Society and HealthThis lecture (These Notes are currently being updated for 2009)
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Related Links: Respiratory Development Notes | eMed Lecture |
To understand the prenatal and postnatal developmental anatomy of human respiratory organs.
External Link: eMed
Slides PDF: SH 2009 Respiratory Development 1 slide/page (view only) | SH 2009 Respiratory Development 4 slides/page (print) | SH 2009 Respiratory Development 6 slides/page (print)
1. Embryonic origin of respiratory components (tract, lungs, diaphragm, muscles)
2. Key stages in respiratory development.
3. Time course of respiratory development.
4. Respiration at birth.
5. Postnatal development of respiration.
6. Developmental abnormalities.
1. Embryonic origin of respiratory components (tract, lungs, diaphragm, muscles)
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Note: Click on the small cross-section extract to view entire section.
Links: 3D Respiratory Development - Stage 22 | 3D Respiratory Development - Stage 22 | Respiratory Development - Stage 13 | Respiratory Development - Stage 22 | Selected - Stage 22 | Respiratory Development - Diaphragm |
* Week 4 - laryngotracheal groove forms on floor foregut.
* Week 5 - left and right lung buds push into the pericardioperitoneal canals (primordia of pleural cavity)
* Week 6 - descent of heart and lungs into thorax. Pleuroperitoneal foramen closes.
* Week 7 - enlargement of liver stops descent of heart and lungs.
* Month 3-6 - lungs appear glandular, end month 6 alveolar cells type 2 appear and begin to secrete surfactant.
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Five elements contribute to the diaphragm. septum transversum - central tendon 3rd to 5th somite - musculature of diaphragm (More? Somites) ventral pleural sac - connective tissue mesentry of oesophagus - connective tissue around oesophasus and IVC (More? Gastrointestinal Tract) pleuroperitoneal membranes - connective tissue around central tendon |
Adult Diaphragm
Adult 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.
Links: Diaphragm Innervation
Fetal Respiratory Movements (FRM) or Fetal Breathing Movements (FBM)
* 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.
Lung Fluid
* epithelium switches from secretion to absorption in preparation and adaptation to air breathing.
* lung not the amniotic sac is the source of liquid that fills the lumen of the developing lung, by chloride secretion across the respiratory epithelium
* both the rate and volume of liquid formation within the lumen of the fetal lung decrease near gestational term
* labor may aid lung liquid removal during birth
Lungs continue to grow
Muscular changes with growth.
Links: Postnatal Development - Respiratory | 69. Management of Bronchiolitis in Infants and Children
Links: Respiratory Development - Abnormalities | 69. Management of Bronchiolitis in Infants and Children
Developmental Overview
* Week 4 - laryngotracheal groove forms on floor foregut.
* Week 5 - left and right lung buds push into the pericardioperitoneal canals (primordia of pleural cavity)
* Week 6 - descent of heart and lungs into thorax. Pleuroperitoneal foramen closes.
* Week 7 - enlargement of liver stops descent of heart and lungs.
* Month 3-6 - lungs appear glandular, end month 6 alveolar cells type 2 appear and begin to secrete surfactant.
* Month 7 - respiratory bronchioles proliferate and end in alveolar ducts and sacs.
Lung Development histological periods
*embryonic - formation of the trachea, the main bronchi, the five lobes and by the end of this stage, the 18 major lobules.
* 5-17 week pseudoglandular because the epithelial tubules are surrounded by thick mesenchymal tissue.
* 16-25 week canalicular - acinar structures consist of respiratory bronchioles, alveolar ducts, and primordial alveoli.
* 24-40 week terminal sac - acinar tubules dilate and the walls thin leading to an in increased gas exchanging surface area
* late fetal - 18 years alveolar and vascular maturation
Diaphragm 5 elements contribute to the diaphragm
* septum transversum- central tendon
* 3rd to 5th somite- musculature of diaphragm
* ventral pleural sac- connective tissue
* mesentry of oesophagus- connective tissue around oesophasus and IVC
* pleuroperitoneal membranes- connective tissue around central tendon
Blood Supply
* pulmonary system not "functional" until after birth
* 6th aortic arch arteries generate pulmonary arteries
* veins drain into pulmonary vein then left atrium
* branches from dorsal aorta generate bronchial arteries
Splanchnic Mesoderm (mesenchyme)
* cartilage for bronchi and bronchiole
* pulmonary smooth muscles
* connective tissue
* capillaries
* visceral pleura (parietal pleura is formed by mesoderm of the thoracic cavity body wall)
Innervation
* vagus nerve (cranial nerve X, CNX) visceral afferents and efferents for lower respiratory tract
* autonomic fibers from parasympathetic fibers and sympathetic chains
UNSW Embryology
Embryo stages | Fetal Dev | Dev Notes 1 | Dev Notes 2 | System Notes | Timeline of Human Development
Respiratory Histology: Blue Histology - Respiratory System
Embryo Images: Embryo Images Online | Early Cell Populations and Establishment of Body Form | Germ Layers and Initial Gastrulation (Week 3) | Form Changes (Week 3)
Links: Journals | Online Textbooks | Search Textbooks | PubMed | | Search PubMed | Glossary
NIH Genes & Disease
Developmental Biology (6th ed) Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000.
Molecular Biology of the Cell (4th Edn) Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter. New York: Garland Publishing; 2002.
Health Services/Technology Assessment Text (HSTAT) Bethesda (MD): National Library of Medicine (US), 2003 Oct. 69. Management of Bronchiolitis in Infants and Children
Search Textbooks: respiratory development
Search PubMed: term= respiratory+development Search Entrez Databases:respiratory+development
Use the alphabetical list below to find definitions of terms that are new to you.
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
antenatal before birth.
alveoli number at birth from 20 - 50 million and eventually in the adult 300 million.
Bronchopulmonary dysplasia (BPD) the most common serious sequela of premature birth.
Bronchiolitis is a viral infection of the lower respiratory tract and most common lower respiratory tract infection in infants. Respiratory syncytial virus (RSV) is responsible for 70 percent of all cases overall and Parainfluenza, adenovirus and influenza account for most of the remaining cases. HSTAT Management of Bronchiolitis in Infants and Children
Chronic obstructive pulmonary disease (COPD) causes include smoking (85–90 percent of all cases), genetic factors (alpha-1 antitrypsin deficiency), passive smoking (children), occupational exposures, air pollution, and hyperresponsive airways. HSTAT Management of Acute Exacerbations of Chronic Obstructive Pulmonary Disease
Clara cells
Congenital Diaphragmatic Hernia (CDH) disorder with an incidence of 1 in 2500 live births.
fetal breathing-like movements (FBMs)
glucocorticoid treatment antenatal therapy to promote the maturation of the human fetal lung. Given as a synthetic glucocorticoid between 24 and 32 weeks of pregnancy to promote lung maturation in fetuses at risk of preterm delivery.
lamellar bodies the storage form of surfactant in type II alveolar cells, seen as centrically layered "packages" of phospholipid. A count of lamellar bodies can be used as an assay for measuring fetal lung maturity.
maternal diabetes if not controlled in pregnancy may delay fetal pulmonary maturation.
Persistent Pulmonary Hypertension of the Newborn (PPHN) serious newborn condition due to due to the failure of closure one of the prenatal circulatory shunts, the ductus arteriosus. Occurs in about 1-2 newborns per 1000 live births and results in hypoxemia. (More? Respiratory Development - Birth)
Pharyngitis inflammation of the pharynx involving lymphoid tissues of the posterior pharynx and lateral pharyngeal bands.
pneumocyte or alveolar type I and type II cells.
pulmonary hypoplasia can be due to anencephaly, renal hypoplasia or abnormalities of the thoracic cage
pulmonary neuroendocrine cells (PNEC) single or innervated clusters of cells (neuroepithelial bodies) that line the airway epithelium, thought to have a role in regulating fetal lung growth and differentiation. At birth may also act as airway oxygen sensors involved in newborn adaptation. These cells synthesis and release amine (serotonin, 5-HT) and a several neuropeptides (bombesin).
Respiratory distress syndrome (RDS) due to a surfactant deficiency at birth, particulary in preterm birth.
secondary alveolar septa formed during the alveolar stage and are formed by projections of connective tissue and a double capillary loop.
surfactant produced by alveolar type II cells is a mixture of lipids and proteins that both maintains alveolar integrity and plays a role in the control of host defense and inflammation in the lung.
Surfactant therapy
thyroid hormone involved in the regulation of fetal lung development.
vascular endothelial growth factor (VEGF) a secreted growth factor acting through receptors on endothelial cells to regulate vasculogenesis through their development, growth and function.
Movie of Human Embryo Growth (this shows a human embryo growing, all images are to scale)
Movie of Mouse Embryo Growth (this shows a mouse embryo growing)
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Welcome to a Lecture and Practical class in introducing Embryology to you in the new medical curriculum!
This lecture is going to take you briefly through human development. These concepts will later be built upon and revisited in BGD and throughout your Medicine program.
The common problem for students is to know "to what depth" they should study development. The answer lies in "introduction". This is an overview, look at the Aim and Concepts sections and can you understand these on teh basis of teh lecture and practical?
Embryoplogy has many dynamic processes, transient structures and many very specific terms. Start by getting a timeline of developmental events before we get into specific features later in your program.
For new terms or concepts that you don't understand use the Glossary link or Search UNSW Embryology window.
This will be followed by a practical class (links on left) to reinforce these concepts and explore human development for yourself. (More ? Practical 15).
Concepts you learn in this current class will be built upon in future laboratories and lectures.
These notes and linked materials have been prepared for Educational purposes only.
Please email Dr Mark Hill if you wish to make a comment about this current project.
