Respiratory System Primary Cells

Figure 1. Components of the respiratory system [6].

2.Lower respiratory tract: The lower respiratory tract consists of the trachea, the primary bronchi and the lungs. Thetrachea and the bronchi in the lower respiratory tract conduct air between the upper respiratory tract and the lungs. Each bronchus branches into secondary bronchi, and so on. These passages form an inverted tree-like shape with repeated branching as moving deeper into the lungs (Figure 1). The lungs consist mainly of alveoli, which are the functional units of the lungs where gas exchange takes place. It is only in the lungs that gas exchange occurs between the air and the bloodstream [7, 8].

3.Besides these organs, certain muscles of the thorax are also involved inrespiration by enabling breathing. The most important one is the large muscle called the diaphragm, locating below the lungs and separating the thorax from the abdomen [9]. Contraction of the diaphragm increases the volume of the thoracic cavity, allowing air to be drawn into the lungs; relaxation of the diaphragm decreases the volume of the thoracic cavity, causing air to be expelled from the lungs.

Primary cell types of the respiratory system

The cells of the respiratory system cooperate to facilitate gas exchange, a vital life process taking place in alveoli, by transporting oxygen between the alveoli and the capillary network that surrounds them and delivering it to the body’s tissues, while simultaneously expelling carbon dioxide.

Primary cells of the respiratory system typically refer to cells isolated and purified from a wide variety of donors without the accumulated mutations found in immortal cell lines. Respiratory research benefits from these primary cells as they represent more physiological or pathological conditions. Here are some common types of primary cells in the respiratory system:

1.The respiratory epithelial cells: From the nasal cavity through the bronchi to the lung, therespiratory tract is covered in the epithelium. The airway epithelial cells play a unique role to external deleterious agents as a protective physical and functional barrier. Many diseases of the airway involve damage to the airway surface epithelium.

The bronchial epithelium is made up of the surface epithelial cells and mucus glands. The surface epithelial cells consist of three principle cell types: basal, goblet, and ciliated cells. These epithelial cells are crucial for studying infection, inflammation, and other diseases of the respiratory system.

Alveolar epithelial cells cover more than 99% of the internal surface of the lung and are also valuable cell models for study.

2.The vascular endothelial cells: These endothelial cellscontribute to the vascular homeostasis maintenance. They synthesize and secrete activators, inhibitors of both the fibrinolysis system and the coagulation system, and mediators which influence the blood platelets adhesion and aggregation. They also release molecules that can control cell proliferation and modulate vessel wall tone. The pulmonary microvascular endothelial cells function as a semiselective barrier that is critical for gas exchange and regulation of fluid and solute passage between the blood and interstitial compartments in the lungs.

3.Airway smooth muscle cells: Airway smooth muscle exists in the trachea and in the bronchial tree up to the terminal bronchioles. Their regulatory mechanisms and specialized features are the basis for normal airway function. In severe asthma patients, the characteristic feature is the increase in bronchial smooth muscle mass. Airway smooth muscle cells are also valuable models for studying diseases like bronchospasm, chronic bronchitis, and emphysema [10].

4.Fibroblasts: Fibroblasts,the most abundant cell type in lung interstitium, are one of the easiest types of cells to grow in culture. Pulmonary fibroblasts play an important role in the repair and remodeling processes following injury.

5.Pulmonarymacrophages: Pulmonary macrophages are widely distributed in the lung interstitium. They are active in phagocytosis, immunity and secretion and have important defence functions. Macrophages isolated from pulmonary interstitial tissues are essential components of the immune system responsible for clearing foreign particles and pathogens [11][12][13][14].

6.Epithelial stem cells: Stem cells present in the airway and lung epithelium, possessing the potential for self-renewal and differentiation into various epithelial cells [15][16].

Conclusion

The primary cells derived from the respiratory system are invaluable tools for numerous research applications. The utilization of them would significantly advance current research in uncovering the underlying mechanisms of various respiratory disorders and viral infections, offering critical insights into potential therapeutic avenues.