Lecture 17- The work of breathing Flashcards
What are the four main ‘elements’ of the respiratory system?
- Get air in to the alveoli
- Get it across the capillaries
- Exchange to tissues metabolise and pick up carbon dioxide
- Keep it going via neural connections
Explain the pressure gradient in inhalation…
- Volume is increasing
- Pressure inside the lungs is decreasing
- Pressure outside is now greater than inside, so air rushes in
Explain the pressure gradient in exhalation…
- Volume is decreasing
- Pressure inside the lungs is increasing
- Pressure outside is now lower than inside, so air rushes out
What is the direction of airflow determined by?
- Difference between atmospheric pressure and intrapulmonary pressure.
- Will move from high pressure to low pressure
What are the two opposing forces that need to be overcome in order to take a breath?
- Stiffness of the lungs
- Resistance of the airways to the lungs
What is stiffness in the lungs related to?
Compliance: Defined as the magnitude of the change in the lung volume (ΔV) produced by the given change in the pressure (ΔP)
What happens when the lung has low compliance?
- Stiff lungs
- Need to do more work to expand
- Results in condition called Pulmonary Fibrosis where there is thickening and scarring of the alveolar membranes. Can arise from chronic inflammation or exposure to industrial chemicals
What is a factor that must be overcome to expand the lungs?
- Alveoli are lined with fluid that exert surface tension (means the water has an attractive quality and so droplets stick together)
- Walls of alveoli are very thin, enhancing this effect
- Must overcome surface tension to expand the lungs
What does surfactant do?
- Produced by alveolar type 2 pneumocytes
- Major constituent is phospholipids
- Means the surface tension is lowered as it reduces attractive forces between fluid molecules lining the alveoli
- This therefore makes it easier to increase lung size i.e increased compliance
What is a consequence of not enough surfactant? Who doesn’t produce it?
- Lack of surfactant/ failure to produce adequate surfactant results in stiff lungs
- Premature infants don’t produce surfactant and this results in respiratory distress syndrome
Explain why resistance of the airways to the lungs is a factor in how able we are to take a breath?
- Need to move air from outside to the alveoli
- Air is conducted through the bronchi and bronchioles
- Exert force (friction) on the air that must be overcome
What happens when the alveoli collapse with regards to surface tension?
Surface tension increases so lungs become less compliant
What is the equation that describes the relationship between resistance and the lumen size of the bronchi?
R= 1/r^4
What is the main area of resistance in the tree?
- The bronchi
- The smaller airways (terminal and respiratory bronchi contribute very little airway resistance due to having high cross sectional area)
Which of the following statements about the work of
breathing is NOT Correct?
A. The chest and lungs expand during inhalation.
B. The alveoli release surfactant to overcome surface
tension from the surrounding fluid.
C. Low compliance of the lungs allows them to more
easily fill with air.
D. The respiratory tract exerts frictional force on inhaled
air.
E. Most of the airway resistance is in the bronchi.
C. Low compliance of the lungs allows them to more
easily fill with air.
