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
Pulmonary fibrosis is an example of a
restrictive lung disease
Obstructive pulmonary diseases
Respiration is more difficult and takes longer
Asthma
- Obstructive pulmonary disease
- Airways are narrowed by bronchoconstriction
Chronic bronchitis
- Obstructive pulmonary disease
- Plugs of mucus and inflammatory swelling of bronchial mucosa obstructs the airways
Anatomic dead space
Where inspired gas that does not get down to the site of gas exchange in the alveoli and remains in the conducting airways, not available for gas exhange
Tidal volume components
- 450 mL enter alveoli
- 150 mL is old air from dead space
- 300 mL fresh air from atmosphere
Ventilation rate
Volume of air moved into and out of the lungs per unit time
Ventilation rate can be expressed as
- Minute ventilation - total rate of air movement in and out of lungs
- Alveolar ventilation - corrects for anatomic dead space
Minute ventilation equation
Tidal volume x respiratory rate
Alveolar ventilation equation
(tidal volume - dead space volume) x respiratory rate
4 factors affecting the diffusion across the respiratory membrane
- Thickness of membrane
- SA of membrane
- Diffusion coefficient
- Partial pressure gradients of o2 and co2
Thickness of membrane normally remains
constant
Thickness of membrane increases with pathological conditions such as
- Pulmonary edema
- Pulmonary fibrosis
- Pneumonia
Surface area of membrane changes
- Increases during exercise
- Normally remains constant
- Decreases during diseases like emphysema
Rate of transfer increases as the diffusion coefficient ____
increase
Diffusion coefficient for CO2 is ____ times that of O2
30
Partial pressure gradients of O2 and CO2 - rate of transfer increases as diffusion partial pressure gradient _______
increases
