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Molecular Pathophysiology and the Clinical Presentation of COVID-19
Published in Srijan Goswami, Chiranjeeb Dey, COVID-19 and SARS-CoV-2, 2022
Srijan Goswami, Ushmita Gupta Bakshi
The trachea separates into two primary (main) bronchi called right and left bronchi. Inside the lungs, each primary bronchus separates into secondary bronchi which are further subdivided into tertiary bronchi. These tertiary bronchi form bronchioles. Bronchioles having a diameter of 1 mm or less are known as terminal bronchioles. The trachea and bronchi are together called the tracheobronchial tree. The structural and functional unit of lungs, known as the respiratory unit, consists of respiratory bronchioles, alveolar ducts, alveolar sacs, antrum, and alveoli, and is responsible for the actual exchange of gases between lungs and blood. Each alveolus is lined by epithelial cells called alveolar cells or pneumocytes. Pneumocytes are of two types (Hall, 2015; Ralston et al., 2018):Type I alveolar cells. Type I alveolar cells are the squamous epithelial cells forming about 95% of the total number of cells. These cells form the site of gaseous exchange between the alveolus and blood (Hall, 2015; Ralston et al., 2018).Type II alveolar cells. Type II alveolar cells are cuboidal in nature and form about 5% of alveolar cells. These cells are also called granular pneumocytes. Alveolar fluid and surfactant are secreted by these cells (Hall, 2015; Ralston et al., 2018) (Figure 3.5).
Ageing
Published in Henry J. Woodford, Essential Geriatrics, 2022
In older adults, there is a reduction in lung elastic recoil (making them stretchier) but also a reduction in chest wall compliance (making expansion less easy). Associated with frailty, muscles of respiration (including the diaphragm) become less strong. The combined effect of these changes is that total lung capacity (TLC) remains constant, but the reduced elastic recoil results in an increase in residual volume (RV). Vital capacity (VC) can be calculated by subtracting RV from TLC. Therefore, VC becomes reduced (seeFigure 1.4). Forced expiratory volume in one second (FEV1) is lower in older adults. As is diffusing capacity. Loss of terminal bronchioles contributes to age-related decline in pulmonary function.58 Partial pressure of oxygen (pO2) is reduced but that of carbon dioxide (pCO2) is unchanged. Respiratory drive in response to hypoxia or hypercapnia is impaired.
Battlefield Chemical Inhalation Injury
Published in Jacob Loke, Pathophysiology and Treatment of Inhalation Injuries, 2020
Phosgene is primarily toxic in the more peripheral airways. This is presumably due in part to the relatively low rate of hydrolysis, which limits its absorption in the upper airways. It may also be in part due to the physiological effect of an eightfold volume dilution of gas entering the alveolar ducts from the terminal bronchioles. Such dilution delays local clearance of inhaled gases/ fumes and promotes local toxicity (Gross et al., 1967).
Nanocrystals based pulmonary inhalation delivery system: advance and challenge
Published in Drug Delivery, 2022
Pengfei Yue, Weicheng Zhou, Guiting Huang, Fangfang Lei, Yingchong Chen, Zhilin Ma, Liru Chen, Ming Yang
The lungs are the organs that contact with the exchange of air between the organism and the outside world. They are divided into two main regions: the conducting airway region and the respiratory region. The airway is a continuous branch from the bronchi to the lungs and consists mainly of bronchi, bronchioles, and terminal bronchioles. As the bronchi continue to branch, the diameter of the tubes becomes smaller, the tube wall becomes thinner, and the structure of the tube wall changes gradually. The annular smooth muscles of the bronchi contract or relax under splanchnic nerves innervation and it is responsible for the regulation of airflow passage into the alveoli. This is the site where the lung tissue completes gas exchange consisting of respiratory bronchioles, alveolar ducts, lung sacs, and alveoli. The respiratory bronchiole is the transitional pipes between the pulmonary airway and the respiratory site. Each respiratory bronchiole branch is divided into 2–3 alveolar ducts. The alveolar sacs are the common opening of several alveoli and are connected to the alveolar ducts. The gut is the main site for the digestion and absorption of nutrients.
Predictions of inter- and intra-lobar deposition patterns of inhaled particles in a five-lobe lung model
Published in Inhalation Toxicology, 2021
Renate Winkler-Heil, Majid Hussain, Werner Hofmann
The bronchial airway structure of the stochastic, asymmetric five-lobe lung model is based on the extensive morphometric measurements of Raabe et al. (1976), where airway dimensions and angles of the bronchial region were recorded for the trachea and all bronchial airways down to about airway generation 10, while only 10 − 25% of bronchiolar airways down to the terminal bronchioles were measured. To construct a complete stochastic asymmetric bronchial tree model, measured airway diameters, lengths, branching, and gravity angles were statistically analyzed in terms of frequency distributions and correlations among several parameters (Koblinger and Hofmann 1985). Since the location of each bronchial airway in the morphometric data is classified by a binary identification number, this data set is the only currently available morphometric data base which allows the construction of a stochastic lobar lung model. The morphometrically observed branching asymmetry and variability of airway dimensions lead to highly variable pathlengths from the trachea to the terminal bronchioles. For example the shortest path comprises 11 generations and the longest path 21 generations. As a result, intermediate airway generations are composed of bronchial and alveolated airways at variable degrees of superposition. For a detailed description of the stochastic bronchial airway model, the reader is referred to the original papers of Koblinger and Hofmann (1985, 1990).
Airborne particulate matter from goat farm increases acute allergic airway responses in mice
Published in Inhalation Toxicology, 2020
Dingyu Liu, James G. Wagner, Rob Mariman, Jack R. Harkema, Miriam E. Gerlofs-Nijland, Elena Pinelli, Gert Folkerts, Flemming R. Cassee, Rob J. Vandebriel
The BioPM-induced inflammatory response in the airway wall and peri-bronchiolar interstitial tissue (bronchiolitis) consisted of a mixed inflammatory cell influx of polymorphonuclear leukocytes (neutrophils) and lesser numbers of mononuclear leukocytes (mainly lymphocytes) and eosinophils (type 1 immunity/inflammation characteristic of a nonallergic toxic response). Large and small diameter bronchioles were affected as well as centriacinar regions including the terminal bronchioles and proximal alveolar ducts and associated alveoli. Associated with the airway inflammation in the large-diameter, but not small-diameter, bronchioles, was an occasional mucous cell metaplasia (secretory cells with AB/PAS-stained mucosubstances not normally found in bronchioles of mice) in the luminal airway epithelium. However, this epithelial change was of minimal severity.