoms that suggest an

culture and sensitivity, as well as removal of any dead tissue associated with the infection. Treatment in such situations usually includes antibiotics.[10]

Narrowing

An example of stridor, which develops when the trachea is narrowed or obstructed

A trachea may be

radiotherapy.[12] A stent may be inserted over the obstruction. Benign lesions, such as narrowing resulting from scarring, are likely to be surgically excised.[12]

One cause of narrowing is

toy dogs, tracheomalacia, as well as bronchomalacia,[14] can lead to tracheal collapse, which often presents with a honking goose-like cough.[15]

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.[16]

Intubation

Main articles: Tracheal intubation and Airway management

Tracheal intubation refers to the insertion of a

anaesthetist
during surgery.

In an emergency, or when tracheal intubation is deemed impossible, a

tracheostomy.[18] Another method procedure can be carried, in an emergency situation, and this is a cricothyrotomy.[19]

Congenital disorders

Tracheal diverticulum as seen on axial CT imaging

Tracheal agenesis[20] 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

VACTERL syndrome.[6] 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 aspiration of food contents.[6] Congenital fistulas are often treated by surgical repair.[12] 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; there is rarely a curative treatment.[12] 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.[21]

Sometimes as an anatomical variation 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 (stenosis) 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.[22] Slide tracheoplasty is said to be the best option in treating tracheal stenosis.[23]

Mounier-Kuhn syndrome 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.[24]

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.[25] 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.[25]

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.[26]

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.[27]

Vertebrates

In

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.[27]

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.[27]

The only vertebrates to have lungs, but no trachea, are the lungfish and the Polypterus, in which the lungs arise directly from the pharynx.[27]

Invertebrates

Tracheal system of dissected cockroach. The largest tracheae run across the width of the body of the cockroach and are horizontal in this image. Scale bar, 2 mm.
The tracheal system branches into progressively smaller tubes, here supplying the crop of the cockroach. Scale bar, 2 mm.

The word trachea is used to define a very different organ in

ventilation or passive diffusion. Unlike vertebrates, insects do not generally carry oxygen in their hemolymph.[30]
This is one of the factors that may limit their size.

A tracheal tube may contain ridge-like circumferential rings of taenidia in various geometries 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 bees, 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).[29]

Additional images

  • Trachea (mammal) cross-section high resolution
    Trachea (mammal) cross-section high resolution
  • Trachea (mammal) cross-section low resolution
    Trachea (mammal) cross-section low resolution
  • Trachea
    Trachea
  • Coronal section of larynx and upper part of trachea
    Coronal section of larynx and upper part of trachea

References

  1. ^ "Trachea | Definition of Trachea by Lexico". Lexico Dictionaries | English. Archived from the original on 7 July 2020. Retrieved 27 October 2019.
  2. ^
    OCLC 920806541.{{cite book}}: CS1 maint: location missing publisher (link
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    S2CID 86826724
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    S2CID 42828725
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  11. ^ Bhatia R. "Bacterial Tracheitis - Pediatrics". Merck Manuals Professional Edition. Retrieved 21 May 2020.
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    PMID 25962857
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  16. PMID 29763191
    . Retrieved 23 October 2022.
  17. ^ "Definition of INTUBATION". www.merriam-webster.com. Merriam Webster. Retrieved 25 May 2020.
  18. ^ Molnar H (11 April 2023). "Types of Tracheostomy Tubes".
  19. ^ "Medical Definition of CRICOTHYROTOMY". www.merriam-webster.com. Merriam Webster. Retrieved 25 May 2020.
  20. S2CID 21260092
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  21. ^ "Evaluation and Treatment for Tracheoesophageal Puncture and Prosthesis: Technical Report". American Speech-Language-Hearing Association. American Speech-Language-Hearing Association (ASHA). 2004. Retrieved 26 May 2020.
  22. ^ "Slide tracheoplasty". Retrieved 2 October 2015.
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  25. ^
    PMID 26981270
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  26. ^ Harris R (6 April 2021). "Woman Gets New Windpipe In Groundbreaking Transplant Surgery". NPR. Retrieved 6 April 2021.
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    ISBN 978-0-03-910284-5
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  28. ISBN 0-471-15955-7
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  30. S2CID 43634044
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