Lead

Physiological Role
Absorption and Metabolism
Sources of Pb
Poisoning Symptoms

I.  A physiological role for Pb has not been identified and it is generally not considered to be essential for animals

II.  Absorption and Metabolism

1. Amount of Pb absorbed depends on exposure route
   1. Intestinal absorption of Pb is relatively low (< 2% in sheep)
   2. Retention of inhaled Pb is much higher (37% in humans)
2. Homeostatic control appears to be lacking for Pb
3. Pb initially concentrates in bone until a possible threshold is reached
4. Pb is then deposited in other tissues, especially the kidney
5. Mobilization of Pb from bone keeps Pb in blood above normal long after exposure

III.  Sources of Pb

1. Soil and water contamination
   1. Waste from metal smelters
   2. Formerly combustion of leaded gasoline and use of lead arsenate pesticides
   3. Sewage sludge
2. Lead based paint
3. Used motor oil, discarded batteries, etc.

IV.  Poisoning Symptoms

1. Symptoms of Pb poisoning appear when Pb is distributed throughout the body, especially in the kidney, liver, and central nervous system
2. Clinical signs
   1. Central nervous system
      1. Depression
      2. Irritability
      3. Peripheral neurophathy
      4. Encephalopathy
      5. Blindness
      6. Laryngeal paralysis
      7. Convulsive seizures
   2. Digestive tract
      1. Constipation, diarrhea, abdominal pain
      2. Vomiting, increased salivation
      3. Esophageal paralysis
3. Pathological effects
   1. Derangement of porphyrin and heme synthesis
   2. Mechanical fragility of red blood cell membranes
   3. Interference in protein and globin synthesis
   4. Enzyme changes (either inhibited or enhanced activity)
   5. Altered endocrine function
   6. Young fail to grow
   7. Bones and nervous system fail to develop
   8. Skin becomes dry and thickened
   9. Kidneys mad various glands degenerate
   10. Both males and females become sterile

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