China
Africa
Explore chapters and articles related to this topic
Oxygen Transport
Published in James N. Cobley, Gareth W. Davison, Oxidative Eustress in Exercise Physiology, 2022
P.N. Chatzinikolaou, N.V. Margaritelis, A.N. Chatzinikolaou, V. Paschalis, A.A. Theodorou, I.S. Vrabas, A. Kyparos, M.G. Nikolaidis
At the first step of oxygen transport, the atmospheric air is channeled to the lungs through ventilation at the alveolar-capillary region, to replace oxygen and remove carbon dioxide (Figure 4.2). The gas exchange between the alveoli and pulmonary capillaries is facilitated via passive gas diffusion, from a high to low-pressure gradient. In human lungs, the number of alveoli is ≈4.8 × 108 (Ochs et al., 2004) and is estimated to occupy a large surface area of ≈60–80 m2 (Pittman, 2016). The alveoli are in close contact with the pulmonary capillaries, separated only by a thin air-blood barrier ≈0.2–0.6 μm thick (Hall, 2016). Each alveolus has a wide diameter of ≈200 μm (Ochs et al., 2004), whereas a pulmonary capillary could be as small as ≈3–5 μm (Hall, 2016; Pittman, 2016; Kuck, Peart and Simmonds, 2020). The erythrocytes are evidently larger cells (i.e., ≈7–8 μm diameter) than capillaries and have to change their shape and mechanical properties to traverse through the pulmonary capillaries and bind oxygen (Kuck, Peart and Simmonds, 2020) (Figure 4.3). Overall, the large surface area of the alveolar region, the thin air-blood barrier, the difference in gas pressure gradients and the erythrocyte’s ability to deform greatly enhance gas diffusion at this step.
Application of Stem Cell and Exosome-Based Therapy in COVID-19
Published in Debmalya Barh, Kenneth Lundstrom, COVID-19, 2022
Suleyman Gokhan Kara, Ayla Eker Sariboyaci
MSCs are being tested in lung damage caused by COVID-19 through their ability of endothelial and epithelial repair, bacterial and alveolar fluid clearance, and their anti-inflammatory and anti-apoptotic effects. COVID-19 pneumonia occurs because of damage to the alveoli. It is necessary to know alveolar histopathology to understand the mechanism of damage. The alveolar epithelium consists of Type I and Type II pneumocytes. Type I pneumocytes occupy 95% of the alveolar surface and are responsible for gas exchange, while Type II pneumocytes secrete surfactant, reduce alveolar surface tension, and protect from alveolar collapse. In COVID-19 pneumonia, Type II pneumocytes become infected by the virus, and cell death occurs. The decrease in surfactant causes alveolar collapse. The migration of inflammatory cells and mediators into the alveoli results in the development of alveolar oedema. As a result of these events, cell death also occurs in Type I pneumocytes. Lung alveolar epithelium has limited regeneration. Type I pneumocytes are unable to replicate. In the event of damage, Type II pneumocytes can proliferate and differentiate into Type I pneumocytes. The function of this repair mechanism changes according to the extent of the damage. When alveolar damage is mild, a repair mechanism preserves lung function. However, if there is extensive alveolar damage, fibrosis or emphysema develops, and the alveoli lose their function.
Mechanical Properties of the Lungs
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
In the lung, the effect of the fluid lining the alveoli is minimized by the production of surfactant, which acts as a detergent, reducing the force of attraction between water molecules and thus reducing surface tension. Type II alveolar cells produce surfactant and store it in the cytoplasmic lamellated bodies. The half-life of surfactant is 15–30 hours and most of its components are recycled by the type II cells.
Pinealectomy and melatonin administration in rats: their effects on pulmonary edema induced by α-naphthylthiourea
Published in Drug and Chemical Toxicology, 2023
Mohammed Raed Abdullah Al Gburi, Eyup Altinoz, Hulya Elbe, Melike Ozgul Onal, Umit Yilmaz, Nesibe Yilmaz, Melike Karayakali, Mehmet Demir
Pulmonary edema is a clinical disorder leading to respiratory failure (Barile 2020). The disorder is observed due to the hydrostatic effect of elevated pulmonary vascular pressure and blood volume. The Alveolar-capillary membrane is an extremely thin structure that allows optimal gas exchange and serves as a barrier to fluid accumulation in the alveolar space, limiting the diffusion of solute volumes physiologically (Comellas and Briva 2009). There is a significant balance between alveolar fluid uptake and secretion in the maintenance of optimal gas exchange in the alveolar space. The alveolar-capillary membrane’s increased permeability allows the passage of fluid and protein into the interstitial fluid space and alveoli (Casey et al. 2019). Excessive accumulation of pleural fluid was described as pleural effusion (PE), which leads to a common problem induced by several mechanisms and disorders (Allibone 2006). Several lung diseases could be associated with PE. PE plays a key role in the respiratory system, especially the normal changes associated with age that compromise the respiratory system (Wing 2004). In particular, it reduces pulmonary gas exchange while leading to restriction of lung functions based on the fluid volume and the reduction in lung compliance (Ruiz et al. 2006).
Mathematical analysis of oxygen and carbon dioxide exchange in the human capillary and tissue system
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Ahsan Ul Haq Lone, M. A. Khanday
The human respiratory system has two main functions: oxygen intake from the surrounding air to the body, and to exhale carbon dioxide from the blood to outside air. Those transfers are achieved through passive diffusion across a membrane which separates the gaseous air and the liquid blood, at an instantaneous rate by means of the difference in partial pressures, the area of the exchange surface, and its properties in terms of diffusion (Guyton and Hall 2011; West 2011). As this diffusion tends to reduce the partial pressure difference, a constant renewal must be made on both sides of the membrane. Renewal of air is achieved by the ventilation process, which consists of in periodic inspiration-expiration cycles that provide the inside of the lung with fresh air, whereas venous blood is periodically pumped onto the exchange zone by the heart. The exchange area is the boundary of a huge collection of small cavities (around 300 million units), called alveoli, which makes an exchange area of about 100 m2 (Guyton and Hall 2011; West 2011; Tortora and Derrickson 2012; Nunn 2013). Each of this alveolus is surrounded by a network of very small blood vessels, called capillaries, whose diameter is about 5–10 μm (Guyton and Hall 2011; West 2011). Gas exchange occur through the alveolar-capillary membrane, which is less than a micrometre wide (West 2011; Tortora and Derrickson 2012). The alveoli are connected to the outside world through the respiratory tract, which is an assembling of interconnected pipes following a dyadic-tree structure.
Effect of first order chemical reactions through tissue-blood interface on the partial pressure distribution of inhaled gas
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
We observed that the present state in the above studies have the following limitations - (i) the models do not permit flow through tissue-blood interface i.e. inter capillary flow, which can be helpful to predict the effect of concurrent capillary and capillary transit-time heterogeneity (ii) the models do not consider tissue porosity, therefore incapable to simulate the effect of aging and various lung diseases which affect partial pressure of a gas. Therefore, in this study, we analyzed the effect of porosity of alveolar tissue due to aging and various lung disease together-with flow through an interface and its simultaneous effect on partial pressure distribution and dispersion coefficient. It is assumed between the alveolar tissue and pulmonary capillary there is a thin liquid layer also known as pericilliary layer through which gas may go through a linear first-order chemical reaction within the bloodstream and on the boundary. We discussed how the variations in the tissue porosity, inter capillary oxygen gradients, radial mixing affect the short time and short distance dispersion with the combined effects of kinetic reversible phase exchange and irreversible absorption affects the partial pressure of inhaled gas inside a respiratory system by using a method of moments. A comparative study is also done with previously published result by Saini et al. (2010).