Unit 5 the impact of chemical elements on human organism

Exercise 12. 9 a). Name the main principles of toxicokinetics. Characterise each of them.

b). You will hear the description of the process taking place at each stage of toxicokinetics. Decide which description corresponds to what principle.

Tapescript

1. These system transforms the xenobiotic in a series of steps from the original compound to a series of stable compounds, often through intermediate unstable compounds. For xenobiotics there are many pathways of this process. An active xenobiotics may be transformed into an inactive compound, which effectively removes the agent from the body in its toxically active form. However, an inactive precursor may also be transformed into active agent.

2. Kidney is the major rout of this process for most xenobiotics. Those that are water soluble or eliminated unchanged. The reserve capacity of the kidney is very great and this mechanism is rarely saturated in healthy people. Xenobiotics that are themselves nephrotoxic may injure the kidney and reduce their own clearance thereby enhancing their own toxicity by further accumulation.

3. The skin is sufficiently permeable to be a major route of this process for many chemicals, particularly those that are readily lipid-soluble. It is highly variable, depending on skin characteristics and solubility of xenobiotics in fat. Most processes occur directly across the superficial layers of the skin. When the skin is injured with open wounds or in the presence of a skin rash, it takes place much faster.

4. When a xenobiotics is dissolved in plasma, some fraction of the total usually binds to circulating proteins, particularly albumin (which binds many organic compounds as well as calcium, copper, and zinc). Metals may also be bound to specialized proteins in the plasma. As the concentration of free xenobiotics falls in plasma, some molecules will separate from their binding sites until a new equilibrium is reached.

Exercise 13. a). Name the organs involved in each stage of toxicokinetics.

Absorption may occur through lungs, mouth, skin, sometimes blood.

Distribution takes place through heart, capillary, blood.

Metabolism takes place in ventricle (stomach), liver, and pancreas.

Excretion occurs in kidneys, bowels (кишечник), lungs (expired air), gall bladder (желчный пузырь).

References

1. Dara S.S. A Textbook of Environmental Chemistry and Pollution Control. Delhi, 2001.

2. Lower S. K. Survey of Environmental Geobiochemistry. Simon Fraser University, 2004.

3. Mascull B. Key Words in Science and Technology. The University of Birmingham, 1997.

4. Положинцев Б. И. Introduction to ecology. СПб.: Химера, 1999.

5. General engineering.

6. Evans V., Dooley J. Enterprise 4. Express publishing, 1998.

7. E. A. Keller, D.B. Botkin. Essential Environmental Science. John Wieley & Sons, Inc., 2007.

8. Essentials of Medical Geology. Elsevier Inc., 2005.

9. Rye D., Greenall S. CAE: Listening and Speaking Skills, 2004.

10. Fowler W.S. New Fowler proficiency. Listening and speaking, 2003.

11. Johnson C.N. & D. General Engineering. Prentice Hall, Europe, 1998.