The major organs of the respiratory system function primarily to
- provide oxygen to body tissues for cellular respiration,
- remove the waste product carbon dioxide, and
- help to maintain acid-base balance.
The cough reflex is mediated by sensory fibres of the vagus nerve, a fundamental component of the autonomic nervous system.
The conducting zone of the respiratory system includes the organs and structures not directly involved in gas exchange.The epithelium contains goblet cells, one of the specialized, columnar epithelial cells that produce mucus to trap debris.
Interestingly, cold air slows the movement of the cilia, resulting in accumulation of mucus that may in turn lead to a runny nose during cold weather.
Serous and mucus-producing cells also secrete the lysozyme enzyme and proteins called defensins, which have antibacterial properties.
The cilia of the respiratory epithelium help remove the mucus and debris from the nasal cavity with a constant beating motion, sweeping materials towards the throat to be swallowed.
The epithelium of the nasal passages, for example, is essential to sensing odors, and the bronchial epithelium that lines the lungs can metabolize some airborne carcinogens.
zone, the respiratory zone includes structures that are directly involved in gas exchange. The respiratory zone begins where the terminal bronchioles join a respiratory bronchiole, the smallest type of bronchiole , which then leads to an alveolar duct, opening into a cluster of alveoli.
An alveolar duct is a tube composed of smooth muscle and connective tissue,
The alveolar wall consists of three major cell types:
- type I alveolar cells, a squamous epithelial cell of the alveoli,
- type II alveolar cells, secretes pulmonary surfactant phospholipids and proteins that reduces the surface tension of the alveoli.
- alveolar macrophages.