Lecture 31: Respiraton 2, 3, and 4 Flashcards
In order for inspiration to occur, the lungs must be able to expand when stretched, thus have high
compliance
In order for expiration to occur, lungs must get smaller when stretching force is released, thus have
elasticity
The tendency to get smaller is aided by what within the alveoli
surface tension forces
Compliance/distensibility
The ease with which the lungs can expand under pressure
Lung compliance can be measured as
change in lung volume
A given transpulmonary pressure will cause
greater or lesser expansion, depending on the compliance of the lungs
Compliance of lungs is reduced by factors that
produce a resistance to distension
Pulmonary fibrosis
Infiltration of lung tissue with connective tissue
Decreases lung compliance
Elasticity
Refers to the tendency of a structure to return to it’s initial size after being distended
Why are the lungs elastic?
High content of elastin proteins
Since the lungs are normally stuck to the chest wall, they are always in a state of
elastic tension
The elastic tension ____ during inspiration
increases
Elastic tension is reduced by ____ ____ during expiration
elastic recoil
Tidal volume
the amount of air moved into and out of the lungs during a single respiratory cycle
Forces that act to reduce distension include
- Elastic resistance
- Surface tension exerted by fluid in the alveoli
The most important determinant of lung compliance is
Surface tension at the air-water interphases in the alveoli
Surface tension
the attractive forces between the water molecules in the lipid film that lines each alveolus
Surface tension is responsible for a two fold effect
- Liquid layer opposes expansion of alveolus because the surface water molecules are being pulled apart
- Liquid sa tends to become as small as possible because surface water molecules try to get as close together as possible
Conclusions of surface tension
- Reduces size of alveolus
2. Would be so great that the lungs would collapse if the alveolus were lined with water alone
Pulmonary surfactant
- A complex mixture of lipids and proteins secreted by type II alveolar cells
- Counteracts surface tension of the liquid lining alveoli by interspersing between water molecules
Two benefits of pulmonary surfactant
- Increases pulmonary compliance, reducing the work of the inflating lungs
- Reduces tendency of lungs to recoil, so they don’t collapse as readily
Inadequate production of pulmonary surfactant results in
Difficulty breathing due to low lung compliance
When does cortisol production increase
during pregnancy
Restrictive lung diseases
Alveoli are stiff, expansion is restricted, all volumes and capacities are less than normal