Như đã thấy từ chương đã nói ở trên, các sinh vật sống bị ảnh hưởng của một số lượng lớn các chất độc môi trường ngoài các chất dinh dưỡng thiết yếu được hấp thu. Chương này xem xét làm thế nào các sinh vật có thể có thể để đối phó với tác động của nhiều người trong số những chất độc. Hậu quả có thể xảy ra khi cơ chế phòng vệ như vậy không cũng sẽ được thảo luận. . | Chapter 7 Defense Responses to Toxicants INTRODUCTION As seen from the foregoing chapters living organisms are subjected to the influence of a large number of environmental toxicants in addition to the essential nutrients that are absorbed. This chapter examines how organisms may be able to respond to the impact of many of those toxicants. The consequences that may result when such defense mechanisms fail will also be discussed. RESPONSES OF HUMANS AND ANIMALS This section focuses on five body systems including the respiratory tract gastrointestinal tract membranes liver and kidneys in humans and in some instances in animals. THE Respiratory Tract An adult breathes more than 13 000 liters of air a day. This is not only the body s largest intake of any substance but also the most immediately important to life. Humans can go without food for many days and without water for many hours without serious health effects but life without air terminates in a very few minutes. Air is inhaled through the nasal cavity nasopharynx and trachea. The trachea divides into the main bronchi which go to the right and left lungs Figure . The right lung consists of three lobes and the left lung two. The bronchi divide into finer and finer tubes called bronchioles. Located at the ends of the bronchioles are many tiny air sacs called alveoli these are where the exchange of gases takes place. At the alveoli a thin sheet of moving blood picks up molecular oxygen O2 from the inhaled air and unloads carbon dioxide CO2 for exhalation. The respiratory tract is one of the principal ports of entry for air pollutants and is remarkably well equipped to cope with harmful invaders. There are three main processes that operate in their defense against the invasion of foreign agents filtration inactivation and removal. 2005 by CRC Press LLC Figure Generalized structure of human lungs a the tracheobronchial area with microscopic view showing a section of the ciliated epithelium that
