Respiration and Structures

• Respiration: Exchange of gases between the atmosphere, blood, and cells. The combination of 3 processes required for respiration to occur is; Ventilation (breathing), External (pulmonary) respiration, and Internal (tissue) respiration.

• Organization: Two ways to organize the system:

  • Structurally: Upper respiratory system (nose, pharynx, and associated structures), Lower respiratory system (larynx, bronchi, and lungs)

  • Functionally:  Conducting zone and respiratory zone.

• Conducting Zone: Trachea, Bronchi, Bronchioles, and Terminal Bronchioles. It Transports air to the lungs, and can be used to warm, humidify, filter, and clean the air as well as produced mucus and traps small particles and cilia away from the lungs. Also used in voice production.’

• Terminal and Respiratory zones: Respiratory bronchioles, Alveolar ducts and Alevolar sacs.

• Inhalation/Ventilation:

  • During inhalation, the diaphragm contracts, and the external intercostals contract. The chest cavity expands as well as the volume of the lungs. The alveolar pressure drops below the atmospheric pressure and air flows into the lungs in response to the pressure gradient during deep inhalation, the scalene and sternocleidomastoid muscles expand the chest further, thereby creating a greater drop in alveolar pressure.

  • At rest when the diaphragm is relaxed the alveolar pressure is equal to atmospheric pressure so there is no airflow, but when exhalation occurs then the diaphragm relaxes and the external intercostals relax. The chest and lungs as such also recoil and the chest cavity contracts with the alveolar pressure increasing above atmospheric pressure so air flows out.

  • The alveolar surface is lined by type 1 and type 2 cells. The thin cytoplasm of the type 1 cell is ideal for gas diffusion whereas the type 2 cell is important for the production of surfactant which decreases the surface tension of the alveolus.