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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).
Comparative Aspects of Pulmonary Surfactant
Published in Jacques R. Bourbon, Pulmonary Surfactant: Biochemical, Functional, Regulatory, and Clinical Concepts, 2019
The lung of Aves — possibly the most performing gas-exchanging organ in animals in relation to the high metabolic rate of birds and/or the rapid changes in oxygen pressure with changes in altitude during flight — is built on a completely different pattern. Contrary to the blind-ending structure of the mammalian lung, it presents as an open-ending structure inserted between the major conducting airways and the air sacs, which are pouches extending into the thorax and abdomen. This remarkable design allows air renewal in lungs at both inspiration and expiration, allowing air circulation through the lungs, in contrast to the alternate inflow and outflow which occur in the mammalian lung. The airways present three orders of bronchi. The complicated system of primary and secondary bronchi serves as connecting channels to the air sac as well as to the tertiary bronchi (parabronchi) which carry air to the exchanging areas. These are formed of air capillaries whose segmentation achieves the enlargement of surface area required in these highly active species.
Fetal Circulation
Published in Miriam Katz, Israel Meizner, Vaclav Insler, Fetal Well-Being, 2019
Miriam Katz, Israel Meizner, Vaclav Insler
At the same time, when lung buds grow into the primitive pleural cavity, the primary bronchi subdivide into secondary bronchi, which undergo subsequent dichotomous branchings. The segmental (tertiary) bronchi begin to form by week 7 of gestation. Concurrently, the surrounding mesenchymal tissue divides, so that the tertiary bronchi with its mesenchyme will form a bronchopulmonary segment.23
Simulation of respiratory tract lining fluid for in vitro dissolution study
Published in Expert Opinion on Drug Delivery, 2021
Rakesh Bastola, Paul M. Young, Shyamal C. Das
The respiratory system consists of mouth and nose, pharynx, larynx, trachea, bronchi, bronchioles and alveoli [9]. The pharynx is approximately 12–15 cm in length and it is divided into nasopharynx, oropharynx and laryngopharynx [10]. The larynx works as a sphincter and transmits air from oropharynx and nasopharynx to the trachea [11]. The trachea is divided into the left and right primary bronchi. Each bronchus is divided into secondary bronchi, which are further divided into many tertiary bronchi. Branching of tertiary bronchi gives many tiny bronchioles which finally, lead to terminal and respiratory bronchioles. Respiratory bronchioles are further divided into alveolar ducts which end at the alveoli (alveolar sacs) [11]. There are more than 300 million alveoli in the lungs. Each alveolus is lined with pulmonary capillaries, which forms a massive network that includes more than 280 billion capillaries with a surface area of around 70 m2 [12].
Endobronchial high-intensity ultrasound for thermal therapy of pulmonary malignancies: simulations with patient-specific lung models
Published in International Journal of Hyperthermia, 2019
Dong Liu, Matthew S. Adams, Chris J. Diederich
Models A and B were used to investigate distinct prospective cases, including targeting of tumors attached or adjacent to major bronchi (major airways) and tumors adjacent to small diameter tertiary bronchi (deep lung). Different applicator configurations, tumor sizes and distances from the bronchial wall were incorporated as summarized in Table 2. Specifically, bronchial wall thickness was set at 1.5 mm at major bronchi and 0.75 mm at tertiary bronchi, and lumen diameters were set as 10 mm at major airways and 2.5–5 mm at smaller airways, based on measurements extracted from multi-detector CT imaging [58]. Tumor sizes in terms of radial depth extent were set as 1–3 cm at major airways and 0.5–1.5 cm at smaller airways with normal air-filled lung parenchyma (Model A, Figure 3(a)), and 2 cm at major airways and 1 cm at smaller airways with saline flooding lung parenchyma (Model B, Figure 3(b)). Acoustic power deposition profiles were calculated using Equations (S1)–(S6) in Supplemental materials, and imported into COMSOL Multiphysics 5.3 (COMSOL Inc., Burlington, MA) for thermal simulations. In the models described in Table 2, the absorption coefficient for all tissues is assumed to be equal to the corresponding attenuation coefficient, with all scattered energy locally absorbed. Some studies have suggested that the absorption coefficient (59–61]. As such, additional parametric studies using the geometry of Model A were performed to investigate the influence of lower absorption coefficient in lung tissue, as described in section 2 of the supplemental materials. Acoustic surface intensities of the transducers were iteratively adjusted to achieve a maximum temperature of 75 °C within a 5 min sonication time. The resulting temperature profiles central to the transducer surface were analyzed to evaluate the performance of the endobronchial applicators. The minimum and maximum penetration depths were defined as the proximal and distal depths of the 52 °C temperature contour from the inner bronchial wall, corresponding to approximately 240 EM43°C thermal dose margins. The ablative margin was defined as the distance that the 52 °C temperature contour exceeded the target tumor boundary in the depth direction.