Bronchioles respiratory

Alveolar duct Airway distal to respiratory bronchiole leading to individual alveoli and alveolar sacs. 

Branching from the terminal bronchioles are the respiratory bronchioles. This is the first generation of airways to have alveoli in their walls. Finally, there are the alveolar ducts which are completely lined with alveolar sacs. This region, from the respiratory bronchioles through the alveoli, is referred to as the respiratory zone, which comprises most of the lungs and has a volume of about 3000 ml at the end of a normal expiration. 

Parenchymal changes affect the gas-exchanging units of the lungs (alveoli and pulmonary capillaries). Smoking-related disease most commonly results in centrilobular emphysema that primarily affects respiratory bronchioles. Panlobular emphysema is seen in AAT deficiency and extends to the alveolar ducts and sacs. 

Respiratory effects are more likely to occur after inhalation exposure to high concentrations of chloroform. It has been demonstrated that chloroform has a destructive influence on the pulmonary surfactant (Enhoming et al. 1986). This effect is probably due to the solubility of phospholipids in the surfactant monolayer and can cause collapse of the respiratory bronchiole due to the sudden increase in inhalation tension. Immediate death after chloroform inhalation may be due principally to this effect in the lungs (Fagan et al. 1977). It is unlikely that exposure levels of chloroform in the general environment or at hazardous waste sites would be high enough to cause these severe respiratory effects. 

The sites of action and effects of ozone and other photochemical oxidants are described in Chapters 8 and 9. Recent work with primates has suggested that ozone is absorbed along the entire respiratory tract, penetrates more into the peripheral nonciliated airways, and causes more lesions in the respiratory bronchioles and alveolar ducts as the inhaled ozone concentration increases from 0.2 to 0.8 ppm. The most common and most severe tissue damage was observed in the respiratory bronchioles. The ciliated cells in the terminal bronchioles and the Type 1 cells in the epithelial layer of the proximal alveoli of rats were the... 

Continuous for up to 3 weeks Morphologic changes in distal and respiratory bronchioles, alveolar ducts, and associated alveoli Young rat 72... 

Continuous for 18 months Thickening of terminal and respiratory bronchioles barely noticeable at 1 ppm at 3 ppm. formation of peribronchiolar collars with resulting narrowing of small airways Dog 73... 

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.

XB = tracheobronchial (trachea, bronchi, bronchioles to terminal bronchioles) pu = pulmonary (respiratory bronchioles, alveolar region)... 

Conducting Bronchiole Terminal Bronchiole Respiratory Bronchiole Alveolar Duct... 

The transition zone consists of the respiratory bronchioles (generations 17 to 19), which contain alveoli. At the terminal end, the respiratory zone is composed of parenchyma that contains the alveolar ducts and about 300 million alveoli (alveolar sacs) to provide the gas-exchange surface. Since the surface area expands to such a large extent within the very last generations of bifurcations, the inhalation airflow rapidly slows down to zero velocity so that the movement of gas molecules and the exchange occurs entirely by diffusion (Stocks and Hisloop 2002). 

The pharynx, larynx, trachea and bronchi are lined with pseudostratified, ciliated columnar epithelium that contain at least eight cell types, including mucous secretory goblet and Clara cells, which produce a protective mucus layer of 5-10 jum thickness (see Table 9.2). Subepithelial secretory glands, present in the bronchial submucosa, also contribute to the mucus blanket [9]. Through coordinated ciliary movement a propulsive wave is created, which continuously moves the mucus layer up towards the larynx. Consequently, the mucosal surface of trachea and bronchi is constantly swept to remove inhaled materials. As the bronchi divide into bronchioli, the ciliated columnar respiratory epithelium is much thinner and changes to a simpler non-ciliated cuboidal epithelium. The epithelium in the terminal and respiratory bronchioles consists of ciliated, cuboidal cells and a small number of Clara cells. However, Clara cells become the most predominant type in the most distal part of the respiratory bronchioles [10]. 

Functional smooth muscle by 8-10 weeks, to respiratory bronchioles by 26 weeks... 

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