Endocrinology review - adrenal and thyroid disorders.

1. Linda S. Gorman, PhD, MLS (ASCP)CM[⇑][1] 1. University of Kentucky, Lexington, KY 2. Janelle M. Chiasera, PhD, MT (ASCP) 1. University of Alabama at Birmingham, Birmingham, Alabama 1. Address for Correspondence: Linda S. Gorman, PhD, MLS (ASCP)CM , CLS Education Co-ordinator, Associate Professor, 900 S. Limestone Ave, Rm 126G CTW, University of Kentucky, Lexington, KY 40536-0200, (859)-218-0855, lsgorm0{at}uky.edu 1. Define endocrinology and list the major endocrine glands of the body. 2. Explain how feedback (positive and negative) promotes maintenance of normal levels of hormones. 3. Differentiate between steroid and peptide hormones with regard to their mechanism of action. 4. Provide examples of peptide and steroid hormones. 5. Explain how endocrine disorders are categorized. This article represents the first of three articles focusing on the endocrine system. The first article will provide you with fundamental theory regarding the endocrine system that will serve as a basis for understanding the next two articles focusing on two specific endocrine glands, the thyroid and adrenal glands. Endocrinology is the branch of medical science that deals with the endocrine system, a system that consists of several glands located in different parts of the body that secrete hormones directly into the bloodstream. Although every organ system in the body may respond to hormones, endocrinology focuses specifically on endocrine glands whose primary function is hormone secretion. Major endocrine glands include the pituitary (anterior and posterior), hypothalamus, thyroid, parathyroid, pineal, pancreas, adrenal (cortex and medulla), and gonads (ovaries and testes). Figure 1 shows the various locations of endocrine glands. The HPT Axis The endocrine system is part of the body's extracellular communication system that links the brain to various parts of the body and acts to control body metabolism, growth and development, and reproduction. The production and circulating levels of hormones are controlled by means of a feedback process that links the hypothalamus to the pituitary and the pituitary to a target gland. This linkage is referred to as the hypothalamus, pituitary, target gland (HPT) axis.1,2 Refer to Figure 2. In general terms, hormones are produced by specialized glands in one part of the body and travel through the bloodstream to result in a biological effect at a distant site. The… ABBREVIATIONS: ACTH - adrenocorticotropic hormone; ADH - antidiuretic hormone; CRH – corticotropin releasing hormone; DHEA – dehydroepiandrosterone; FSH - follicle stimulating hormone; GHRH - growth hormone releasing hormone; GnRH – gonadotropin releasing hormone; HPT - hypothalamus, pituitary, target gland; LH - luteinizing hormone; MBST - membrane-bound signal transducer; SRE - steroid response element; TRH - thyrotropin releasing hormone; TSH - thyroid stimulating hormone 1. Define endocrinology and list the major endocrine glands of the body. 2. Explain how feedback (positive and negative) promotes maintenance of normal levels of hormones. 3. Differentiate between steroid and peptide hormones with regard to their mechanism of action. 4. Provide examples of peptide and steroid hormones. 5. Explain how endocrine disorders are categorized. [1]: #corresp-1