Respiratory system bronchioles

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.

By this mechanism they can block reflex laryngospasm during surgery. In addition, these drugs are potent inhibitors of secretions throughout the respiratory system, from the nose to the bronchioles. 

FIGURE 10.1 Schematic representation of the lower respiratory system. The trachea leads into the bronchioles that branch and finally reach the alveolar sacs only on one side of the bronchial tree. Inset represents the alveolar tubules and alveolar sacs present at the terminal portions of the bronchial tree. 

Figure 3.10 The structure of the mammalian respiratory system (A) trachea, (B) bronchiole, (C) alveolar sac with blood supply, (D) arrangement of blood vessels around alveoli, (E) arrangement of cells and airspaces in alveoli showing the large surface area available for absorption, (F) cellular structure of alveolus showing the close association between (G) the endothelial cell of the capillary (H) with erythrocytes and (I) the epithelial cell of the alveolar sac. The luminal side of the epithelial cell is bathed in fluid, which also facilitates absorption and gaseous exchange. Source From Ref. 1.

Volatile irritants such as ammonia and chlorine initially cause constriction of the bronchioles. These two gases are water soluble, are absorbed in the aqueous secretions of the upper airways of the respiratory system, and may not cause permanent damage. Irritant damage may however lead to changes in permeability and edema, the accumulation of fluid. Some irritants such as arsenic compounds cause bronchitis. 

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. 

Similarly, no respiratory effects were found in rats and mice chronically exposed by diet to 5/ 10" and 1.3 10s g/kg/day of 2,7-DCDD, respectively (NCI/NTP 1979a). In contrast, rats exposed chronically by gavage to a mixture of 1,2,3,6,7,8-HxCDD and 1,2,3,7,8,9-HxCDD at 0.18, 0.34, and 0.7 g/kg/day had a dose-related increased incidence of adenomatous hyperplastic lesions in terminal bronchioles and adjacent alveoli of both males and females no such effects were found in mice exposed chronically to 0.7 g/kg/day of that same mixture (NCI/NTP 1980). The existing information suggests that in animals, the respiratory system is not a sensitive target for CDDs toxicity via oral exposure. 

Respiratory toxicity Upper respiratory system (nose, pharynx, larynx, and trachea) and the lower respiratory system (bronchi, bronchioles, and lung alveoli) Pulmonary irritation Asthma/bronchitis Emphysema Allergic alveolitis Fibrotic lung disease Lung cancer... 

Respiratory bronchiole Microscopic channel in the lower respiratory system that ends in a series of alveoli. 

Inhalation During respiration, airborne gases and particulates move into the upper respiratory system and lungs. Figure 24-1 illustrates the structure of the respiratory system. Air passes through the pharynx and trachea to the bronchi, bronchioles, and ultimately to the terminal air sacks or alveoli. 

The three-stage glass impinger developed by May is intended to correspond with the three deposition sites of the human respiratory system (Figure 13.5). The top stage corresponds to the upper respiratory tract, the middle stage to the bronchioles and the bottom stage to the alveoli. The... 

Respiratory history As noted above, formaldehyde has recognized properties as an airway irritant and has been reported by some authors as a cause of occupational asthma. In addition, formaldehyde has been associated with cancer of the entire respiratory system of humans. For these reasons, it is appropriate to include a comprehensive review of the respiratory system in the medical history. Components of this history might include questions regarding dyspnea on exertion, shortness of breath, chronic airway complaints, hyperreactive airway disease, rhinitis, bronchitis, bronchiolitis, asthma, emphysema, respiratory allergic reaction, or other preexisting pulmonary disease. 

The ICRP deposition model estimates the fraction of inhaled material initially retained in each compartment (see Figure 3-2). The model was developed with five compartments (1) the anterior nasal passages (ET,) (2) all other extrathoracic airways (ET2) (posterior nasal passages, the naso- and oropharynx, and the larynx) (3) the bronchi (BB) (4) the bronchioles (bb) and (5) the alveolar interstitium (AI). Particles deposited in each of the regions may be removed and redistributed either upward into the respiratory tree or to the lymphatic system and blood by different particle removal mechanisms. 

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