Breathing

How do internal and external respiration differ?

• External respiration: occurs when gases are exchanged between the pulmonary blood vessels and the alveoli

  • This process is preceded by ventilation, also known as breathing

  • occurs in the lungs 

• Internal respiration: occurs when the blood exchanges gases with the body tissues

  • occurs throughout the body

What process precedes external respiration? Ventilation, also known as breathing.

How does breathing occur?

What muscles are involved in breathing and where are they located?

• Diaphragm: connected to ribs at the bottom of chest cavity

• External intercostal: between the ribs

Muscle contraction → Increase in size of lungs → Decrease in pressure within lungs → Air rushes in (called inspiration)

Muscle relaxation → decrease in size of lungs → increase in pressure within lungs → air rushes out (called expiration)

How is lung capacity determined?

• Tidal volume = the amount of air that is exchanged by the lungs at rest

• Inspiratory reserve volume = the additional amount of air that can be inhaled consciously

• Expiratory reserve volume = the additional amount of air that can be exhaled consciously

• Residual volume = the amount of air remaining in lungs after a forced exhalation

• Vital capacity = amount of air someone can consciously exchange with the environment (inhaling and exhaling)

• Total lung capacity = vital capacity + residual volume (about 6 liters for adult men, 10% less for adult females)

Summary: External respiration is preceded by breathing.  Muscle movements lead to volume and pressure changes, causing air to move in and out.  Total lung capacity can be divided into several partial volumes.