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Unformatted text preview: second messenger to appear in the cytoplasm. Thyroid and steroid hormones cross the cell membrane and bind to receptors in the cytoplasm or nucleus. The hormone-receptor complex activates or inactivates specific genes. • Endocrine reflexes are the functional counterparts of neural reflexes. • The hypothalamus regulates the activities of the nervous and endocrine systems by three mechanisms: (1) It secretes regulatory hormones , which control the activities of endocrine cells in the pituitary gland; (2) its autonomic centers exert direct neural control over the endocrine cells of the adrenal medullae; and (3) it acts as an endocrine organ by releasing hormones into the bloodstream at the posterior pituitary. http://media.pearsoncmg.com/bc/bc_campbell_biology_6/medialib/assets/interactivemedia/activities/C6eActivityServer.ht ml?45&04&D:%20Human%20Endocrine%20Glands%20and%20Hormones...
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