Many cells of mammals, including man, depend on hormones for the expression of their full activities. Hormones are chemical messengers elaborated by a specific cell found usually in one organ, but sometimes in more than one. Hormones vary in their chemical structure, site and regulation of secretion, and mode of action.
KeywordsThyroid Hormone Endocrine Gland Exocrine Gland Polypeptide Hormone Acetoacetic Acid
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