2. Breathing Mechanism: I. The Pathway of Air
Breathing is also known as ventilation
Air outside body  mouth/nose  pharynx (throat)  trachea 
bronchi and bronchial tree  lungs  alveoli (air sacs)  reverse
One inhalation + one exhalation = a respiratory cycle

4. Breathing Mechanism:. II. Inspiration (Inhalation) A
Breathing Mechanism: II. Inspiration (Inhalation) A. Principles of Pressure
Air moves into the lungs via atmospheric pressure (760 mm Hg)
Boyle’s Law: pressure and volume are inversely related

5. Breathing Mechanism: II. Inspiration (Inhalation)

6. Breathing Mechanism:. II. Inspiration (Inhalation) B
Breathing Mechanism: II. Inspiration (Inhalation) B. Resting Inspiration
During resting inspiration, the pressure inside the lungs and alveoli decreases and atmospheric pressure pushes outside air into the airways, using the muscles in the dome-shaped diaphragm
Prior to inspiration, the intra-alveolar pressure is 760 mm Hg

7. Breathing Mechanism:. II. Inspiration (Inhalation) B
Breathing Mechanism: II. Inspiration (Inhalation) B. Resting Inspiration
Atmospheric pressure of
760 mm Hg on outside
Atmospheric pressure of 760 mm Hg
n the inside
When the lungs are at rest, the pressure on the inside of the lungs is equal to the pressure on the outside of the thorax

8. Breathing Mechanism:. II. Inspiration (Inhalation) C
Breathing Mechanism: II. Inspiration (Inhalation) C. Normal Inspiration
Muscle fibers of the diaphragm are stimulated to contract by impulses on the phrenic nerves
Diaphragm moves downward  thoracic cavity enlarges  intra-alveolar pressure decreases  atmospheric pressure forces air into the alveoli
External intercostal muscles and thoracic muscles stimulated to contract, elevating the ribs and the sternum and increasing the size of the thoracic cavity
The intra-alveolar pressure decreases to about 758 mm Hg as the thoracic cavity enlarges, and atmospheric pressure forces air into the airways
Intra-alveolar pressure falls further, and atmospheric pressure forces more air into the alveoli

9. Breathing Mechanism:. II. Inspiration (Inhalation) C
Breathing Mechanism: II. Inspiration (Inhalation) C. Normal Inspiration
Pleural membranes dictate the expansion of lungs during movement of the diaphragm
Separation of the pleural membranes decreases pressure between the membranes, and only a thin film of serous fluid separates the pleura lining the thoracic cavity and the pleura attached to the lungs
Water molecules attract these membranes and each other, holding the two membranes together
When the intercostal muscles move the thoracic wall upward or downward, the pleura of both the thoracic cavity and the lungs move too, expanding the lungs

10. Breathing Mechanism:. II. Inspiration (Inhalation) C
Breathing Mechanism: II. Inspiration (Inhalation) C. Normal Inspiration

11. Breathing Mechanism:. II. Inspiration (Inhalation) C
Breathing Mechanism: II. Inspiration (Inhalation) C. Normal Inspiration
Moist inner membranes of the alveoli have the opposite effect
Attraction of water molecules  surface tension  difficult to inflate alveoli
Alveolar cells synthesize a mixture of lipoproteins called surfactant, which is secreted into alveolar air spaces, preventing collapse and helping to expand the alveoli for inspiration
Rx – Respiratory Distress Syndrome: occurs when premature infants do not produce sufficient surfactant
treated by injection of synthetic surfactant through endotracheal tube and a customized ventilator

12. Breathing Mechanism:. II. Inspiration (Inhalation) D
Breathing Mechanism: II. Inspiration (Inhalation) D. Abnormal Inspiration
Deeper than normal breaths = diaphragm and external intercostal muscles contract more forcefully
Pectoralis minor, sternocleidomastoids, and scalenes also pull thoracic cage further upward and outward, enlarging the thoracic cavity and decreasing the intra-alveolar pressure
Normal inspiration vs. maximal inspiration

13. Breathing Mechanism:. II. Inspiration (Inhalation) D
Breathing Mechanism: II. Inspiration (Inhalation) D. Abnormal Inspiration
Compliance (distensibility): ease with which the lungs expand from pressure changes during breathing
Compliance decreases as lung volume increases
Compliance can also be reduced by obstruction of air passages or destroyed lung tissue

15. Breathing Mechanism: III. Expiration (Exhalation) A. Normal Expiration
The forces that stimulate normal resting expiration are derived from the elastic recoil of lung tissues and abdominal organs and from surface tension
When the diaphragm and external intercostal muscles relax after inspiration, the lungs retract from their expanded state during inspiration to their original shapes
The elastic tissues also cause abdominal organs to revert back to their pre-inspiration shapes, pushing the diaphragm upwards

16. Breathing Mechanism: III. Expiration (Exhalation) A. Normal Expiration
Simultaneously, surface tension between the moist surfaces of the alveolar linings shrinks alveoli
These events eventually increase the alveolar pressure above atmospheric pressure, forcing air inside the lungs out through the respiratory passages
Normal resting inspiration occurs passively without contraction of any muscles
The recoil of elastic fibers in lung tissues decreases the pressure on the pleural cavity, and the pressure between the pleural membranes decreases substantially (4 mm Hg less than atmospheric pressure)

17. Breathing Mechanism:. III. Expiration (Exhalation) B
Breathing Mechanism: III. Expiration (Exhalation) B. Abnormal Expiration
Exhaling more air than normal is accomplished by contracting the posterior internal (expiratory) intercostal muscles, which pull the ribs and sternum downward and inward, increasing the air pressure in the lungs, pushing more air out
The abdominal muscles, such as the internal and external obliques, transversus abdominus, and rectus abdominus also squeeze the abdominal organs inward
The abdominal wall muscles can increase pressure in the abdominal cavity and force the diaphragm against the lungs, pushing additional air out of the lungs

18. Breathing Mechanism:. III. Expiration (Exhalation) B
Breathing Mechanism: III. Expiration (Exhalation) B. Abnormal Expiration

19. Breathing Mechanism:. III. Expiration (Exhalation) B
Breathing Mechanism: III. Expiration (Exhalation) B. Abnormal Expiration
Rx – Pneumothorax: Occurs when atmospheric air enters the pleural cavity after thoracic wall is punctured
May collapse lung(s) and create unnatural space between pleural membranes
Treated by covering the chest wound and impermeable bandage and passing a tube through the thoracic wall into the pleural cavity and applying suction to the tube
The suction reestablishes negative pressure in the cavity and the collapsed lung expands

24. Breathing Mechanism:. IV
Breathing Mechanism: IV. Maladies of the Respiratory System (Irritants)
Rx – Asbestos: a lung irritant derived from a naturally occurring mineral used in buildings and many commercial products
Asbestos fibers, when airborne, can cause scars in the lungs when inhaled
May cause shortness of breath, lung cancer, mesothelioma

25. Breathing Mechanism:. IV
Breathing Mechanism: IV. Maladies of the Respiratory System (Irritants)
Rx – Beryliosis: condition caused from beryllium, an element used in fluorescent powders and metal alloys
Exposure to beryllium may produce an immune response that damages the lungs
Symptoms (latent) include cough, shortness of breath, fatigue, fevers, night sweats, and weight loss
Steroid drug, prednisone, is used to control symptoms
Rx – Extrinsic Allergic Alveolitis: caused by repeatedly inhaling organic dusts
Impairs breathing and causes fevers
Changes shapes of lungs chronically
“Bathtub refinisher's lung,” “maple bark stripper disease,” “popcorn worker’s lung,” “wheat weevil’s disease”

26. Breathing Mechanism: IV. Maladies of the Respiratory System
Rx – Air Pollution: a threat to health when particles are small enough to penetrate alveoli
Kills more than seven million people per year
WHO recommends limiting or avoiding outdoors when micro-particulates exceed 25 micrograms per cubic meter or when air quality index exceeds 200