Interfere with or block the active sites of some important enzymes b. Which of the following refers to a substance that is attached to an antigen and promotes an antigenic response. IgA e. IgD 17. Lead has been recognized as a hazard since early civilization when it was used to store wine, to pipe water, and even as vessels in which to cook food. Once a potential toxic substance goes into our society, it automatically produces an adverse effect.
External respiration refers to the exchange of gases between blood and individual cells.
Sulfur oxides tend to reach deep into lung tissue while nitrogen dioxides tend to act in the upper moist airways of the respiratory tree. The skin is the body's largest organ and consistis of many interconnected tissues. Epidermis is the outer, thinner layer of the skin and dermis is the inner and much thicker layer of the skin. The gastrointestinal tract is a major route of absorption for many toxic agents including mercury, lead, and cadmium. A toxin can produce a harmful effect upon an organ only by stimulating the normal metabolic actions of that particular organ.