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Chapter-31 Endocrinology

BOOK TITLE: Textbook of Biochemistry for Dental Students

Author
1. Vasudevan DM
2. S Sreekumari
3. Vaidyanathan Kannan
ISBN
9789350254882
DOI
10.5005/jp/books/11333_31
Edition
2/e
Publishing Year
2011
Pages
12
Author Affiliations
1. Faculty of Medicine, Amrita Vishwa Vidyapeetham, (Amrita University), Kochi, Kerala, Formerly Principal, College of Medicine, Amrita, Kerala; Formerly, Dean, Sikkim Manipal Institute of Medical Sciences, Gangtok, Sikkim, Amrita Vishwa Vidyapeetham (Deemed University), Cochin, Kerala, E-mail: dmvasudevan@aims.amrita.edu, PG Programs and Research College of Medicine, Amrita Institute of Medical Sciences, Kochi, Kerala, India, College of Medicine, Amrita Institute of Medical Sciences, Kochi, Kerala, India; Sikkim Manipal Institute of Medical Sciences, Gangtok, Sikkim, India
2. Jubilee Mission Medical College, Trissur, Kerala, Sree Gokulam Medical College and Research Foundation, Thiruvananthapuram, Kerala, India, Jubilee Mission Medical College and Research Institute, Thrissur, Kerala, India, Government Medical College, Thrissur and Thiruvananthapuram, Kerala, India; Sree Gokulam Medical College and Research Foundation, Thiruvananthapuram, Kerala, India; Jubilee Mission Medical College and Research Institute, Thrissur, Kerala, India
3. Amrita Institute of Medical Sciences, Kochi, Kerala, India, Pushpagiri Institute of Medical Sciences and Research Centre, Thiruvalla, Kerala, India, Believers Church Medical College and Hospital, Thiruvalla, Kerala, India
Chapter keywords

Abstract

G protein is a peripheral membrane protein consisting of alpha, beta and gamma subunits. When GTP is attached, it becomes active. It then activates the enzyme adenylate cyclase. G proteins are used for different signal transduction pathways. There are 2 major types of G proteins; GS (G stimulatory) and GI (G inhibitory). G protein activity can be inhibited by GTPase. Examples of hormones that use cyclic AMP as second messenger are ACTH, FSH, LH. PTH, etc. Examples of hormones that use calcium or PIP2 as second messenger are TRH, GnRH, CCK, etc. Examples of hormones whose actions are mediated via a tyrosine kinase mechanism are Insulin, EGF, PDGF NGF, etc. Diacylglycerol (DAG), the second messenger formed by the hydrolysis of PIP2 activates protein kinase C which in turn phosphorylates other target proteins. Hormones bind to the specific area of the gene, referred to as the hormone response element (HRE), e.g. thyroid hormones and steroid hormones. The adrenal cortex has three different zones each responsible for production of different classes of steroid hormones (C21, C19 and C18). Zona glomerulosa produces the C21 steroids, mineralocorticoids. Zona fascicularis produces the glucocorticoids mainly; and adrenal androgens and estrogens to a lesser extent. Zona reticularis produces the androgens (C19) and estrogens (C18). Cortisol in blood is bound to cortisol binding globulin (CBG) or transcortin. Hyperactivity of adrenal cortex may be due to primary defect in adrenal gland itself (Cushing’s syndrome) or secondarily by excessive production of ACTH from pituitary (Cushing’s disease) or ectopic ACTH production by other malignant tumors. Congenital deficiency of steroid hydroxylases leading to deficient secretion of cortisol is the cause for Adrenogenital syndrome. The main hormones secreted by the thyroid gland are tri-iodo thyronine (T3) and tetra-iodo thyronine or thyroxine (T4). Measurement of T4 and T3 levels in blood are done by ELISA. Cholesterol is increased in blood in hypothyroidism. Grave’s disease and Hashimoto’s thyroiditis are produced by auto-immune mechanisms. Most common cause of hypothyroidism is primary thyroid disease, often auto-immune in nature, leading to myxedema in adults. Women are more affected than males. In children, hypothyroidism produces mental and physical retardation, known as cretinism. Euthyroid goiter can result from iodine deficiency. Insulin has the following biochemical effects: increases uptake of glucose by cells, enhances utilization of glucose, hypoglycemic, antilipolytic, antiketogenic and favors lipogenesis. Insulin acts via a specific insulin receptor present on cells of insulin responsive tissues. This affects a signal transduction pathway, which leads to regulation of gene transcription, DNA synthesis and activation of enzymes.

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