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Functions of the Respiratory System
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The respiratory zone begins with the respiratory bronchioles (generations 17–19), the first airways to have alveoli in their walls, through the alveolar ducts (generations 20–22) to the alveolar sacs (generation 23). The respiratory zone comprises the majority of lung volume, being 3000 mL in volume, and exchange of oxygen and carbon dioxide with pulmonary capillary blood occurs here, not by bulk flow but by diffusion of gas that takes place rapidly within the pulmonary lobule because of the very short distances involved.
The respiratory system
Published in C. Simon Herrington, Muir's Textbook of Pathology, 2020
The respiratory zone of the lung begins at the respiratory bronchiole and continues into alveolar ducts and alveoli. The alveolus is cup shaped and thin walled. Up to 96% of the alveolar wall is covered by type I pneumocytes, with thin cytoplasm to facilitate gas transfer between the alveolus and the pulmonary capillary. These cells are bound by tight junctions, which restrict the movement of ions and water. Approximately 7% of the alveolar surface is covered by type II pneumocytes, which lie in the corners of the alveolar walls. These cells form surfactant, phospholipids that lower the surface tension in the alveoli, thus preventing their collapse. These cells are also capable of cell division and are commonly hyperplastic following alveolar damage.
Physiology of the Airways
Published in Anthony J. Hickey, Sandro R.P. da Rocha, Pharmaceutical Inhalation Aerosol Technology, 2019
Anthony J. Hickey, David C. Thompson
The various levels of the airways may be categorized functionally as being either conducting or respiratory airways. Those airways not participating in gas exchange constitute the conducting zone of the airways and extend from the trachea to the terminal bronchioles. This region is the principal site of airway obstruction in obstructive lung diseases, such as asthma. The respiratory zone includes airways involved with gas exchange and comprises respiratory bronchioles, alveolar ducts, and alveolar sacs. As such, conducting and respiratory zones of the airways may be distinguished simply by the absence or presence of alveolar pockets (which confer gas exchange function). Regions within each zone may be classified further on a histological basis. For example, the contribution of cartilage to the airway wall is one means of differentiating the trachea from bronchi and bronchioles because cartilage exists as incomplete rings in the trachea, regresses to irregularly shaped plates in bronchi, and is absent from bronchioles. Also, respiratory bronchioles may be discriminated from terminal bronchioles by the presence of associated alveoli.
Sevoflurane Well-Handled in Children Is Excellent, but in the Wrong Hands Can Be Life-Threatening
Published in Journal of Investigative Surgery, 2021
From the reading of this study [10], another consideration which emerges in the working environment, is the risk of contamination of health personnel resulted from the use of sevoflurane. The authors describe that the halogenated agent is administered by inhalation through a nasal cannula, with high fresh gas flows, in an area where it may not be properly ventilated and where gas extraction systems may not exist. Gas extraction systems collect expired gases and evacuate them passively or actively outside the surgical room. An adequate ventilation system with renewal and treatment of the ambient air is the first link in the fight against pollution and reduces by 50% the environmental concentrations of anesthetic gases in the respiratory zone of the exposed personnel. Ventilation must conserve air sterility in the operative field and should maintain a comfortable environment for the occupants of the operating room [4, 5].
Targeting pulmonary tuberculosis using nanocarrier-based dry powder inhalation: current status and futuristic need
Published in Journal of Drug Targeting, 2019
Tulshidas S. Patil, Ashwini S. Deshpande, Shirish Deshpande, Pravin Shende
For the development of a targeted nanocarrier dosage form, the first step is to understand the respiratory system and second to select the desired target for drug delivery system. Briefly, the respiratory system can be divided into conducting and respiratory zones as shown in Figure 3 [17]. The conducting zone starts with nasal cavity followed by nasopharynx, the trachea, the bronchi and ends with terminal bronchioles. The respiratory zone starts with 17th bifurcation called respiratory bronchioles, which sub-divided into alveolar ducts and finally into alveolar sacs. From the trachea to alveoli, there are 23 bifurcations exist which in turn generate 23 airways. There are about 300 million alveoli in the human lungs with a surface area between 70 and 160 m2. Approximately 96% of the surface area of alveolar epithelium consists of pneumocytes type I and a small percentage of pneumocytes type II [17]. Alveolar epithelium is covered by airway lining layer which is composed of highly surface active pulmonary surfactant and its aqueous subphase [18]. AMs, the primary site of infection of M Tb bacilli, present in this aqueous subphase [17,19].
Computational modeling of lung deposition of inhaled particles in chronic obstructive pulmonary disease (COPD) patients: identification of gaps in knowledge and data
Published in Critical Reviews in Toxicology, 2019
Koustav Ganguly, Ulrika Carlander, Estella DG Garessus, Markus Fridén, Ulf G Eriksson, Ulrika Tehler, Gunnar Johanson
Lungs are composed of about half a liter of tissue, similar volume of blood and ∼4.3 liters (l) of air in a healthy “standard” man (30 y, 1.75 m, 70 kg) consisting of the trachea, two main bronchi, bronchioles, alveolar ducts and alveolar sacs. (Murray 2010). The classical Weibel’s model (Weibel 1963) described 23 generations of branching airways in the human respiratory tract that is classified into two zones: (a) Conducting zone (generations 0–16) and (b) Respiratory zone (generations 17–23) (ICRP 1994). The Conducting zone (100–150 ml) comprises of the trachea, bronchi, bronchioles and terminal bronchioles and delivers air to the respiratory zone (West 2007; Wang et al. 2014). It has a thick airway wall and is devoid of any alveoli, thereby not participating in the process of gas exchange (Weibel 1963). The respiratory zone (2.5–3 l) comprises of the respiratory bronchioles, alveolar ducts and alveolar sacs and facilitates the process of gas exchange at the blood-air barrier. Alveolar ducts and alveolar sacs are covered by alveoli, the gas exchange units of the lung (alveolar surface area: 70–80 m2) (Weibel 1963; West 2007; Wang et al. 2014). Mucociliary clearance is the process of mucus transport towards the throat by the coordinated ciliary beating (20 mm/min in trachea to 1 mm/min in small peripheral airways) and expiratory airflow to clear foreign objects out of the lung (West 1992; Wang et al. 2014). This process is an essential mechanism to clear respirable particulate matter from the respiratory tract. On the other hand, macrophagic phagocytosis is the main particle clearance mechanism within alveoli. Adult human lung consists of about 500 million alveoli with about 12–14 resident macrophages in each alveoli. Resident alveolar macrophages contribute to approximately 1% of the total alveolar surface area (Patton and Byron 2007; Geiser 2010; Geiser and Kreyling 2010; Wang et al. 2014). Particles that are small enough to penetrate into the alveolar tissue may also be cleared via translocation to lung-associated lymph nodes as shown in several animal species including humans (Snipes et al. 1983; Kitamura et al. 2007; Choi et al. 2010; Nakane 2012). The translocation appear to be small (<0.1% of the deposited dose) but can increase due to disease and inflammation in the lung (Nakane 2012; Keller et al. 2014; Bevan et al. 2018). Translocation of various types of fine and ultrafine particles have also been detected in the mediastinal and/or hilar lymph nodes in mice and rats, following inhalation, intra-nasal and/or intra-tracheal instillation (Shwe et al. 2005; van Ravenzwaay et al 2009; Pauluhn 2012; Nakane 2012). Another clearance mechanism, of importance particularly for soluble particles and small nanoparticles, is absorption into the systemic circulation (Kermanizadeh et al. 2015).