L10. Lung development and surfactant Flashcards
How does surfactant low surface tension in the lung
Surface tension in the lung is made by the attractive intermolecular forces between the liquid lining (at the liquid-gas interface lining) the alveoli.
Surfactant sits at the surface and interferes with these intermolecular attractions. This reduces the pressure required to inflate the lung- energy required to overcome surface tension- therefore improves compliance. Aids fluid balance by reducing tendency of fluid to be sucked into the airspace, host defence, reduce formation and maintenance of liquid plugs and reduction of adhesion in the upper airways.
What is the ratio of components of surfactant
Mixture of 95% phospholipid and 5% protein.
Where/how is surfactant produced
Produced in laminar bodies of type 2 alveolar cell where it is stored in tubular myelin sheets which require SPA, SPB and Ca2+, before being secreted on airway epithelium where SPA, SPB and SPC help to form the phospholipid monolayer
What is the structure and function of phospholipid part of surfactant
Phospholipid: polar, hydrophilic head and non polar, hydophobic tail made of carbon chains.
They have low intermolecular forces and sit at the surface, interfering with surface tension.
What is the structure and function of protein part of surfactant
SP Protein:
-2 large hydrophilic (A and D). Non specific movement of particulate matter towards ciliated regions aided by surface tension gradients (A more than D), SPA and D bind to pathogens to promote the action of macrophages in the immune response and regulation of surfactant synthesis.
-2 small lipophilic (B and C). Breaking up the myelin sheet and stabilising the phospholipid monolayer
What ways can surfactant be degraded/ rate of catabolism
Rate in adults : 3-11 hours, faster in infants.
- Taken up by type 2 cells by endocytosis and reused.
- Can have transport toward ciliated airways, due to surface tension gradients.
- Degradation by extracellular enzymatic activity.
- Macrophage phagocytosis- SPA
- Epithelial reabsorption into the lymph or the blood.
What is laplaces law and its effect on the pressure required to inflate the lung
Pressure inside the alveolus = 2 x surface tension/ radius.
Therefore for a small radius like the alveoli, the pressure to inflate it will increase, and it will be mostly proportional to the surface tension
Describe neonatal respiratory distress syndrome
Premature babies without sufficient pulmonary surfactant in lungs means work of breathing is large. Generating negative pressures in the intrapleural space causes the lungs not to expand but to be teared apart
What is a complication of neonatal respiratory distress syndrome
Bronchopulmonary dysplasia in response to pulmonary epithelium damage due to increased respiratory pressures/ Reactive oxygen species due to O2 therapy
Which germ layers make up the lung airways, parenchyma, and pleura
Lung airways: endodermal primarily
Parenchyma and pleura: mesodermal
What is the time period and main features of the Embryonic period of lung airway
7 weeks. The lung bud arises as a ventral outpouching of primitive oesophagus endoderm, grows downwards and branches 3 times to make the 1,2,3 bronchi.
What is the time period and main features of the Pseudoglandular period of lung airway
5-17 weeks. More branching of the respiratory tree. Now bronchi, bronchioles and terminal bronchioles. No gas exchange
What is the time period and main features of the Canalicular period of lung airway
16-25 week. Each terminal bronchiole –> 2 or more respiratory bronchioles–> 3-6 alveolar ducts lined by cuboidal cells. These cells start to attenuate - become skinny and close together so blood-air barrier is formed. But there is no surfactant
What is the time period and main features of the Saccular period of lung airway
24wk to after birth. Alveolar ducts give rise to primitive alveoli. Increased contact between blood and lymph capillaries and alveoli type 1 cell. Type 2 cells start to develop and produce surfactant
What is the time period and main features of the Alveolar period of lung airway
Late foetal to 8yro. Number of terminal sacs increaes. There is 2ndary septation of the alveoli wall, continued thinning of epithelial lining- increasing SA.
More intimate contact with capillaries.
