Many steroid and thyroid hormones circulate in the blood bound to specific carrier proteins (e.g., Sex Hormone-Binding Globulin for androgens/estrogens, Thyroxine-Binding Globulin for thyroid hormones). Only the small 'free' fraction is biologically active and can enter cells. Some chemicals, like certain industrial pollutants (e.g., some PCBs) or pharmaceuticals, can compete with the natural hormone for binding sites on these carrier proteins. By displacing the hormone from its transport protein, the chemical increases the circulating concentration of the free, active hormone. This effectively amplifies the hormone's signal without the chemical itself acting on the receptor. This is a subtle but important indirect mechanism of endocrine disruption that can lead to symptoms of hormone excess (e.g., hyperthyroidism) even if the gland's production rate is normal.

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Zambia

• Joseph Soko – 101 pts

• Visual Pathway Lesions
• Positive and Negative Symptoms
• Hallucinations and Delusions
• Antipsychotic Medications
• Emergency: Environmental Emergencies