Alveolar blood vessels

Exposure (concentrations and concentration fluctuations in the ambient air, exposure time, physical exertion). The alveolar concentration of solvents or the difference between air and blood concentration levels determine the diffusion process into alveolar blood vessels. Physical exertion influences lung parameters, especially ventilation, and consequently alveolar and blood concentrations. 

Two different circulatory systems, the bronchial and the pulmonary, supply the lungs with blood [133], The bronchial circulation is a part of the systemic circulation and is under high pressure. It receives about 1% of the cardiac output and supplies the conducting airways, pulmonary blood vessels and lymph nodes [133], It is important for the distribution of systemically administered drugs to the airways and to the absorption of inhaled drugs from the airways [18]. The pulmonary circulation comprises an extensive low-pressure vascular bed, which receives the entire cardiac output. It perfuses the alveolar capillaries to secure efficient gas exchange and supplies nutrients to the alveolar walls. Anastomoses between bronchial and pulmonary arterial circulations have been found in the walls of medium-sized bronchi and bronchioles [18, 65, 67],... 

Fig. 3.6 Sketch of an alveolar-capillary unit showing alveolar spaces, cells, and a blood vessel. AM — alveolar macrophage, PMN = polymorphic nucleosite. Other cells indicated Type I and II intraalveolus, a fibroblast in the interstitium, and endothelial cells lining the adjacent capillary. ChTV = chemotaxin.

Figure 3.10 The structure of the mammalian respiratory system (A) trachea, (B) bronchiole, (C) alveolar sac with blood supply, (D) arrangement of blood vessels around alveoli, (E) arrangement of cells and airspaces in alveoli showing the large surface area available for absorption, (F) cellular structure of alveolus showing the close association between (G) the endothelial cell of the capillary (H) with erythrocytes and (I) the epithelial cell of the alveolar sac. The luminal side of the epithelial cell is bathed in fluid, which also facilitates absorption and gaseous exchange. Source From Ref. 1.

A heroin addicted patient, who had been foUowed up for 6 months for increasing dyspnea due to chronic cor pulmonale, was admitted to an intensive care unit. She died shortly after. Postmortem lung biopsies showed talc particles within alveolar walls and alveolar macrophages, as well as alterations in blood vessels (26). 

In the guinea pig TRPV1-positive nerve fibers are locahzed within the epithelium of the trachea and around smooth muscle and blood vessels and within the lower airways, in the vicinity of bronchi and bronchioles, and around alveolar tissue, whereas no TRPV 1 was found within airway epithelial cells (Watanabe et al. 2005). The physiological relevance of TRPVl mRNA expression, together with that of other ion channels in bronchial epithehal cells (Agopyan et al. 2003), remains questionable. Similarly, expression of TRPV 1 in dendritic cells (Basu and Srivastava, 2005) and the associated hypothesis that TRPV 1 orchestrates an early immune response has been challenged by failure to detect any functional TRPV 1 in these inflammatory cells (O Connell et al. 2005). We cannot exclude that in the airways, as in other tissues, TRPV 1 occurs in extraneuronal cells, from where it may contribute to homeostasis, inflammation, and ultimately the regulation of the tussive response. However, we underline that this hypothesis lacks conclusive experimental proof. 

There is no true pulmonary analogue to the systemic arterioles, since the pulmonary circulation occurs under relatively low pressure [West, 1977]. Pulmonary blood vessels, especially capiQaries and venules, are very thin walled and flexible. Unlike systemic capillaries, pulmonary capillaries increase in diameter, and pulmonary capillaries within alveolar walls separate adjacent alveoli with increases in blood pressure or decreases in alveolar pressure. Flow, therefore, is significantly influenced by elastic deformation. Although pulmonary circulation is largely unaffected by neural and chemical control, it does respond promptly to hypoxia. 

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