View source for Thorax

{{short description|Frontal part of an animal's body, between its head and abdomen}}
{{About|the anatomy concept}}
{{Redirect|Chest|the furniture used for storage|Chest (furniture)|other uses|Chest (disambiguation)}}
{{Infobox anatomy
| Name = Thorax<br>Chest
| Latin = thorax
| Greek = θώραξ
| Image = Chest.jpg
| Caption = X-ray image of the human chest showing the internal anatomy of the [[rib cage]], [[lungs]] and [[heart]] as well as the inferior thoracic border–made up of the [[thoracic diaphragm|diaphragm]].
| Width =
| Image2 = Surface projections of the organs of the trunk.png
| Caption2 = Surface projections of the organs of the [[Torso|trunk]], with the thorax or chest region seen stretching down to approximately the end of the [[oblique lung fissure]] anteriorly, but more deeply its lower limit rather corresponds to the upper border of the liver.
| Precursor =
| System =
| Artery =
| Vein =
| Nerve =
| Lymph =
}}
The '''thorax''' ({{plural form}}: '''thoraces''' or '''thoraxes''')<ref>{{Cite web |title=Definition: Thorax |url=https://www.oxfordlearnersdictionaries.com/definition/english/thorax |website=Oxford Learner's Dictionaries}}</ref> or '''chest''' is a part of the [[anatomy]] of mammals and other [[tetrapod]] animals located between the [[neck]] and the [[abdomen]].<ref>{{DorlandsDict|nine/000957692|thorax}}</ref><ref>{{MeSH name|Thorax}}</ref>

In [[insect]]s, [[crustacean]]s, and the extinct [[trilobite]]s, the thorax is one of the three main [[Tagma (biology)|divisions]] of the body, each in turn composed of multiple segments.

The human thorax includes the [[thoracic cavity]] and the [[thoracic wall]]. It contains organs including the [[heart]], [[lungs]], and [[thymus]] gland, as well as muscles and various other internal structures. The chest may be affected by many diseases, of which the most common symptom is [[chest pain]].

[[File:Male Thorax.jpg|thumb|22-year-old male chest and nipples]]

==Etymology==
The word thorax comes from the [[Ancient Greek|Greek]] θώραξ ''thṓrax'' "[[breastplate]], [[cuirass]], [[corslet]]"<ref>[https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dqw%2Frac θώραξ],
Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus Digital Library</ref> via {{langx|la|thorax}}.<ref>{{cite book |article=thorax, n.|publisher=Oxford University Press|title=Oxford English Dictionary|language=en|url=https://www.oed.com/view/Entry/200980?redirectedFrom=thorax+}}</ref>

==Humans==
===Structure===
In humans and other [[Hominidae|hominid]]s, the thorax is the chest region of the body between the [[neck]] and the [[abdomen]], along with its internal [[Organ (anatomy)|organs]] and other contents. It is mostly protected and supported by the [[rib cage]], [[vertebral column|spine]], and [[pectoral girdle|shoulder girdle]].

====Contents====
{{Main|Thoracic cavity}}
[[File:Chest labeled.png|thumb|right|An [[X-ray]] of a human chest area, with some structures labeled]]
The contents of the thorax include the [[heart]] and [[lungs]] (and the [[thymus]] gland); the [[Pectoralis major muscle|major]] and [[Pectoralis minor muscle|minor]] pectoral muscles, [[trapezius muscle]]s, and [[neck]] muscle; and internal structures such as the [[thoracic diaphragm|diaphragm]], the [[esophagus]], the [[trachea]], and a part of the [[sternum]] known as the [[xiphoid process]]. Arteries and veins are also contained – ([[aorta]], [[superior vena cava]], [[inferior vena cava]] and the [[pulmonary artery]]); [[bone]]s (the shoulder socket containing the upper part of the [[humerus]], the [[scapula]], [[Human sternum|sternum]], [[Thoracic vertebrae|thoracic portion of the spine]], [[collarbone]], and the rib cage and [[floating rib]]s).

External structures are the [[Human skin|skin]] and [[nipple]]s.

====Chest====
In the [[human body]], the region of the thorax between the [[neck]] and [[Thoracic diaphragm|diaphragm]] in the front of the body is called the chest. The corresponding area in an animal can also be referred to as the chest.

The shape of the chest does not correspond to that part of the [[thoracic skeleton]] that encloses the [[heart]] and [[lungs]]. All the breadth of the shoulders is due to the shoulder girdle, and contains the [[axilla]]e and the heads of the [[humerus|humeri]]. In the middle line the [[suprasternal notch]] is seen above, while about three fingers' breadth below it a transverse ridge can be felt, which is known as the [[sternal angle]] and this marks the junction between the manubrium and body of the [[sternum]]. Level with this line the second ribs join the sternum, and when these are found the lower ribs can often be counted. At the lower part of the sternum, where the seventh or last true ribs join it, the [[ensiform cartilage]] begins, and above this there is often a depression known as the pit of the [[stomach]].

====Bones====
The bones of the thorax, called the "thoracic skeleton" is a component of the [[axial skeleton]].

It consists of the [[ribs]] and [[Human sternum|sternum]]. The ribs of the thorax are numbered in ascending order from 1–12. 11 and 12 are known as floating ribs because they have no anterior attachment point in particular the cartilage attached to the sternum, as 1 through 7 are, and therefore are termed "floating".<ref>{{Citation |last=Safarini |first=Omar A. |title=Anatomy, Thorax, Ribs |date=2024 |work=StatPearls |url=https://www.ncbi.nlm.nih.gov/books/NBK538328/ |access-date=2024-08-21 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=30855912 |last2=Bordoni |first2=Bruno}}</ref> Whereas ribs 8 through 10 are termed false ribs as their costal cartilage articulates with the costal cartilage of the rib above. The thorax bones also have the main function of protecting the heart, lungs, and major blood vessels in the thorax area, such as the [[aorta]].

====Landmarks====
The anatomy of the chest can also be described through the use of [[anatomical landmark]]s. The [[nipple]] in the male is situated in front of the fourth rib or a little below; vertically it lies a little external to a line drawn down from the middle of the [[clavicle]]; in the female it is not so constant. A little below it the lower limit of the great pectoral muscle is seen running upward and outward to the axilla; in the female this is obscured by the [[breast]], which extends from the second to the sixth rib vertically and from the edge of the sternum to the mid-axillary line laterally. The female nipple is surrounded for half an inch by a more or less pigmented disc, the [[areola]]. The apex of a normal heart is in the fifth left intercostal space, three and a half inches from the mid-line.

===Clinical significance===
[[File:High-resolution computed tomographs of a normal thorax (thumbnail).jpg|thumb|link=Commons:Scrollable high-resolution computed tomography images of a normal thorax|[[High-resolution computed tomography|High-resolution computed tomograph]]s of a normal thorax, taken in the [[Axial plane|axial]], [[Coronal plane|coronal]] and [[sagittal plane]]s, respectively. {{noprint|[[Commons:Scrollable high-resolution computed tomography images of a normal thorax|Click here to scroll through the image stacks.]]}} This type of investigation can be used for detecting both acute and chronic changes in the [[lung]] parenchyma.]]

Different types of [[diseases]] or conditions that affect the chest include [[pleurisy]], [[flail chest]], [[atelectasis]], and the most common condition, chest pain. These conditions can be hereditary or caused by [[birth defects]] or [[Trauma (medicine)|trauma]]. Any condition that lowers the ability to either breathe deeply or to [[cough]] is considered a chest disease or condition.

====Injury====
Injury to the chest (also referred to as chest trauma, thoracic injury, or thoracic trauma) results in up to {{sfrac|1|4}} of all deaths due to [[Physical trauma|trauma]] in the United States.<ref>Shahani, Rohit, MD. (2005). [http://www.emedicine.com/med/topic2916.htm Penetrating Chest Trauma]. ''eMedicine''. Retrieved 2005-02-05.</ref>

The major [[pathophysiology|pathophysiologies]] encountered in blunt chest trauma involve derangements in the flow of air, blood, or both in combination. Sepsis due to leakage of alimentary tract contents, as in esophageal perforations, also must be considered. Blunt trauma commonly results in chest wall injuries (e.g., rib fractures). The pain associated with these injuries can make breathing difficult, and this may compromise ventilation. Direct lung injuries, such as pulmonary contusions (see the image below), are frequently associated with major chest trauma and may impair ventilation by a similar mechanism.

====Pain====
[[Chest pain]] can be the result of multiple issues, including [[respiratory]] problems, [[digestion|digestive]] issues, and [[musculoskeletal]] complications. The pain can trigger cardiac issues as well. Not all pain that is felt is associated with the heart, but it should not be taken lightly either. Symptoms can be different depending on the cause of the pain.<ref>{{usurped|1=[https://web.archive.org/web/20141216225857/http://chestdiseases.net/ Chest Diseases]}} Retrieved on 2010-1-26</ref> While cardiac issues cause feelings of sudden pressure in the chest or a crushing pain in the back, neck, and arms, pain that is felt due to noncardiac issues gives a burning feeling along the digestive tract or pain when deep breaths are attempted. Different people feel pains differently for the same condition. Only a patient truly knows if the symptoms are mild or serious.

Chest pain may be a symptom of [[myocardial infarctions]] ('heart attack'). If this condition is present in the body, discomfort will be felt in the chest that is similar to a heavy weight placed on the body. Sweating, shortness of breath, [[lightheadedness]], and [[Cardiac dysrhythmia|irregular heartbeat]] may also be experienced. If a heart attack occurs, the bulk of the damage is caused during the first six hours, so getting the proper treatment as quickly as possible is important. Some people, especially those who are elderly or have diabetes, may not have typical chest pain but may have many of the other symptoms of a heart attack. It is important that these patients and their caregivers have a good understanding of heart attack symptoms.

=====Non-cardiac causes=====
As with a heart attack, not all chest pain is caused by conditions involving the [[heart]]. Chest wall pain can be experienced after an increase in activity. Persons who add exercise to their daily routine generally feel this type of pain at the beginning.{{citation needed|date=May 2022}} It is important to monitor the pain to ensure that it is not a sign of something more serious. Pain can also be experienced in persons who have an upper respiratory [[infection]], which is accompanied by a fever and cough. [[Shingles]] is another viral infection that can give symptoms of chest or rib pain before a rash develops. Injuries to the rib cage or sternum is also a common cause of chest pain. It is generally felt when deep breaths are taken or during a cough.

====Atelectasis====
Another non-cardiac cause of chest pain is [[atelectasis]]. It is a condition that occurs when a portion of the lung collapses from being airless. When bronchial tubes are blocked, this condition develops and causes patients to feel shortness of breath. The most common cause of atelectasis is when a bronchi that extends from the windpipe is blocked and traps air. The blockage may be caused by something inside the [[bronchus]], such as a plug of mucus, a [[tumour]], or an inhaled foreign object such as a coin, piece of food, or a toy.<ref>[http://www.merck.com/mmhe/sec04/ch048/ch048a.html Atelectasis] Lung and Airway Disorders. Retrieved on 2010-1-26</ref> It is possible for something outside of the bronchus to cause the blockage.

====Pneumothorax====
[[Pneumothorax]] is the condition where air or gas can build up in the [[pleural]] space. It can occur without a known cause or as the result of a lung disease or acute lung injury.<ref>[https://www.nhlbi.nih.gov/health/pleural-disorders Pleurisy] Lung Diseases. Retrieved on 2010-1-26</ref> The size of the pneumothorax changes as air or gas builds up, so a medical procedure can release the pressure with a needle. If it is untreated, blood flow can be interrupted and cause a drop in blood pressure known as tension pneumothorax. It is possible for smaller cases to clear up on their own. Symptoms of this condition are often felt only on one side of the lung or as a shortness of breath.
===Images===
<gallery widths="200px">
File:3D CT of thorax, annotated.jpg|[[Volume rendering]] of a [[high resolution computed tomography]] of the thorax. The anterior thoracic wall, the airways and the pulmonary vessels anterior to the [[root of the lung]] have been digitally removed in order to visualize the different levels of the [[pulmonary circulation]].
File:Slide2DENNO.JPG|Thorax. Anterior view.
File:Slide2DENNNO.JPG|Thorax. Anterior view.
File:Deutsche Jugendmeisterschaften Gerätturnen männlich Training at Internationales Deutsches Turnfest Berlin 2017 (Martin Rulsch) 0831.jpg|Clearly visible thorax of an [[Artistic gymnastics|artistic gymnast]].
</gallery>

==Tetrapods==
In [[mammal]]s, the thorax is the region of the body formed by the [[sternum]], the thoracic [[vertebra]]e, and the [[rib]]s. It extends from the neck to the [[thoracic diaphragm|diaphragm]], and does not include the [[upper limb]]s. The [[heart]] and the [[lung]]s reside in the [[thoracic cavity]], as well as many [[blood vessel]]s. The inner organs are protected by the [[rib cage]] and the sternum. Thoracic vertebrae are also distinguished in [[bird]]s, but not in [[reptile]]s.

==Arthropods==
{{main|Thorax (insect anatomy)}}
{{multiple image
| align = right
| direction = horizontal
| image1 =Trilobite sections-en.svg
| width1 = 220
| caption1 = The trilobite body is divided into three major sections, a cephalon with eyes, mouthparts and sensory organs such as antennae, a thorax of multiple similar segments (that in some species allowed them to roll up into a ball), and a pygidium, or tail section.
| image2 = Scheme ant worker anatomy-en.svg
| width2 =300
| caption2 = In the worker ant, the abdomen consists of the [[propodeum]] fused to the thorax and the [[metasoma]], itself divided into the narrow [[petiole (insect)|petiole]] and bulbous [[gaster (insect anatomy)|gaster]].
}}
In [[insect]]s, [[crustacean]]s, and the extinct [[trilobite]]s, the thorax is one of the three main [[Tagma (biology)|divisions]] of the creature's body, each of which is in turn composed of multiple segments. It is the area where the [[insect wing|wings]] and legs attach in insects, or an area of multiple articulating plates in trilobites. In most insects, the thorax itself is composed of three segments; the [[prothorax]], the [[mesothorax]], and the [[metathorax]]. In extant insects, the prothorax never has wings, though legs are always present in adults; wings (when present) are restricted to at least the mesothorax, and typically also the metathorax, though the wings may be reduced or modified on either or both segments. In the [[apocrita]]n [[Hymenoptera]], the first abdominal segment is fused to the metathorax, where it forms a structure known as the [[propodeum]]. Accordingly, in these insects, the functional thorax is composed of four segments, and is therefore typically called the [[mesosoma]] to distinguish it from the "thorax" of other insects.

Each thoracic segment in an insect is further subdivided into various parts, the most significant of which are the dorsal portion (the [[notum]]), the lateral portion (the [[Pleuron (insect)|pleuron]]; one on each side), and the ventral portion (the [[sternum (arthropod)|sternum]]). In some insects, each of these parts is composed of one to several independent exoskeletal plates with membrane between them (called [[sclerite]]s), though in many cases the sclerites are fused to various degrees.

==See also==
{{Anatomy-terms}}
* [[Pectus carinatum]]
* [[Pectus excavatum]]
* [[Thoracic cavity]]
* [[Cardiothoracic surgery]]

== References ==
{{Reflist}}

==External links==
{{Wiktionary}}
{{Commons category}}
* {{cite web | author=Sam Gon III | title=A guide to the Orders of Trilobites | url=http://www.trilobites.info/index.htm | access-date=August 23, 2005}}

{{Human regional anatomy}}
{{Muscles of thorax and back}}
{{Arteries of thorax}}
{{Muscles of the thorax and back}}
{{Thoracic lymph nodes}}
{{Authority control}}

[[Category:Animal anatomy]]
[[Category:Thorax (human anatomy)| ]]
[[Category:Trilobite anatomy]]