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special senses, Hormones and receptors

special senses, Hormones and receptors - second messenger...

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H o r m o n e s a n d R e c e p t o r s Summary: In general, the nervous system performs short-term "crisis management," whereas the endocrine system regulates longer-term, ongoing metabolic processes. Endocrine cells release chemicals called hormones , which alter the metabolic activities of many tissues and organs simultaneously. Hormones exert their effects by modifying the activities of target cells . Hormones can be divided into three groups on the basis of chemical structure: amino acid derivatives , structurally similar to amino acids; peptide hormones , chains of amino acids; and lipid derivatives , including steroid hormones and eicosanoids . Hormones may circulate freely or bound to transport proteins. Free hormones are rapidly removed from the bloodstream. Receptors for catecholamines and peptide hormones are located on the cell membranes of target cells; the hormone acts as a first messenger , which causes a
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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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special senses, Hormones and receptors - second messenger...

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