Terminal bronchiole, diameter

Inhaled particles of 20 [im diameter or more tend to be retained in upper parts of the respiratory tract (trachea, pulmonary bronchi and terminal bronchioles) and then removed by ciliary action. In contrast, smaller particles of around 6 pm diameter reach all parts of the respiratory system including the alveolar sacs. Smaller (2 pm) and very small particles (0.2 pm) may not reach the alveolar sacs, only the terminal bronchioles and alveolar ducts. Particles of diameter 1 pm or less may be absorbed if they reach the alveolar sacs. 

As a powder, e.g. sodium cromoglicate. Particle size and air flow velocity are important. Most particles above 5 micrometres in diameter impact in the upper respiratory areas particles of about 2 micrometres reach the terminal bronchioles a large proportion of particles less than micrometer will be exhaled. Air flow velocity diminishes considerably as the bronchi progressively divide, promoting drug deposition peripherally. 

Pulmonary deposition of an aerosol preparation is determined primarily by its size. Aerosols with a mass median aerodynamic diameter of 1-5 xm produce the best therapeutic results and are the target particle size for inhalation therapy. These small particles penetrate deep within the respiratory tract to ensure drug deposition in peripheral airways. The cross-sectional area (cm ) of the lung increases dramatically at the level of the respiratory zone therefore, the velocity of gas flow during inspiration rapidly decreases at this level. Moderate-sized particles (5-10 (xm) frequently settle out by sedimentation in larger more central airways because the velocity of gas falls rapidly in the region of the terminal bronchioles. 

Tracheo-bronchial (TB) region. This begins at the larynx and comprises the trachea, bronchi and bronchioles. The branching airways are smaller and more numerous at each division, ending with the terminal bronchioles which are about 0.5 mm in diameter. 

The hazards presented by toxins dispersed by an atypical aerosol route include stability and the ability to remain in an aerosol (particles greater than 15-20 microns fall out of the aerosol). The retention of particles within the terminal bronchioles and alveoli of the lung is also a factor. They achieve entry in this way (particles must be less than two microns in diameter). 

Inhalation is the most important route of exposure to fibers. Only some fibers can be inhaled and deposited in the respiratory tract. The respirability of fibers is largely determined by two variables density and cross-sectional area length plays only a minor role in determining respirability. Fibers with aerodynamic equivalent diameters between 5 and 10 pm can deposit in the larger airways, and those less than 5 pm can reach the terminal bronchioles and alveoli. This latter aerodynamie diameter is equivalent to a fiber diameter of approximately 3 pm however, density will also affect this value. 

Fig. 3.1 Schematic diagram of the human respiratory system. The gross anatomy of the lung, the covering membranes (pleura), airways and air sacs (alveoli) are shown. The average diameter of portions of the air flow system are indicated trachea, 20 mm bronchus, 8 mm terminal and respiratory bronchioles, 0.5 mnn alveolar duct, 0.2 mm alveolar sacs, 0.3 mm.

At ambient temperatures, H. capsulatum grows as a mold. The mycelial phase consists of septate branching hyphae with terminal micro- and macroconidia that range in size from 2 to 14 microns in diameter. When soil is disturbed, these conidia become aerosolized and reach the bronchioles or alveoli. ... 

The earliest histological feature is proliferation of Langerhans cells found around terminal and respiratory bronchioles (3,21). These early cellular lesions expand to form nodules that are typically 1 to 6 mm in diameter (21). These bronchiolo-centric nodules characteristically have a stellate configuration (Fig. la). The morphology of the nodules varies with the activity of the lesions. Early lesions are cellular. The peribronchiolar interstitium and adjacent alveolar septa are thickened by clusters of Langerhans cells admixed with variable numbers of eosinophils, neutrophils, lymphocytes, macrophages, and fibroblasts. Eosinophils are often numerous and can form eosinophilic abscesses but may be absent in up to 20% of... 

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