2017 Group Project 5
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Lungs
An introduction to the lungs...
On this page, we will be exploring the development of the lungs through the stages of embryonic growth.
Lung Anatomy
Lung Histology
Developmental origin overview
Brief overview of development of lung
More detailed overview in lung development stages
The Respiratory Zone
The Terminal Bronchioles
Alveolar ducts
Alveoli
The Conducting Zone
The Lung Development Stages
Developmental timeline
Structure of respiratory network
Physiologically, the organ can be divided into two parts:
The Conducting system – consists of all tubular structures including the larynx, trachea and bronchi. (image)
The Functional unit – An alveolus containing specialised epithelial cells where gas exchange occurs.
By week 8 of development, the lungs are in the development of the pseudoglandular stage (refer to developmental timeline). The three germ layers formed in gastrulation all contribute to the development of the lung, including signalling for a cascade of events as well as branching of the bronchiole.
A three-dimensional fractal model of an airway tree with 54 611 branches; branches distal to different segmental bronchi are shown in same colour as segmental bronchus. (a) Anterior view and (b) right lateral view
Developmental signalling processes
The development of a mammalian lung is a multi-step and highly complex process involving signalling pathways. This hierarchy process, referred to as branching morphogenesis is essential to generate numerous airways and gas-exchanging units, and is critically regulated by interactions of signalling pathways in the epithelium and mesenchyme.
Several growth factors and chemical signals have been identified to influence lung development. The main signalling molecules include:
1. Fibroblast Growth Factor (FGF10) - serves as a signalling cue for epithelium outgrowth in the mesenchyme.
2. Sonic Hedgehog (SHH) - produced in the epitheliumand is involved in regulating FGF10 expression, leading to the intertubular mesenchyme to facilitate growth and formation of epithelial buds.
3. Heparan Sulfate Glycosaminoglycans (HS-GAG) - interacts with SHH in order to produce epthelial cells and lung morphogenesis. There is still a lack of understanding in the role that HS plays in mammalian lung development.
Early buds formation is dependent on reciprocal interactions between the lung epithelium and mesenchyme mediated by distinct signalling.
Distal signalling centre is marked by the expression of fibroblast growth factor FGF10 in the mesenchyme. FGF10 signalling serves as cue for epithelium outgrowth.
The conducting system
Branching of lungs Different types of branching - domain branching, planar bifurcation, trifurcation, orthogonal bifurcation.
The mammalian lung develops through branching morphogenesis.
Alveolus: the functional unit
How the alveoli work. Cell types Maturation and development Surfactant - where cells are derived from (macrophages, type 1 and type 2 pneumocytes) Lungs become fully developed within the mother, however they do not function until birth.
At the end of the conducting system, are sac-like structures known as alveoli, which are assist in gas in exchange.
Current understandings and areas of research
include any relevant articles
Review and research articles
Movies
Animal models
Abnormal development
Premature Birth
Lobar Emphysema
Congenital Diaphragmatic Hernia
Azygos lobe
Meconium Aspiration Syndrome
Newborn Respiratory Distress Syndrome
Surfactant Metabolism
Bronchopulmonary Dysplasia
Lung Agenesis
Cystic Fibrosis
CHAOS (Congenital High Airway Obstruction Syndrome)
CPAM (Congenital Pulmonary Airway Malformation)
Lung Cardiovasculature
Future questions
Glossary
References
- ↑ Gilbert SF. Developmental Biology. 6th edition. Sunderland (MA): Sinauer Associates; 2000. Comparative Embryology. Available from: https://www.ncbi.nlm.nih.gov/books/NBK9974/