Physiology, Lung

Excerpt

The lungs are the foundational organs of the respiratory system, whose most basic function is to facilitate gas exchange from the environment into the bloodstream. Oxygen gets transported through the alveoli into the capillary network, where it can enter the arterial system, ultimately perfuse tissue. The respiratory system is composed primarily of the nose, oropharynx, larynx, trachea, bronchi, bronchioles, and lungs. The lungs further divide into individual lobes, which ultimately subdivide into over 300 million alveoli. The alveoli are the primary location for gas exchange. The diaphragm is the primary respiratory muscle and receives innervation by the nerve roots of C3, C4, and C5 via the phrenic nerve. The external intercostals are inspiratory muscles used primarily during exercise and respiratory distress. The significant lung volumes/capacities and their definitions are listed below.

1. Inspiratory reserve volume (IRV): Volume that can be breathed after a normal inspiration

2. Tidal volume (TV): Volume inspired and expired with each breath

3. Expiratory reserve volume (ERV): Volume that can be expired after a normal breath

4. Residual volume (RV): Volume remaining in the lung after maximal expiration (cannot be measured by spirometry)

5. Inspiratory capacity (IC): Volume that can be breathed after normal exhalation

6. Functional residual capacity (FRC): Volume remaining in the lungs after normal expiration

7. Vital capacity (VC): Maximum volume able to be expired after maximal inspiration

8. Total lung capacity (TLC): Volume of air in the lungs after maximal inspiration

9. Forced expiratory volume (FEV1): Volume that can be expired in 1 second of maximum forced expiration