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The principles of toxicology environmental and industrial applications 2nd edition phần 4

Các tính năng khác của hành vi động hóa chất hoặc phương thức quản lý có thể được đưa vào mô hình cho phù hợp. Ví dụ, có thể có nhiều hơn một mô ngoại vi, như trong Hình 2.1, hoặc hấp thụ, mà là không bao giờ thực sự tức thời ngay cả đối với tiêm tĩnh mạch, có thể được đặt hàng đầu tiên thay vì. Tiếp xúc bằng miệng, trong đó tốc độ hấp thu thường | 9.1 LUNG ANATOMY AND PHYSIOLOGY 173 Figure 9.4 Photomicrograph of lung tissue showing the relationship of a terminal bronchiole TB and its accompanying blood vessel the pulmonary artery PA to the alveoli. Reproduced with permission from J. F. Murray The Normal Lung. The Basis for Diagnosis and Treatment of Pulmonary Disease Saunders Philadelphia 1976. to the alveolus and the alveolar epithelium. In many instances the red blood cells are just barely able to fit through the small capillaries so the blood cell wall is often in very close proximity to this membrane complex with the alveolus. Figure 9.5 illustrates how the remarkable design discussed above facilitates gas exchange. Carbon dioxide and oxygen readily cross this membrane complex in a process of simple dìlĨLision.Many inhaled airborne industrial chemicals will also readily cross this membrane and will enter the bloodstream. These potential toxins thus enter the blood circulatory system in a manner analogous to someone receiving an intravenous infusion of a drug. A unique view of the alveoli is provided in Figure 9.6. The small holes called pores of Kohn provide for some ventilation between adjacent alveoli. Toxicologic insult to the lung as well as various disease states can result in a functional derangement of this membrane system. Exposure to some chemicals may result in an increase in fluid in the interstitial space. If sufficient fluid accumulates a condition known as pulmonary edema gas exchange can be hindered sufficiently to result in severe difficulty in breathing and even in death. Damage to the membrane itself can result in scarring which may increase the thickness of the membrane or decrease the elasticity of the lung tissue or both. As with pulmonary edema an increase in the thickness of the membrane can deleteriously affect pulmonary gas exchange. Alterations in elasticity make the work of breathing harder which can decrease the volume of respiration as the individual tires from the increased