Thoracic diaphragm

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This article is about anatomic structure. Thoracic diaphragm_sentence_0

For other uses, see Diaphragm (disambiguation). Thoracic diaphragm_sentence_1

Thoracic diaphragm_table_infobox_0

DiaphragmThoracic diaphragm_header_cell_0_0_0
DetailsThoracic diaphragm_header_cell_0_1_0
OriginThoracic diaphragm_header_cell_0_2_0 Septum transversum, pleuroperitoneal folds, body wallThoracic diaphragm_cell_0_2_1
ArteryThoracic diaphragm_header_cell_0_3_0 Pericardiacophrenic artery, musculophrenic artery, inferior phrenic arteriesThoracic diaphragm_cell_0_3_1
VeinThoracic diaphragm_header_cell_0_4_0 Superior phrenic vein, inferior phrenic veinThoracic diaphragm_cell_0_4_1
NerveThoracic diaphragm_header_cell_0_5_0 Phrenic and lower intercostal nervesThoracic diaphragm_cell_0_5_1
IdentifiersThoracic diaphragm_header_cell_0_6_0
LatinThoracic diaphragm_header_cell_0_7_0 DiaphragmaThoracic diaphragm_cell_0_7_1
GreekThoracic diaphragm_header_cell_0_8_0 διάφραγμαThoracic diaphragm_cell_0_8_1
MeSHThoracic diaphragm_header_cell_0_9_0 Thoracic diaphragm_cell_0_9_1
TA98Thoracic diaphragm_header_cell_0_10_0 Thoracic diaphragm_cell_0_10_1
TA2Thoracic diaphragm_header_cell_0_11_0 Thoracic diaphragm_cell_0_11_1
FMAThoracic diaphragm_header_cell_0_12_0 Thoracic diaphragm_cell_0_12_1

The thoracic diaphragm, or simply the diaphragm (Ancient Greek: διάφραγμα, romanized: diáphragma, lit. Thoracic diaphragm_sentence_2

'partition'), is a sheet of internal skeletal muscle in humans and other mammals that extends across the bottom of the thoracic cavity. Thoracic diaphragm_sentence_3

The diaphragm separates the thoracic cavity, containing the heart and lungs, from the abdominal cavity and performs an important function in respiration: as the diaphragm contracts, the volume of the thoracic cavity increases, creating a negative pressure there, which draws air into the lungs. Thoracic diaphragm_sentence_4

The term diaphragm in anatomy, created by Gerard of Cremona, can refer to other flat structures such as the urogenital diaphragm or pelvic diaphragm, but "the diaphragm" generally refers to the thoracic diaphragm. Thoracic diaphragm_sentence_5

In humans, the diaphragm is slightly asymmetric—its right half is higher up (superior) to the left half, since the large liver rests beneath the right half of the diaphragm. Thoracic diaphragm_sentence_6

There is also a theory that the diaphragm is lower on the other side due to the presence of the heart. Thoracic diaphragm_sentence_7

Other mammals have diaphragms, and other vertebrates such as amphibians and reptiles have diaphragm-like structures, but important details of the anatomy may vary, such as the position of the lungs in the thoracic cavity. Thoracic diaphragm_sentence_8

Structure Thoracic diaphragm_section_0

The diaphragm is a C-shaped structure of muscle and fibrous tissue that separates the thoracic cavity from the abdomen. Thoracic diaphragm_sentence_9

The dome curves upwards. Thoracic diaphragm_sentence_10

The superior surface of the dome forms the floor of the thoracic cavity, and the inferior surface the roof of the abdominal cavity. Thoracic diaphragm_sentence_11

As a dome, the diaphragm has peripheral attachments to structures that make up the abdominal and chest walls. Thoracic diaphragm_sentence_12

The muscle fibres from these attachments converge in a central tendon, which forms the crest of the dome. Thoracic diaphragm_sentence_13

Its peripheral part consists of muscular fibers that take origin from the circumference of the inferior thoracic aperture and converge to be inserted into a central tendon. Thoracic diaphragm_sentence_14

The muscle fibres of the diaphragm emerge from many surrounding structures. Thoracic diaphragm_sentence_15

At the front, fibres insert into the xiphoid process and along the costal margin. Thoracic diaphragm_sentence_16

Laterally, muscle fibers insert into ribs 6–12. Thoracic diaphragm_sentence_17

In the back, muscle fibres insert into the vertebra at T12 and two appendages, the right and left crus, descend and insert into the lumbar vertebrae. Thoracic diaphragm_sentence_18

Right crus arises from L1-L3 their intervertebral discs. Thoracic diaphragm_sentence_19

Left crus from L1, L2 their intervertebral discs. Thoracic diaphragm_sentence_20

There are two lumbocostal arches, a medial and a lateral, on either side. Thoracic diaphragm_sentence_21

Crura and central tendon Thoracic diaphragm_section_1

The left and right crura are tendons that blend with the anterior longitudinal ligament of the vertebral column. Thoracic diaphragm_sentence_22

The central tendon of the diaphragm is a thin but strong aponeurosis near the center of the vault formed by the muscle, closer to the front than to the back of the thorax, so that the posterior muscular fibers are the longer. Thoracic diaphragm_sentence_23

Openings Thoracic diaphragm_section_2

There are a number of openings in the diaphragm through which structures pass between the thorax and abdomen. Thoracic diaphragm_sentence_24

There are three large openings—the aortic, the esophageal, and the caval opening—plus a series of smaller ones. Thoracic diaphragm_sentence_25

The inferior vena cava passes through the caval opening, a quadrilateral opening at the junction of the right and middle leaflets of the central tendon, so that its margins are tendinous. Thoracic diaphragm_sentence_26

Surrounded by tendons, the opening is stretched open every time inspiration occurs. Thoracic diaphragm_sentence_27

However, there has been argument that the caval opening actually constricts during inspiration. Thoracic diaphragm_sentence_28

Since thoracic pressure decreases upon inspiration and draws the caval blood upwards toward the right atrium, increasing the size of the opening allows more blood to return to the heart, maximizing the efficacy of lowered thoracic pressure returning blood to the heart. Thoracic diaphragm_sentence_29

The aorta does not pierce the diaphragm but rather passes behind it in between the left and right crus. Thoracic diaphragm_sentence_30

The thoracic spinal levels at which the three major structures pass through the diaphragm can be remembered by the number of letters contained in each structure: Thoracic diaphragm_sentence_31

Thoracic diaphragm_unordered_list_0

  • Vena Cava (8 letters) – Passes through the diaphragm at T8.Thoracic diaphragm_item_0_0
  • Oesophagus (10 letters) – Passes through the diaphragm at T10.Thoracic diaphragm_item_0_1
  • Aortic Hiatus (12 letters) – Descending aorta passes through the diaphragm at T12.Thoracic diaphragm_item_0_2

Thoracic diaphragm_table_general_1

Openings through the diaphragm and their contentThoracic diaphragm_table_caption_1
! DescriptionThoracic diaphragm_header_cell_1_0_0 Vertebral levelThoracic diaphragm_header_cell_1_0_1 ContentsThoracic diaphragm_header_cell_1_0_2
caval openingThoracic diaphragm_cell_1_1_0 T8Thoracic diaphragm_cell_1_1_1 The caval opening passes through the central tendon of the diaphragm. It contains the inferior vena cava, and some branches of the right phrenic nerve.Thoracic diaphragm_cell_1_1_2
esophageal hiatusThoracic diaphragm_cell_1_2_0 T10Thoracic diaphragm_cell_1_2_1 The esophageal hiatus is situated in the posterior part of the diaphragm, located slightly left of the west central tendon through the muscular sling of the right crus of the diaphragm.

It contains the esophagus, and anterior and posterior vagal trunks.Thoracic diaphragm_cell_1_2_2

aortic hiatusThoracic diaphragm_cell_1_3_0 T12Thoracic diaphragm_cell_1_3_1 The aortic hiatus is in the posterior part of the diaphragm, between the left and right crus.

It contains the aorta and the thoracic duct.Thoracic diaphragm_cell_1_3_2

two lesser apertures of right crusThoracic diaphragm_cell_1_4_0 Thoracic diaphragm_cell_1_4_1 greater and lesser right splanchnic nerves and the azygos veinThoracic diaphragm_cell_1_4_2
two lesser apertures of left crusThoracic diaphragm_cell_1_5_0 Thoracic diaphragm_cell_1_5_1 greater and lesser left splanchnic nerves and the hemiazygos veinThoracic diaphragm_cell_1_5_2
behind the diaphragm, under the medial lumbocostal archThoracic diaphragm_cell_1_6_0 Thoracic diaphragm_cell_1_6_1 sympathetic trunkThoracic diaphragm_cell_1_6_2
areolar tissue between the sternal and costal parts (see also foramina of Morgagni)Thoracic diaphragm_cell_1_7_0 Thoracic diaphragm_cell_1_7_1 the superior epigastric branch of the internal thoracic artery and some lymphatics from the abdominal wall and convex surface of the liverThoracic diaphragm_cell_1_7_2
areolar tissue between the fibers springing from the medial and lateral lumbocostal archesThoracic diaphragm_cell_1_8_0 Thoracic diaphragm_cell_1_8_1 This interval is less constant; when this interval exists, the upper and back part of the kidney is separated from the pleura by areolar tissue only.Thoracic diaphragm_cell_1_8_2

Nerve supply Thoracic diaphragm_section_3

The diaphragm is primarily innervated by the phrenic nerve which is formed from the cervical nerves C3, C4 and C5. Thoracic diaphragm_sentence_32

While the central portion of the diaphragm sends sensory afferents via the phrenic nerve, the peripheral portions of the diaphragm send sensory afferents via the intercostal (T5–T11) and subcostal nerves (T12). Thoracic diaphragm_sentence_33

Blood supply Thoracic diaphragm_section_4

Arteries and veins above and below the diaphragm supply and drain blood. Thoracic diaphragm_sentence_34

From above, the diaphragm receives blood from branches of the internal thoracic arteries, namely the pericardiacophrenic artery and musculophrenic artery; from the superior phrenic arteries, which arise directly from the thoracic aorta; and from the lower internal intercostal arteries. Thoracic diaphragm_sentence_35

From below, the inferior phrenic arteries supply the diaphragm. Thoracic diaphragm_sentence_36

The diaphragm drains blood into the brachiocephalic veins, azygos veins, and veins that drain into the inferior vena cava and left suprarenal vein. Thoracic diaphragm_sentence_37

Variation Thoracic diaphragm_section_5

The sternal portion of the muscle is sometimes wanting and more rarely defects occur in the lateral part of the central tendon or adjoining muscle fibers. Thoracic diaphragm_sentence_38

Development Thoracic diaphragm_section_6

The thoracic diaphragm develops during embryogenesis, beginning in the third week after fertilization with two processes known as transverse folding and longitudinal folding. Thoracic diaphragm_sentence_39

The septum transversum, the primitive central tendon of the diaphragm, originates at the rostral pole of the embryo and is relocated during longitudinal folding to the ventral thoracic region. Thoracic diaphragm_sentence_40

Transverse folding brings the body wall anteriorly to enclose the gut and body cavities. Thoracic diaphragm_sentence_41

The pleuroperitoneal membrane and body wall myoblasts, from somatic lateral plate mesoderm, meet the septum transversum to close off the pericardio-peritoneal canals on either side of the presumptive esophagus, forming a barrier that separates the peritoneal and pleuropericardial cavities. Thoracic diaphragm_sentence_42

Furthermore, dorsal mesenchyme surrounding the presumptive esophagus form the muscular crura of the diaphragm. Thoracic diaphragm_sentence_43

Because the earliest element of the embryological diaphragm, the septum transversum, forms in the cervical region, the phrenic nerve that innervates the diaphragm originates from the cervical spinal cord (C3,4, and 5). Thoracic diaphragm_sentence_44

As the septum transversum descends inferiorly, the phrenic nerve follows, accounting for its circuitous route from the upper cervical vertebrae, around the pericardium, finally to innervate the diaphragm. Thoracic diaphragm_sentence_45

Function Thoracic diaphragm_section_7

The diaphragm is the main muscle of respiration and functions in breathing. Thoracic diaphragm_sentence_46

During inhalation, the diaphragm contracts and moves in the inferior direction, enlarging the volume of the thoracic cavity and reducing intra-thoracic pressure (the external intercostal muscles also participate in this enlargement), forcing the lungs to expand. Thoracic diaphragm_sentence_47

In other words, the diaphragm's movement downwards creates a partial vacuum in the thoracic cavity, which forces the lungs to expand to fill the void, drawing air in the process. Thoracic diaphragm_sentence_48

Cavity expansion happens in two extremes, along with intermediary forms. Thoracic diaphragm_sentence_49

When the lower ribs are stabilized and the central tendon of the diaphragm is mobile, a contraction brings the insertion (central tendon) towards the origins and pushes the lower cavity towards the pelvis, allowing the thoracic cavity to expand downward. Thoracic diaphragm_sentence_50

This is often called belly breathing. Thoracic diaphragm_sentence_51

When the central tendon is stabilized and the lower ribs are mobile, a contraction lifts the origins (ribs) up towards the insertion (central tendon) which works in conjunction with other muscles to allow the ribs to slide and the thoracic cavity to expand laterally and upwards. Thoracic diaphragm_sentence_52

When the diaphragm relaxes, air is exhaled by elastic recoil process of the lung and the tissues lining the thoracic cavity. Thoracic diaphragm_sentence_53

Assisting this function with muscular effort (called forced exhalation) involves the internal intercostal muscles used in conjunction with the abdominal muscles, which act as an antagonist paired with the diaphragm's contraction. Thoracic diaphragm_sentence_54

The diaphragm is also involved in non-respiratory functions. Thoracic diaphragm_sentence_55

It helps to expel vomit, feces, and urine from the body by increasing intra-abdominal pressure, aids in childbirth, and prevents acid reflux by exerting pressure on the esophagus as it passes through the esophageal hiatus. Thoracic diaphragm_sentence_56

In some non-human animals, the diaphragm is not crucial for breathing; a cow, for instance, can survive fairly asymptomatically with diaphragmatic paralysis as long as no massive aerobic metabolic demands are made of it. Thoracic diaphragm_sentence_57

Clinical significance Thoracic diaphragm_section_8

Paralysis Thoracic diaphragm_section_9

If either the phrenic nerve, cervical spine or brainstem is damaged, this will sever the nervous supply to the diaphragm. Thoracic diaphragm_sentence_58

The most common damage to the phrenic nerve is by bronchial cancer, which usually only affects one side of the diaphragm. Thoracic diaphragm_sentence_59

Other causes include Guillain–Barré syndrome and systemic lupus erythematosus. Thoracic diaphragm_sentence_60

Herniation Thoracic diaphragm_section_10

Main articles: Hiatus hernia and Congenital diaphragmatic hernia Thoracic diaphragm_sentence_61

A hiatus hernia is a hernia common in adults in which parts of the lower esophagus or stomach that are normally in the abdomen pass/bulge abnormally through the diaphragm and are present in the thorax. Thoracic diaphragm_sentence_62

Hernias are described as rolling, in which the hernia is beside the oesophagus, or sliding, in which the hernia directly involves the esophagus. Thoracic diaphragm_sentence_63

These hernias are implicated in the development of reflux, as the different pressures between the thorax and abdomen normally act to keep pressure on the esophageal hiatus. Thoracic diaphragm_sentence_64

With herniation, this pressure is no longer present, and the angle between the cardia of the stomach and the oesophagus disappear. Thoracic diaphragm_sentence_65

Not all hiatus hernias cause symptoms however, although almost all people with Barrett's oesophagus or oesophagitis have a hiatus hernia. Thoracic diaphragm_sentence_66

Hernias may also occur as a result of congenital malformation, a congenital diaphragmatic hernia. Thoracic diaphragm_sentence_67

When the pleuroperitoneal membranes fail to fuse, the diaphragm does not act as an effective barrier between the abdomen and thorax. Thoracic diaphragm_sentence_68

Herniation is usually of the left, and commonly through the posterior lumbocostal triangle, although rarely through the anterior foramen of Morgagni. Thoracic diaphragm_sentence_69

The contents of the abdomen, including the intestines, may be present in the thorax, which may impact development of the growing lungs and lead to hypoplasia. Thoracic diaphragm_sentence_70

This condition is present in 0.8 - 5/10,000 births. Thoracic diaphragm_sentence_71

A large herniation has high mortality rate, and requires immediate surgical repair. Thoracic diaphragm_sentence_72

Imaging Thoracic diaphragm_section_11

Due to its position separating the thorax and abdomen, fluid abnormally present in the thorax, or air abnormally present in the abdomen, may collect on one side of the diaphragm. Thoracic diaphragm_sentence_73

An X-ray may reveal this. Thoracic diaphragm_sentence_74

Pleural effusion, in which there is fluid abnormally present between the two pleurae of the lungs, is detected by an X-ray of the chest, showing fluid collecting in the angle between the ribs and diaphragm. Thoracic diaphragm_sentence_75

An X-ray may also be used to reveal a pneumoperitoneum, in which there is gas in the abdomen. Thoracic diaphragm_sentence_76

An X-ray may also be used to check for herniation. Thoracic diaphragm_sentence_77

Significance in strength training Thoracic diaphragm_section_12

The adoption of a deeper breathing pattern typically occurs during physical exercise in order to facilitate greater oxygen absorption. Thoracic diaphragm_sentence_78

During this process the diaphragm more consistently adopts a lower position within the body's core. Thoracic diaphragm_sentence_79

In addition to its primary role in breathing, the diaphragm also plays a secondary role in strengthening the posture of the core. Thoracic diaphragm_sentence_80

This is especially evident during deep breathing where its generally lower position increases intra-abdominal pressure, which serves to strengthen the lumbar spine. Thoracic diaphragm_sentence_81

Therefore, if a person's diaphragm position is lower in general, through deep breathing, then this assists the strengthening of their core during that period. Thoracic diaphragm_sentence_82

This can be an aid in strength training and other forms of athletic endeavour. Thoracic diaphragm_sentence_83

For this reason, taking a deep breath or adopting a deeper breathing pattern is typically recommended when lifting heavy weights. Thoracic diaphragm_sentence_84

Other animals Thoracic diaphragm_section_13

The existence of a membrane separating the pharynx from the stomach can be traced widely among the chordates. Thoracic diaphragm_sentence_85

Thus the model organism, the marine chordate lancelet, possesses an atriopore by which water exits the pharynx, which has been claimed (and disputed) to be homologous to structures in ascidians and hagfishes. Thoracic diaphragm_sentence_86

The tunicate epicardium separates digestive organs from the pharynx and heart, but the anus returns to the upper compartment to discharge wastes through an outgoing siphon. Thoracic diaphragm_sentence_87

Thus the diaphragm emerges in the context of a body plan that separated an upper feeding compartment from a lower digestive tract, but the point at which it originates is a matter of definition. Thoracic diaphragm_sentence_88

Structures in fish, amphibians, reptiles, and birds have been called diaphragms, but it has been argued that these structures are not homologous. Thoracic diaphragm_sentence_89

For instance, the alligator diaphragmaticus muscle does not insert on the esophagus and does not affect pressure of the lower esophageal sphincter. Thoracic diaphragm_sentence_90

The lungs are located in the abdominal compartment of amphibians and reptiles, so that contraction of the diaphragm expels air from the lungs rather than drawing it into them. Thoracic diaphragm_sentence_91

In birds and mammals, lungs are located above the diaphragm. Thoracic diaphragm_sentence_92

The presence of an exceptionally well-preserved fossil of Sinosauropteryx, with lungs located beneath the diaphragm as in crocodiles, has been used to argue that dinosaurs could not have sustained an active warm-blooded physiology, or that birds could not have evolved from dinosaurs. Thoracic diaphragm_sentence_93

An explanation for this (put forward in 1905), is that lungs originated beneath the diaphragm, but as the demands for respiration increased in warm-blooded birds and mammals, natural selection came to favor the parallel evolution of the herniation of the lungs from the abdominal cavity in both lineages. Thoracic diaphragm_sentence_94

However, birds do not have diaphragms. Thoracic diaphragm_sentence_95

They do not breathe in the same way as mammals and do not rely on creating a negative pressure in the thoracic cavity, at least not to the same extent. Thoracic diaphragm_sentence_96

They rely on a rocking motion of the keel of the sternum to create local areas of reduced pressure to supply thin, membranous airsacs cranially and caudally to the fixed-volume, non-expansive lungs. Thoracic diaphragm_sentence_97

A complicated system of valves and air sacs cycles air constantly over the absorption surfaces of the lungs so allowing maximal efficiency of gaseous exchange. Thoracic diaphragm_sentence_98

Thus, birds do not have the reciprocal tidal breathing flow of mammals. Thoracic diaphragm_sentence_99

On careful dissection, around eight air sacs can be clearly seen. Thoracic diaphragm_sentence_100

They extend quite far caudally into the abdomen. Thoracic diaphragm_sentence_101

See also Thoracic diaphragm_section_14

This article uses anatomical terminology. Thoracic diaphragm_sentence_102

Thoracic diaphragm_unordered_list_1

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: diaphragm.