Page 656 - Atlas of Histology with Functional Correlations

CHAPTER 17 Respiratory System

COMPONENTS OF RESPIRATORY

SYSTEM

The respiratory system is made up of two parts, a conducting portion and a
respiratory portion. Also located in the air passages of the nose are

neuroepithelial sensory cells that detect odor or smell.

The conducting portion consists of passageways or tubes located outside
(extrapulmonary) and inside (intrapulmonary) of the lungs that conduct air for
gaseous exchange to and from the lungs. In contrast, the respiratory portion

consists of passageways within the lungs that not only conduct the air but also
allow respiration or gaseous exchange.

Such extrapulmonary passages as the trachea and different sizes of bronchi
are lined with a pseudostratified ciliated epithelium with numerous goblet
cells. As these bronchi enter the lungs, they undergo extensive branching, and

their diameters become progressively smaller. There is also a gradual decrease in
the height of the lining epithelium, the amount of cilia, and the number of goblet
cells. The bronchioles represent the terminal portion of the conducting
passageways. These give rise to the respiratory bronchioles, a transition zone

between air conduction and respiratory or gaseous exchange regions.

The respiratory portion consists of respiratory bronchioles, alveolar ducts,
alveolar sacs, and alveoli (Fig. 17.1). Gaseous exchange takes place in the
alveoli, the very thin terminal air spaces of the respiratory system. In the alveoli,
goblet cells are absent and the lining epithelium is thin simple squamous. The

alveoli are in very close proximity to the capillaries.

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