Lecture 17: THE WORK OF BREATHING Flashcards
What happens during inhalation?
Volume is increasing, pressure inside the lungs is decreasing so that pressure outside is now greater than inside and air rushes in
What happens during exhalation?
Volume is decreasing, pressure inside the lungs is increasing and 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
What must be overcome to take a breath?
Stiffness of the lungs and resistance of the airways to the lungs
What must the lungs do to take in air?
Expand
What holds the lungs in place?
Surface tension
Where does air need to move?
From outside to the alveoli
What is compliance?
The magnitude of the change in lung volume produced by the given change in pressure
What does low compliance of lungs mean?
Stiff lungs so lungs have to do more work to expand
What is pulmonary fibrosis?
Thickening and scarring of the alveolar membranes
What does pulmonary fibrosis do?
Makes the lungs too elastic and hard to expand
What can pulmonary fibrosis arise from?
Chronic inflammation or exposure to industrial chemicals
What are alveoli lined with?
Fluid that exerts surface tension
The wall of the alveoli is…
very thin, enhancing the effect of surface tension and making the lungs less compliant
What must be overcome to expand the lungs?
Surface tension
What does surfactant do?
Reduces surface tension in alveoli and makes them easier to expand
What is surfactant produced by?
Alveolar Type 2 pneumocytes
What is the major constituent of surfactant?
Phospholipids
How does surfactant reduce surface tension?
It reduces the attractive forces between fluid molecules lining alveoli by inserting phospholipids between. This increases compliance and makes the lungs easier to expand
What can lack of surfactant/failure to produce surfactant do?
Lead to stiff lungs
What do premature infants do?
Dont produce surfactant (until 28 weeks) which results in respiratory distress syndrome (RDS)
Where is air conducted?
Through the bronchi and bronchioles which exert force (friction) on the air that must be overcome
Where is most of the resistance to airflow?
In the bronchi
DO the small airways contribute much resistance?
The small airways (terminal and respiratory bronchiole) contribute very little to airways resistance (due to high cross sectional area)
