The respiratory system does not carry out its physiological function (gas exchange) prenatally and remain entirely fluid-filled until birth (More? Birth Notes). At birth, fluid in the upper respiratory tract is expired and fluid in the lung aveoli is rapidly absorbed this event has also been called "dewatering of the lung".
The lung epithelia has to now rapidly change from its prenatal secretory function to that of fluid absorbtion. This is initiated by a late fetal change in alveolar epithelial cell (AEC) chloride and fluid secretion to sodium and fluid absorption. This absorption requires sodium-potassium ATPase (Na-K-ATPase) together with apical sodium entry mechanisms (Epithelial Sodium Channels, ENaC). Fetal thyroid hormone is thought to have a hormonal role in this developmental switch (More? Endocrine Thyroid)
During the late fetal period regular fetal breathing movements (FBM) also occur preparing both the skeletomuscular sysyem and lungs mechanically for respiration.
These changes and pressure also lead to the pulmonary sytem becoming activated and changes in the circulatory shunting that existed before birth (More? Heart Notes) .
It is also at this stage as the lungs begin to function that some functional abnormalities become obvious (More? Respiratory Abnormalities)
Several different mammalian models (rabbit, sheep, rat) and methods (imaging) have been developed to study this physiological process at birth.
Postnatally the lungs continue to grow (add new aveoli and branches) for another 8+ years.
Page Links: Introduction | Some Recent Findings | The First Breath | Epithelial Sodium Channel | Rabbit Model | | Persistent Pulmonary Hypertension of the Newborn | Glossary | References
Elias N, Rafii B, Rahman M, Otulakowski G, Cutz E, O'Brodovich H. The role of alpha-, beta-, and gamma-ENaC subunits in distal lung epithelial fluid absorption induced by pulmonary edema fluid. Am J Physiol Lung Cell Mol Physiol. 2007 Sep;293(3):L537-45.
Wilson SM, Olver RE, Walters DV. Developmental regulation of lumenal lung fluid and electrolyte transport. Respir Physiol Neurobiol. 2007 Dec 15;159(3):247-55.
Hooper SB, Kitchen MJ, Wallace MJ, Yagi N, Uesugi K, Morgan MJ, Hall C, Siu KK, Williams IM, Siew M, Irvine SC, Pavlov K, Lewis RA. Imaging lung aeration and lung liquid clearance at birth. FASEB J. 2007 Oct;21(12):3329-37.
(More? see Reviews)
The exchange of lung fluid for air leads to:
fall in pulmonary vascular resistance
increase in pulmonary blood flow
thinning of pulmonary arteries (stretching as lungs increase in size)
blood fills the alveolar capillaries
In the heart, pressure in the right side of the heart decreases and pressure in the left side of the heart increases (more blood returning from pulmonary).
Elias N, Rafii B, Rahman M, Otulakowski G, Cutz E, O'Brodovich H. The role of alpha-, beta-, and gamma-ENaC subunits in distal lung epithelial fluid absorption induced by pulmonary edema fluid. Am J Physiol Lung Cell Mol Physiol. 2007 Sep;293(3):L537-45.
"To study the role of subunits of the epithelial Na(+) channel (ENaC) in the phenomena, we cultured explants from the distal lungs of 16-day gestational age wild-type (WT) or alpha-, beta-, or gamma-ENaC knockout or heterozygote (HT) mice. ...We conclude that beta- and gamma-, but not alpha-, ENaC subunits are essential for EF to exert its maximal effect on net fluid absorption by distal lung epithelia."
The rabbit has been used in several studies as a model of changes that occur in the respiratory system at birth.
Hooper SB, Kitchen MJ, Wallace MJ, Yagi N, Uesugi K, Morgan MJ, Hall C, Siu KK, Williams IM, Siew M, Irvine SC, Pavlov K, Lewis RA. Imaging lung aeration and lung liquid clearance at birth. FASEB J. 2007 Oct;21(12):3329-37.
"The air/liquid interface moved toward the distal airways only during inspiration, with little proximal movement during expiration, indicating that trans-pulmonary pressures play an important role in airway liquid clearance at birth. Using these imaging techniques, the dynamics of lung aeration and the critical role it plays in regulating the physiological changes at birth can be fully explored."
A 1980's study has compared changes in liquid clearance of full term rabbits (31 days gestation) born vaginally or by cesarean section.
Bland RD, McMillan DD, Bressack MA, Dong L. Clearance of liquid from lungs of newborn rabbits. J Appl Physiol. 1980 Aug;49(2):171-7.
"pulmonary blood volume of both groups of rabbits increased soon after birth
extravascular lung water per gram of dry lung tissue was greater at birth in rabbits born by cesarean section than in those born vaginally
extravascular lung water did not begin to decrease in either group of animals until 30-60 min postnatally, after which it decreased progressively for 24 h
the rate of fluid clearance and pattern of puddling around pulmonary vessels was similar in both groups of rabbits, with maximal perivascular cuffs 30 min after birth, followed by diminution of cuff size as the lungs shed water."
A condition occuring in 2 to 6/1000 live births due to the failure of one of the prenatal circulatory shunts, the ductus arteriosus, to close. This is related to lung and pulmonary development but related more to cardiovascular fetal/neonatal development and transition. (More? Cardiovascular Notes) There are several known factors which can influence the development of PPHN (hypoplastic lungs, hyaline membrane disease, transient tachypnoea of the newborn, congenital pneumonia and Meconium Aspiration Syndrome). Links: NZ - Newborn Services Clinical Guideline | KidsHealth - PPHN
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.
Wilson SM, Olver RE, Walters DV. Developmental regulation of lumenal lung fluid and electrolyte transport. Respir Physiol Neurobiol. 2007 Dec 15;159(3):247-55.
Olver RE, Walters DV, M Wilson S. Developmental regulation of lung liquid transport. Annu Rev Physiol. 2004;66:77-101.
Barker PM, Olver RE. Invited review: Clearance of lung liquid during the perinatal period. J Appl Physiol. 2002 Oct;93(4):1542-8.
Strang LB. Changes in the lungs at birth. Sci Basis Med Annu Rev. 1965;:202-16.
Articles
Hooper SB, Kitchen MJ, Wallace MJ, Yagi N, Uesugi K, Morgan MJ, Hall C, Siu KK, Williams IM, Siew M, Irvine SC, Pavlov K, Lewis RA. Imaging lung aeration and lung liquid clearance at birth. FASEB J. 2007 Oct;21(12):3329-37.
Bland RD, McMillan DD, Bressack MA, Dong L. Clearance of liquid from lungs of newborn rabbits. J Appl Physiol. 1980 Aug;49(2):171-7.
Search PubMed Now: fetal lung from secretion to absorption | lung dewatering | fetal respiratory movements
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Old Glossary
Home Page
Embryo stages
Fetal Dev
System Notes
Animal Dev
Acknowledgements
Introduction
Abnormalities
Stage 13/14
Stage 22
Stage 22 Selected
Respiratory Birth
Molecular
Text only
WWW Links
Movies
Audio
Class Notes
Serial Images
K12 Students
Abnormal
Prenatal Diagnosis
Animal Embryos
Mechanisms
Molecular
Histology
Statistics
History
Site Map
Glossary
OMIM
School of Med Sci
UNSW Medicine
University of NSW
UNSW Cell Biology
NCBI Books
New 2010 Site
Enjoyed this site? Visit the New 2010 Site!
The respiratory system does not carry out its physiological function (gas exchange) prenatally and remain entriely fluid-filled until birth. At birth, fluid in the upper respiratory tract is expired and fluid in the lung aveoli is rapidly absorbed. Postnatally the lungs continue to grow for another 8+ years.
Thirdly, lung development goes through 4 stages, the final stage (type 2 surfactant secretion) only occurs in the final weeks of development. This means that premature infants have respiratory difficulties due to the still immature respiratory system. More recently, this has been treated in these infants with humidicribs and various surfactant therapies.
Educational Use Only.
Please email Dr Mark Hill if you wish to make a comment about this current project.