The endocrine system produces hormones, a structurally diverse group of chemical messengers that regulate and coordinate whole body metabolism, growth, reproduction, and responses to external stimuli. The hypothalamic-anterior pituitary axis controls the synthesis and action of several major hormones: thyroid hormone, glucocorticoids, sex steroids, growth hormone, and prolactin. The hypothalamic-posterior pituitary axis controls the production and release of oxytocin and AVP/ADH. The action of these hormones on cells is controlled by receptors located either on cell membranes or intracellularly. Feedback mechanisms are important in controlling the endocrine systems. Both over-activity and under-activity of a hormone produce distinct clinical syndromes. Laboratory diagnosis of endocrine disorders relies heavily on the measurements of hormones in blood and also on function tests that check the integrity of endocrine regulatory systems.
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| The human body contains several other endocrine systems not considered in this chapter. Some of these are considered in other chapters as part of the physiologic function that they control. Thus the reader is referred to Chapter 20 for carbohydrate homeostasis, Chapter 24 for calcium homeostasis and Chapter 22 for water and electrolyte homeostasis and the control of blood pressure. The intracellular signaling systems through which hormones exert their effects are described in the next chapter.
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- Trace the flow of information from the hypothalamus to the ovum early in the menstrual cycle.
- How do GH, cortisol, and insulin interact to regulate lipid and carbohydrate metabolism?
- Because dietary iodide can vary greatly, thyroid hormones need to be synthesized and stored when iodide is available; but thyroid hormones are hydrophobic and cannot be contained within membrane vesicles. How does the thyroid gland solve this problem?
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Merza Z. Modern treatment of acromegaly. Postgrad Med J 2003;79:189-194.
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| Monzavi R, Cohen P. IGFs and IGFBPs: role in health and disease. Best Pract Res Clin Endocrinol Metab 2002;16:433-447.
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| Yen PM. Physiological and molecular basis of thyroid hormone action. Physiol Rev 2001;81:1097-1142.
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| Endotext: www.endotext.org
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| Cushing's Syndrome: www.medstudents.com.br/endoc/endoc7.htm
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| www.cushings-help.com/HPAaxis.htm
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| Thyroid hormone: www.thyroidmanager.org
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| Glucocorticoids: www.uspharmacist.com/NewLook/CE/glucocort/lesson.htm
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