L26. Physiology - Mechanics of Breathing I

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Questions and Answers

What is the role of the type-II alveolar cells?

Facilitating gas exchange

Phagocytizing particulate matter

Providing structural support to alveoli

Secreting surfactant (correct)

How does surface tension affect the behavior of liquid molecules at an air-liquid interface?

It creates equal attraction for surface and subsurface molecules.

It results in a net downward pull on surface molecules. (correct)

It allows subsurface molecules to be exposed to air.

It prevents evaporation by trapping air underneath the liquid.

What feature of the alveoli helps to equalize pressure?

Surfactant secretion

Alveolar pores (correct)

Type-I cells

Pulmonary capillaries

Which of the following statements about surface tension is true?

Surface tension reduces the surface area of a liquid. Signup and view all the answers

What is a primary function of the respiratory membrane?

To separate alveoli from blood in capillaries Signup and view all the answers

What occurs to a paper clip when placed on the surface of water?

It remains at the surface due to surface tension. Signup and view all the answers

Which component of the alveoli is primarily involved in reducing surface tension?

Surfactant Signup and view all the answers

What characteristic of surface molecules leads to the phenomenon of surface tension?

Unequal attraction to below and adjacent molecules Signup and view all the answers

What is the primary role of surfactant in lung physiology?

Reduces surface tension in the alveoli Signup and view all the answers

How does the compliance of a saline-inflated lung compare to that of an air-inflated lung?

It is higher due to lower surface tension Signup and view all the answers

According to LaPlace's Law, what effect does radius have on pressure in the alveoli?

Pressure decreases as radius increases Signup and view all the answers

What would likely happen to lung compliance in the absence of surfactant?

Compliance would be reduced Signup and view all the answers

What does the hysteresis observed in air-inflated lungs indicate?

A difference in pressure during inhalation and exhalation Signup and view all the answers

Which of the following statements about surface tension in the alveoli is true?

It accounts for 1/3 of the elastic recoil of the lung Signup and view all the answers

What is the major component of pulmonary surfactant?

Phospholipids Signup and view all the answers

What is one of the functions of surfactant in the alveoli?

To stabilize alveolar size Signup and view all the answers

Why does a saline-inflated lung exhibit no hysteresis?

Saline provides a constant surface tension Signup and view all the answers

What effect does decreasing surface tension have on the work of breathing?

It decreases the work of breathing Signup and view all the answers

What is the effect of surfactant on the surface tension in the alveoli?

It decreases the surface tension in smaller alveoli more than in larger ones. Signup and view all the answers

According to Laplace's Law, how does the radius of an alveolus affect intraluminal pressure?

Decreased radius leads to increased pressure. Signup and view all the answers

What is a consequence of not having surfactant in alveoli?

Gas flows from larger alveoli to smaller alveoli. Signup and view all the answers

How does the concentration of surfactant change with alveolar size?

Smaller alveoli concentrate surfactant at the air-water interface. Signup and view all the answers

What happens to the intraluminal pressure when surfactant is present?

Intraluminal pressure decreases significantly in smaller alveoli. Signup and view all the answers

What occurs to a collapsed alveolus (atelectatic) when surfactant is present?

It can reinflate due to pressure changes from surfactant. Signup and view all the answers

What impact does surfactant have on lung compliance?

Surfactant increases lung compliance by reducing surface tension. Signup and view all the answers

Why does gas flow from a smaller alveolus to a larger one in the absence of surfactant?

Higher pressure in the larger alveolus compared to the smaller. Signup and view all the answers

What is the primary role of surfactant in respiratory physiology?

To reduce surface tension, preventing alveolar collapse. Signup and view all the answers

What process describes the entry of surfactant molecules into the surface during expiration?

Adsorption Signup and view all the answers

How is lung compliance calculated?

∆V/∆P Signup and view all the answers

What happens to surfactant molecules during inspiration?

They are separated as the alveolar surface expands Signup and view all the answers

What is the intrapleural pressure at the base of the lung compared to the apex, assuming values of -2 cmH2O and -9 cmH2O respectively?

Less negative at the base Signup and view all the answers

What effect does gravity have on the intrapleural pressure at functional residual capacity?

It pushes the upright lung downward, affecting pressure differentials Signup and view all the answers

What is the transpulmonary pressure at the apex of the lung compared to the base, given values of +9 cmH2O and +2 cmH2O respectively?

Higher at the apex Signup and view all the answers

What occurs to surfactant molecules that are 'squeezed out' during expiration?

They remain associated with the surfactant film. Signup and view all the answers

During a change in lung volume, what does a change in intrapleural pressure from -3 cmH2O to -8 cmH2O indicate?

Lung volume has increased. Signup and view all the answers

If the change in volume is 1 L with a change in pressure of 5 cmH2O, what is the lung compliance?

0.2 L/cmH2O Signup and view all the answers

How does the compliance of the alveoli at the apex of the lung compare to that at the base during respiration?

The compliance at the apex is less than at the base. Signup and view all the answers

Which factor contributes most significantly to decreased compliance in lung function?

High lung volume. Signup and view all the answers

What is the primary effect of obstructive lung disease on pulmonary compliance?

Compliance is increased due to the destruction of elastin and collagen. Signup and view all the answers

At functional residual capacity, which statement is true about the alveoli at different lung regions?

The bottoms of the lungs experience greater changes in volume during inspiration. Signup and view all the answers

Which condition is NOT associated with decreased compliance in the lungs?

Obstructive lung disease. Signup and view all the answers

Study Notes

Mechanics of Breathing

Alveoli are surrounded by elastic fibers and smooth muscle, which allows them to expand and contract with air flow.
Alveolar pores equalize pressure within the alveoli.
Macrophages engulf particulate matter in the alveoli.
The respiratory membrane separates the alveoli from the pulmonary capillaries and consists of type I and type II cells.
Type II cells secrete surfactant, which reduces surface tension and promotes alveolar inflation.

Surface Tension

Surface tension in the alveoli is a force that minimizes the exposed surface area of a liquid.
Surface tension results from the attraction between liquid molecules at the air-liquid interface.
This attraction creates a surface film and causes a net downward pull on the surface molecules.
Surface tension is demonstrated by placing a paper clip on the surface of water; it stays afloat due to this force.

Lung Compliance and Surface Tension

Air-inflated lungs exhibit hysteresis, meaning the path of expiration differs from inspiration.
Air-inflated lungs need higher positive pressures compared to saline-inflated lungs, due to surface tension.
Saline-inflated lungs show higher compliance (greater volume change for a given pressure change) and no hysteresis.
A lung without surfactant has lower compliance than a normal lung, requiring more pressure for inflation.

Surfactant

Surfactant is a phospholipid secreted by type II epithelial cells.
It reduces surface tension, decreases the work of breathing, increases compliance, stabilizes alveolar size and dries the alveoli.
Dipalmitoyl phosphatidylcholine, the major component of surfactant, has hydrophobic and hydrophilic portions, allowing it to orient itself at the air-water interface.

Surfactant and Alveolar Stability

Laplace's Law (P = 2T/r) describes the relationship between intra-alveolar pressure, surface tension, and alveolar radius.
Without surfactant, smaller alveoli have higher intra-alveolar pressure, leading to gas flow from smaller to larger alveoli and atelectasis (collapsed alveoli).
Surfactant lowers surface tension in smaller alveoli, reducing pressure and preventing atelectasis.

Surfactant Concentration and Alveolar Size

Surfactant concentration at the air-water interface is higher in smaller alveoli, minimizing surface tension.
Surfactant molecules are squeezed closer together during expiration, further reducing surface tension.
During inspiration, the molecules separate and re-associate with the film during the next expiration, a process called respreading.

Total Lung Compliance

Lung compliance is the change in lung volume divided by the change in lung distending pressure (CL = ∆V/∆P).
Normal lung compliance is approximately 0.2 L/cm H2O.

Pulmonary Compliance and Gravity

Gravity affects intrapleural pressure and lung compliance.
Intrapleural pressure is less negative at the base of the lung than at the apex due to gravity's downward pull.
This difference in pressure leads to higher transpulmonary pressure at the apex, making the alveoli more distended and less compliant compared to the base.
During inspiration, the volume change at the apex is smaller than at the base for the same change in transpulmonary pressure.

Pulmonary Compliance and Disease States

Emphysema increases compliance by destroying lung elastin and collagen.
Lung compliance is decreased by:
- High lung volume
- Restrictive lung diseases
- Alveolar edema
- Surfactant deficiency

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Description

Explore the critical concepts of alveolar mechanics, including how alveoli function and the role of surface tension in respiratory physiology. This quiz covers topics such as alveolar structure, the significance of surfactant, and the effects of surface tension on lung compliance. Test your understanding of these essential components of the respiratory system.