Thoracic diaphragm
Diaphragm | |
---|---|
musculophrenic artery, inferior phrenic arteries | |
Vein | Superior phrenic vein, inferior phrenic vein |
Nerve | Phrenic and lower intercostal nerves |
Identifiers | |
Latin | diaphragma |
Greek | διάφραγμα |
MeSH | D003964 |
TA98 | A04.4.02.001 |
TA2 | 2327 |
FMA | 13295 |
Anatomical terms of muscle] |
The thoracic diaphragm, or simply the diaphragm (
The term diaphragm in anatomy, created by Gerard of Cremona,[6] can refer to other flat structures such as the urogenital diaphragm or pelvic diaphragm, but "the diaphragm" generally refers to the thoracic diaphragm. 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. There is also speculation that the diaphragm is lower on the other side due to heart's presence.
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.
Structure
The diaphragm is an upward curved, c-shaped structure of
As a dome, the diaphragm has peripheral attachments to structures that make up the abdominal and chest walls. The muscle fibres from these attachments converge in a
The muscle fibres of the diaphragm radiate outward from the central tendon. While the diaphragm is one muscle, it is composed of two distinct muscle regions: the costal, which serves as the driver in the work of breathing, and crural diaphragm, which serves as an "anchor;" attaching the muscle to the lower ribs and lumbar vertebrae. The costal diaphragm is further divided into ventral, medial, and dorsal costal portions. [8][9]
The vertebral part of the diaphragm arises from the crura and arcuate ligaments. Right crus arises from L1-L3 vertebral bodies and their intervertebral discs. Smaller left crus arises from L1, L2 vertebral bodies and their intervertebral discs.
The costal part of diaphragm arises from the lower four ribs (7 to 10) costal cartilages.[8]
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. The central part of the tendon is attached above to pericardium. The both sides of the posterior fibres are attached to paracolic gutters (the curving of ribs before attaching to both sides of the vertebral bodies).[8]
Openings
There are a number of openings in the diaphragm through which structures pass between the thorax and abdomen. There are three large openings — one for the aorta (aortic hiatus),[3] one for the esophagus (esophageal hiatus), and one for the inferior vena cava (the caval opening),[8] as well as a series of smaller openings.[12][13]
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. Surrounded by tendons, the opening is stretched open every time inspiration occurs. However, there has been argument that the caval opening actually constricts during inspiration. 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. The aorta does not pierce the diaphragm but rather passes behind it in between the left and right crus.[citation needed]
There are several structures that pierce through the diaphragm, including:
! Description | Vertebral level | Contents |
---|---|---|
caval opening | T8 | The caval opening passes through the central tendon of the diaphragm. It contains the inferior vena cava,[7] and some branches of the right phrenic nerve.[14] The outermost wall of inferior vena cava is fused with the central tendon.[8] |
esophageal hiatus | T10 | 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,[7] left gastric artery and veins, and lymphatics.[8] |
aortic hiatus | T12 | The aortic hiatus is in the posterior part of the diaphragm, between the left and right crus. It contains the aorta, the thoracic duct and Azygous vein.[14] |
Under the medial lumbocostal arch |
least splanchic nerves[13]
| |
Under the lateral lumbocostal arch |
Subcostal nerve and vessels[8] | |
areolar tissue between the sternal and costal parts (see also foramina of Morgagni ) |
the lymphatics from the abdominal wall and convex surface of the liver[citation needed ]
| |
areolar tissue between the fibers springing from the medial and lateral lumbocostal arches |
This interval is less constant; when this interval exists, the upper and back part of the areolar tissue only.[citation needed ]
|
Nerve supply
The diaphragm is primarily innervated by the
Blood supply
Arteries and veins above and below the diaphragm supply and drain blood.
From above, the diaphragm receives blood from branches of the
The diaphragm drains blood into the
Variation
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.
Development
The thoracic diaphragm develops during
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). 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.
Function
The diaphragm is the main muscle of respiration and functions in breathing. 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. 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.
Cavity expansion happens in two extremes, along with intermediary forms. 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. This is often called
When the diaphragm relaxes (moves in the superior direction), air is exhaled by elastic recoil process of the lung and the tissues lining the thoracic cavity. Assisting this function with muscular effort (called forced
The diaphragm is also involved in non-respiratory functions. It helps to expel
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. [citation needed]
Clinical significance
Paralysis
If either the
Herniation
A
Hernias may also occur as a result of congenital malformation, a
Imaging
Due to its position separating the
An X-ray may also be used to check for herniation.[20]
Significance in strength training
The adoption of a deeper breathing pattern typically occurs during physical exercise in order to facilitate greater oxygen absorption. During this process the diaphragm more consistently adopts a lower position within the body's core. In addition to its primary role in breathing, the diaphragm also plays a secondary role in strengthening the posture of the core. This is especially evident during deep breathing where its generally lower position increases intra-abdominal pressure, which serves to strengthen the lumbar spine.
The key to real core stabilization is to maintain the increased IAP while going through normal breathing cycles. [...] The diaphragm then performs its breathing function at a lower position to facilitate a higher IAP.
better source needed]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. This can be an aid in strength training and other forms of athletic endeavour. For this reason, taking a deep breath or adopting a deeper breathing pattern is typically recommended when lifting heavy weights.
Other animals
This section's factual accuracy is disputed. (August 2011)The existence of a membrane separating the pharynx from the stomach can be traced widely among the
epicardium separates digestive organs from the pharynx and heart, but the anus returns to the upper compartment to discharge wastes through an outgoing siphon.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. Structures in fish, amphibians, reptiles, and birds have been called diaphragms, but it has been argued that these structures are not homologous. For instance, the alligator diaphragmaticus muscle does not insert on the esophagus and does not affect pressure of the lower esophageal sphincter.[26] 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. In birds and mammals, lungs are located above the diaphragm. 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.[citation needed] 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.[24]
However, birds do not have diaphragms. 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. 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. 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. Thus, birds do not have the reciprocal tidal breathing flow of mammals. On careful dissection, around eight air sacs can be clearly seen. They extend quite far caudally into the abdomen.[27]
See also
References
This article incorporates text in the public domain from page 404 of the 20th edition of Gray's Anatomy (1918)
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This article incorporates text from a publication now in the public domain: Chambers, Ephraim, ed. (1728). Cyclopædia, or an Universal Dictionary of Arts and Sciences (1st ed.). James and John Knapton, et al.
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