Respiratory System - Diaphragm

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Introduction

File:Diaphragm sm.jpg
Adult Diaphragm

The respiratory system does not carry out its physiological function (gas exchange) prenatally and postnatally the lungs continue to grow for another 8+ years. Many other tissues/systems are involved in respiratory function: musculoskeletal (ribs and diaphragm) cardiovascular (pulmonary circulation). The musculoskeletal begins functioning prenatally, the cardiovasular pulmonary circulation is activated and altered postnatally.

The diaphragm along with the ribcage are the musculoskeletal structures that regulate lung inflation. The topic of musculoskeletal development is also covered in a separate set of notes (More? Musculoskeletal System Development).

In humans, the muscles of the diaphragm arise from somite level 3 to 5 (C3 to C5), which also corresponds to the levels of segmental nerves providing innervation of the diaphragm.

Failure of complete diaphragm development can lead to a herniation of abdominal components through channels or gaps in the developing diaphragm into the pleural cavity.

In humans, in the third trimester preparatory fetal respiratory movements occur, which are thought to have a number of roles in late respiratory development.

Respiratory Links: respiratory | Science Lecture | Lecture Movie | Med Lecture | Stage 13 | Stage 22 | upper respiratory tract | diaphragm | Histology | Postnatal | respiratory abnormalities | Respiratory Quiz | Respiratory terms | Category:Respiratory
Historic Embryology  
1902 The Nasal Cavities and Olfactory Structures | 1906 Lung | 1912 Upper Respiratory Tract | 1912 Respiratory | 1914 Phrenic Nerve | 1918 Respiratory images | 1921 Respiratory | 1922 Chick Pulmonary Vessels | 1934 Right Fetal Lung | 1936 Early Human Lung | 1937 Terminal Air Passages | 1938 Human Histology

Diaphragm Components

File:Diaphragm2.jpg Five elements contribute to the diaphragm.

septum transversum - central tendon

3rd to 5th somite - musculature of diaphragm (More? [skmus6.htm Somites])

ventral pleural sac - connective tissue

mesentry of oesophagus - connective tissue around oesophasus and IVC (More? [git.htm Gastrointestinal Tract])

pleuroperitoneal membranes - connective tissue around central tendon

Diaphragm Innervation

File:Image804.gifAdult Cervical Plexus (phrenic nerve shown lower right)
Innervation of the human diaphragm is by the phrenic nerves, arising from the same segmental levels from which the diaphragm skeletal muscles arise, segmental levels C3 to C5.

The paired phrenic nerves are mixed containing motor neurons for the diaphragm and sensory nerves for other abdominal structures (mediastinum, pleura, liver, gall bladder).

Netrin signaling may be important in early phrenic nerve growth, as knockout mice show incomplete phrenic nerve innervation of the diaphragm.

Other respiratory muscles include the intercostals which are innervated by the intercostal nerves arising from segmental levels T1 to T11.

References:

Mantilla CB, Sieck GC. Key aspects of phrenic motoneuron and diaphragm muscle development during the perinatal period. J Appl Physiol. 2008 Jun;104(6):1818-27.

Burgess RW, Jucius TJ, Ackerman SL. Motor axon guidance of the mammalian trochlear and phrenic nerves: dependence on the netrin receptor Unc5c and modifier loci. J Neurosci. 2006 May 24;26(21):5756-66.

 

Fetal Respiratory Movements

Fetal respiratory movements (FRM) or Fetal breathing movements (FBM) are thought to be regular muscular contrations occurring in the third trimester, preparing the respiratory muscular system for neonatal function and to have a role in late lung development.

The majority of FBM research has been carried out in fetal sheep.

Hypoxia, decreased oxygen levels, blocks these movements by inhibition of the brain stem respiratory centres.

Hypercapnia, increased carbon dioxide levels, or acid cerebrospinal fluid perfusion can cause an increase in the regularity and depth of breathing.

Hormones also affect fetal breathing movements: inhibitors of prostaglandin synthetase (indomethacin, meclofenamate or aspirin) induce continuous fetal breathing movements, while prostaglandin E2 arrests fetal breathing.

References:

Savich RD, Guerra FA, Lee CC, Kitterman JA. The effect of fetal breathing movements on pulmonary blood flow in fetal sheep.Pediatr Res. 1994 Apr;35(4 Pt 1):484-9.PMID: 8047386 [PubMed - indexed for MEDLINE]

"FBM do not increase mean blood flow through the left pulmonary artery; thus, it is unlikely that FBM stimulate lung growth through changes in pulmonary blood flow."

Blanco CE. Maturation of fetal breathing activity.Biol Neonate. 1994;65(3-4):182-8. Review.PMID: 8038281 [PubMed - indexed for MEDLINE]

Dawes GS. The central control of fetal breathing and skeletal muscle movements.J Physiol. 1984 Jan;346:1-18. Review.PMID: 6422029 [PubMed - indexed for MEDLINE]

Hypercapnia (Greek, hyper = "above" and kapnos = "smoke") or hypercarbia increased carbon dioxide levels.

 

Abnormalities

Congenital Diaphragmatic Hernia (International Classification of Diseases code 756.6)

Failure of the pleuroperitoneal foramen (foramen of Bochdalek) to close allows viscera into thorax. Intestine, stomach or spleen can enter the pleural cavity, compressing the lung.

Australian national rate (1982-1992) 2.1 - 3.8 /10,000 births. (Congenital Malformations Australia 1981-1992 P. Lancaster and E. Pedisich ISSN 1321-8352)

References:

Gallot D, Boda C, Ughetto S, Perthus I, Robert-Gnansia E, Francannet C, Laurichesse-Delmas H, Jani J, Coste K, Deprest J, Labbe A, Sapin V, Lemery D. Prenatal detection and outcome of congenital diaphragmatic hernia: a French registry-based study. Ultrasound Obstet Gynecol. 2007 Mar;29(3):276-83.

"501 cases of CDH were identified from a total of 1,835,022 live births (2.7/10 000 live births). The overall prenatal detection rate was 54%."

Colvin J, Bower C, Dickinson JE, Sokol J. Outcomes of congenital diaphragmatic hernia: a population-based study in Western Australia. Pediatrics. 2005 Sep;116(3):e356-63.

"Ninety-two percent of postoperative infants survived beyond 1 year of age, as did 80% of infants who reached the surgical referral center. However, only 52% of live-born infants, 32% of all cases, and 16% of all prenatally diagnosed cases survived. Therefore, the overall mortality rate for this condition remains high, despite increased prenatal detection, transfer to tertiary institutions for delivery, and advances in neonatal care, and is influenced significantly by the rate of prenatal termination. In our study, 33% of all cases of CDH and 49% of prenatally diagnosed fetuses underwent elective termination of pregnancy. This large number of fetal terminations confounds the accurate assessment of the true outcomes of this condition."

Search Now: Pubmed - Congenital Diaphragmatic Hernia | OMIM - Congenital Diaphragmatic Hernia

Adult Diaphragm

File:Diaphragm.jpg
viewed from beneath

References

Reviews

Mantilla CB, Sieck GC. Key aspects of phrenic motoneuron and diaphragm muscle development during the perinatal period. J Appl Physiol. 2008 Jun;104(6):1818-27.

Burgess RW, Jucius TJ, Ackerman SL. Motor axon guidance of the mammalian trochlear and phrenic nerves: dependence on the netrin receptor Unc5c and modifier loci. J Neurosci. 2006 May 24;26(21):5756-66.

Articles

Search PubMed Now

Search PubMed Now: diaphragm development | phrenic nerve development | fetal respiratory movements | Pubmed - Congenital Diaphragmatic Hernia | OMIM - Congenital Diaphragmatic Hernia

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Cite this page: Hill, M.A. (2020, March 30) Embryology Respiratory System - Diaphragm. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Respiratory_System_-_Diaphragm

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© Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G