[#5] MECÂNICA RESPIRATÓRIA: TENSÃO SUPERFICIAL E SURFACTANTE | MK Fisiologia

Summary

In this video, Miriam explains the concept of surface tension in the lungs, focusing on how it impacts lung mechanics. Surface tension in the liquid lining the alveoli contributes significantly to lung elastic recoil, influencing both lung compliance and elastance. The video highlights the role of surfactant in reducing surface tension, facilitating lung expansion during inhalation, and preventing alveolar collapse. The absence of surfactant, as seen in neonatal respiratory distress syndrome, makes lung expansion more difficult. Overall, the video provides a detailed explanation of the respiratory mechanics, particularly the crucial role of surfactant in maintaining lung function.

Takeaways

• 😀 The video explains how surface tension in the liquid lining the alveolar walls plays a key role in lung mechanics, particularly in terms of lung compliance and elastance.
• 😀 Lung compliance refers to the lungs' ability to stretch, while elastance refers to their ability to recoil. These two are inversely proportional.
• 😀 The main factor determining lung recoil is surface tension, not just elastic fibers in the lung tissue. Surface tension within alveoli contributes significantly to the lung's elastic properties.
• 😀 Surface tension is a physical phenomenon observed at the interface between a liquid and air. Molecules of water form hydrogen bonds, creating a cohesive force that causes the liquid surface to contract.
• 😀 The LaPlace equation describes the relationship between surface tension and pressure in spheres, stating that smaller alveoli have higher pressure due to greater surface tension.
• 😀 In normal lung function, smaller alveoli do not collapse because of mechanical interdependence between alveoli and the presence of surfactant.
• 😀 Surfactant, a substance produced by type II alveolar cells, reduces surface tension in the alveoli, making it easier to expand the lungs during inhalation.
• 😀 The surfactant is made up of phospholipids and proteins. Its hydrophobic tails interact with air, while the hydrophilic heads interact with the water in the alveolar lining, reducing surface tension.
• 😀 Without surfactant, as seen in neonatal respiratory distress syndrome, surface tension increases, elastance rises, and lung compliance decreases, making it harder for the lungs to expand.
• 😀 Surfactant also helps to prevent fluid buildup in the alveoli and stabilizes alveolar size, preventing collapse when alveolar radius decreases or increases, ensuring proper gas exchange.

Q & A

What is surface tension and how does it relate to lung function?

Surface tension is a physical phenomenon that occurs at the liquid-air interface, where the molecules at the surface are not surrounded by other liquid molecules in the upward direction, creating a force that tries to minimize the surface area. In the lungs, this surface tension in the alveolar liquid layer contributes to lung recoil (elasticity), influencing pulmonary compliance and elastance.

What is the relationship between compliance and elastance in the lungs?

Compliance is the ability of the lungs to stretch or expand, while elastance is the ability of the lungs to return to their original shape after being stretched. They are inversely related: higher compliance means lower elastance, making it easier to stretch the lungs, and vice versa.

How does surface tension affect lung compliance?

Surface tension increases the elastic recoil of the lungs, making it harder for the lungs to expand. Therefore, greater surface tension reduces lung compliance, making it more difficult to stretch the lungs during inspiration.

What role do elastic fibers play in lung recoil?

Elastic fibers, particularly those made of elastin, contribute to the lung's ability to return to its resting state after being stretched. However, their contribution to lung recoil is smaller than the contribution of surface tension, which plays a greater role in determining lung elastance.

How does the Laplace law relate to lung function?

The Laplace law describes the relationship between surface tension and pressure in spherical structures. It states that pressure inside a sphere is directly proportional to the surface tension and inversely proportional to the radius. In the lungs, smaller alveoli have higher internal pressures due to their smaller radius, making them more prone to collapse without surfactant.

What is the function of surfactant in the alveoli?

Surfactant reduces surface tension in the alveoli by interacting with the water molecules at the surface. This reduction in surface tension makes it easier for the lungs to expand during inspiration, thereby increasing lung compliance and preventing alveolar collapse.

Why is surfactant essential for newborns, especially premature ones?

Premature newborns may lack sufficient surfactant, which leads to higher surface tension in the alveoli, making it harder for their lungs to expand. This results in respiratory distress syndrome, where the baby has difficulty breathing due to the reduced compliance of the lungs.

How does surfactant prevent alveolar collapse?

Surfactant stabilizes alveolar size by reducing surface tension. When the radius of an alveolus decreases, surfactant concentration at the surface increases, reducing surface tension and preventing the alveolus from collapsing. This allows alveoli of different sizes to remain open and functional.

What would happen if surfactant were absent in the lungs?

In the absence of surfactant, surface tension in the alveoli would increase, making it much harder for the lungs to expand. This would result in reduced lung compliance, increased work for respiratory muscles, and difficulty with ventilation, as seen in neonatal respiratory distress syndrome.

How does surface tension in the alveoli affect the pressure in the lungs?

Surface tension in the alveoli increases the pressure inside smaller alveoli, as per the Laplace law. This pressure difference can lead to the collapse of smaller alveoli into larger ones unless counteracted by surfactant, which helps maintain stable pressures across alveoli of varying sizes.