The trachea, colloquially called the windpipe, is a cartilaginous tube that connects the pharynx and larynx to the lungs, allowing the passage of air, and so is present in almost all air-breathing animals 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. This is the only complete tracheal ring, the others being incomplete rings of reinforcing cartilage. The trachealis muscle joins the ends of the rings and these are joined vertically by bands of fibrous connective tissue – the annular ligaments of trachea. The epiglottis closes the opening to the larynx during swallowing. The trachea develops in the second month of development. It is lined with an epithelium that has goblet cells which produce protective mucins (see Respiratory epithelium). An inflammatory condition, also involving the larynx and bronchi, called croup can result in a barking cough. A tracheotomy is often performed for ventilation in surgical operations where needed. Intubation is also carried out for the same reason by the inserting of a tube into the trachea. From 2008, operations have experimentally transplanted a windpipe grown by stem cells, and synthetic windpipes; their success is, however, doubtful.
1.1 Development 1.2 Histology
2 Clinical significance
2.1 Inflammation 2.2 Intubation 2.3 Congenital disorders 2.4 Other
3 Other animals
3.1 Vertebrates 3.2 Invertebrates
4 Bioengineering and prosthesis 5 Additional images 6 External links 7 References
An adult's trachea has an inner diameter of about 1.5 to 2 centimetres (0.6 to 0.8 in) and a length of about 10 to 11 centimetres (4 in.). It begins at the bottom of the larynx, and ends at the carina, the point where the trachea branches into left and right main bronchi. The trachea begins level with the sixth cervical vertebra and the carina is found at the level of the fifth thoracic vertebra (T5), opposite the sternal angle and can be positioned up to two vertebrae lower or higher, depending on breathing. The trachea is surrounded by rings of hyaline cartilage; these rings are incomplete and C-shaped. The cricoid cartilage is attached to the first tracheal ring at top of the trachea and acts as the bottom of the larynx. There are fifteen to twenty rings in total, separated by narrow intervals. These reinforce the front and sides of the trachea to protect and maintain the airway. In front of the rings lies connective tissue and skin. Several other structures pass or sit over it; 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, and the thyroid gland sits below this; with the isthmus of the gland overlying the second to fourth rings. The first tracheal ring is broader than the rest, and often divided at one end; it is connected by the cricotracheal ligament with the lower border of the cricoid cartilage, and is sometimes blended with the next cartilage down. The last cartilage is thick and broad in the middle, due to its lower border being prolonged into a triangular hook-shaped (uncinate) process, which curves downward and backward between the two bronchi. It ends on each side in an imperfect ring, which encloses the commencement of the bronchus. The cartilage above the last is somewhat broader than the others at its center. 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. The trachealis muscle connects the ends of the incomplete rings and contracts during coughing, reducing the size of the lumen of the trachea to increase the rate of air flow. The esophagus lies posteriorly to the trachea, adjoining along the tracheoesophageal stripe. Circular horizontal bands of fibrous tissue called the annular ligaments of trachea join the tracheal rings together. The cartilaginous rings are incomplete to allow the trachea to collapse slightly so that food can pass down the esophagus. A flap-like epiglottis closes the opening to the larynx during swallowing to prevent swallowed matter from entering 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 isthmus of the thyroid, which connects both wings, lies directly in front, whereas the wings lie on the front and stretch to the side.
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 tracheoesophageal ridges which fuse to form the tracheoesophageal septum and this separates the future trachea from the oesophagus and divides the foregut tube into the laryngotracheal tube. Before the end of the fifth week, the trachea begins to develop from the laryngotracheal tube which develops from the laryngotracheal groove. The first part of the cephalic region of the tube forms the larynx, and the next part forms the trachea. The trachea is no more than 4mm diameter during the first year of life, expanding to its adult diameter by late childhood. The trachea is more mobile and of more variable length, deeper, and smaller in children. Histology
10 X Photograph of a histological sample of a human trachea coloured with H&E stain
The trachea is lined with a layer of pseudostratified ciliated
columnar epithelium. The epithelium contains goblet cells, which are
glandular, modified simple columnar epithelial cells that produce
mucins, the main component of mucus.
A tracheo-oesophageal puncture is a surgically created hole between the trachea and the esophagus in a person who has had a total laryngectomy, (removal of larynx). The purpose of the puncture is to restore a person’s ability to speak after the vocal cords have been removed. Tracheomalacia (weakening of the tracheal cartilage)
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
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.
In invertebrates the open respiratory system is made up of spiracles,
tracheae, and tracheoles that terrestrial arthropods have to transport
metabolic gases to and from tissues. The distribution of spiracles
can vary greatly among the many orders 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. The smallest tubes, tracheoles,
penetrate cells and serve as sites of diffusion for
water, oxygen, and carbon dioxide. 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
A tracheal tube may contain ridge-like circumferential rings of
taenidia in various geometries such as loops or helices. 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 shed during moulting (ecdysis).[citation
Bioengineering and prosthesis
In 2008, a Colombian woman, Claudia Castillo (30), received a trachea
transplant using her own stem cells.
Between 2011 and 2014
Paolo Macchiarini of the Karolinska University
Hospital performed eight operations in which he generated an
artificial trachea from a person's stem cells; four of them at
Karolinska, three in Russia, and one in Illinois. In January 2016
the Swedish television station
The tracheobronchial lymph glands.
Coronal section of larynx and upper part of trachea.
Microscopic cross section of human trachea.
Histology at vetmed.wsu.edu
Atlas image: rsa3p2 at the University of Michigan Health System –
^ a b c d e "Karolinska Institute has 'lost confidence' in Paolo
Macchiarini, says it won't renew his contract". KI. 2016-02-04.
^ a b c d e Gray's Anatomy 2008, p. 1000.
^ Ross, Michael. Histology a text and atlas (5th ed.). Wojciech
Pawlina. p. 617.
^ Mescher AL, "Chapter 17. The Respiratory System" (Chapter). Mescher
AL: Junqueira's Basic Histology: Text & Atlas, 12e: "Archived
copy". Archived from the original on 3 June 2013. Retrieved 24
February 2015. .
^ Antunes, MB; Cohen, NA (February 2007). "Mucociliary clearance—a
critical upper airway host defense mechanism and methods of
assessment". Current Opinion in Allergy and Clinical Immunology. 7
(1): 5–10. doi:10.1097/aci.0b013e3280114eef.
^ Molnar, Heather. "Types of Tracheostomy Tubes".
^ Chiu, T.; Cuevas, D.; Cuevas, L.; Monteiro, C. (1990). "Tracheal
agenesis". Southern Medical Journal. 83 (8): 925–930.
doi:10.1097/00007611-199008000-00018. PMID 2200137.
^ "Slide tracheoplasty". Retrieved 2 October 2015.
^ Xue, B; Liang, B; Wang, S; Zhu, L; Lu, Z; Xu, Z (January 2015).
"One-stage surgical correction of congenital tracheal stenosis
complicated with congenital heart disease in infants and young
children". Journal of Cardiac Surgery. 30 (1): 97–103.
doi:10.1111/jocs.12418. PMID 25109422.
^ a b c d Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The
Vertebrate Body. Philadelphia, PA: Holt-Saunders International.
pp. 336–337. ISBN 0-03-910284-X.
^ Wasserthal, Lutz T. (1998). Chapter 25: The Open
editor-in-chief, Susan Standring ; section editors, Neil R. Borley; et al. (2008). Gray's anatomy : the anatomical basis of clinical practice (40th ed.). London: Churchill Livingstone. ISBN 978-0-8089-2371-8. CS1 maint: Explicit use of et al. (link) CS1 maint: Multiple names: authors list (link) CS1 maint: Extra text: authors list (link) Britton, the editors Nicki R. Colledge, Brian R. Walker, Stuart H. Ralston ; illustrated by Robert (2010). Davidson's principles and practice of medicine (21st ed.). Edinburgh: Churchill Livingstone/Elsevier. ISBN 978-0-7020-3085-7.
v t e
Human systems and organs
Carpus Collar bone (clavicle) Thigh bone (femur) Fibula Humerus Mandible Metacarpus Metatarsus Ossicles Patella Phalanges Radius Skull Tarsus Tibia Ulna Rib Vertebra Pelvis Sternum
Fibrous joint Cartilaginous joint Synovial joint
Muscle Tendon Diaphragm
Artery Vein Lymphatic vessel
Spleen Lymph node
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Lymphoid immune system
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Trachea Bronchus Lung
Salivary gland Tongue
Oropharynx Laryngopharynx Esophagus Stomach
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Uterus Vagina Vulva Ovary Placenta
Scrotum Penis Prostate Testicle Seminal vesicle
Pituitary Pineal Thyroid Parathyroid Adrenal Islets of Langerhans
v t e
Anatomy of the lower respiratory tract
Tracheal rings Annular ligaments Carina
Base Apex Root Hilum
Superior lobe Lingula of left lung Middle lobe of right lung Inferior lobe
Type I Type II
Club cell Goblet cell
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