Respiratory System Help

By — McGraw-Hill Professional
Updated on Aug 18, 2011


All cells require a continuous supply of oxygen (O2) and must continuously eliminate a metabolic waste product, carbon dioxide (CO2). On the macroscopic level, the term respiration simply means ventilation, or breathing. On the cellular level, it refers to the processes by which cells utilize O2, produce CO2, and convert energy into useful forms.

Components of the Respiratory System

The major passages of the respiratory system are the nasal cavity, pharynx, larynx, and trachea. Within the lungs, the trachea branches into bronchi, bronchioles, and finally pulmonary alveoli. While the primary function of the respiratory system is exchange of gasses for cellular metabolism, portions of the respiratory system also function in sound production, abdominal compression, and coughing and sneezing. The conducting division of the respiratory system includes all cavities and structures that transport gases to and from the pulmonary alveoli.

Nasal Cavity

Structures: nasal superior septum; middle and inferior nasal conchae.

Tissues: pseudostratified ciliated columnar epithelium; olfactory epithelium

Warms and moistens the inspired air, also functions in olfaction.


Nasopharynx: auditory (eustachian) canals, uvula, pharyngeal tonsils

Oropharynx: palatine and lingual tonsils

Laryngeopharynx: larynx

The oropharynx and laryngopharynx have respiratory and digestive functions, while the nasopharynx serves only the respiratory system.


Structures: anterior thyroid cartilage, epiglottis, cricoid cartilage, arytenoids cartilages, cuneiform and corniculate cartilages, and the glottis. The larynx forms the entrance into the trachea. Its primary function is to prevent food or fluid from entering the trachea and lungs during swallowing. A secondary function is sound production.

Trachea and Bronchial Tree

Structures: trachea branches into right and left primary bronchi, further branching into secondary bronchi, tertiary bronchi, and bronchioles.

Tissues: cartilaginous rings; lined with mucous-secreting pseudostrati-fied ciliated columnar epithelium. Serves as a conducting system for air. Cartilaginous rings hold passages open.

Respiratory Division

Structures: continued branching into terminal bronchioles, alveolar ducts, alveolar sacs, pulmonary alveoli.

Tissues: Simple cuboidal epithelium in alveolar ducts, simple squamous epithelium in pulmonary alveoli.

Gas exchange occurs in the pulmonary alveoli, external respiration. Septal cells, which secrete a surfactant that lower the surface tension, and alveolar macrophages that remove foreign debris from the alveolus are found in the alveolar walls.


The paired lungs are contained within the thoracic cavity, separated from each other by the mediastinum (Figure 18-1). Each lung is com posed of lobes, and these, in turn, of lobules that contain the alveoli. The left lung has a cardiac notch on its medial surface. It is subdivided into two lobes by a single fissure and contains eight bronchial segments. The right lung is subdivided into three lobes by two fissures, and contains ten bronchial segments.

The lungs are surrounded by a two-layered serous membrane, the pleurae. The inner layer, visceral pleura, is attached to the surface of the lungs; the outer layer, parietal pleura, lines the thoracic cavity. Between the visceral and parietal pleura is a moist potential space, the pleural cavity. Air pressure in the pleural cavity (intrathoracic pressure) is slightly lower than atmospheric pressure in resting lungs. This negative pressure is critical for the thoracic cavity to "pull out" on the lungs causing them to inflate.

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