Chapter 2 Thyroid Hormone Synthesis and Secretion

نویسندگان

  • Françoise Miot
  • Corinne Dupuy
  • Jacques E Dumont
  • Bernard A. Rousset
چکیده

The main function of the thyroid gland is to make hormones, T4 and T3, which are essential for the regulation of metabolic processes throughout the body. As at any factory, effective production depends on three key components adequate raw material, efficient machinery, and appropriate controls. Iodine is the critical raw material, because 65% of T4 weight is iodine. Ingested iodine is absorbed and carried in the circulation as iodide. The thyroid actively concentrates the iodide across the basolateral plasma membrane of thyrocytes by the sodium/iodide symporter, NIS. Intracellular iodide is then transported in the lumen of thyroid follicles. Meanwhile, the thyrocyte endoplasmic reticulum synthesizes two key proteins, TPO and Tg. Tg is a 660kDa glycoprotein secreted into the lumen of follicles, whose tyrosyls serve as substrate for iodination and hormone formation. TPO sits at the apical plasma membrane, where it reduces H2O2, elevating the oxidation state of iodide to an iodinating species, and attaches the iodine to tyrosyls in Tg. H2O2 is generated at the apex of the thyrocyte by Duox, a NADPH oxydase. Initial iodination of Tg produces MIT and DIT. Further iodination couples two residues of DIT, both still in peptide linkage, to produce T4, principally at residues 5 in the Tg polypeptide chain. When thyroid hormone is needed, Tg is internalized at the apical pole of thyrocytes, conveyed to endosomes and lysosomes and digested by proteases, particularly the endopeptidases cathepsins B, L, D and exopeptidases. After Tg digestion, T4 and T3 are released into the circulation. Nonhormonal iodine, about 70% of Tg iodine, is retrieved intrathyroidally by DEHAL1, an iodotyrosine deiodinase and made available for recycling within the gland. TSH is the stimulator that affects virtually every stage of thyroid hormone synthesis

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

The Regulation of Thyroid-stimulatinghormone Synthesis and Secretion: Molecular Biology and Biochemistry

The activity of the thyroid gland is predominantly regulated by the concentration of the pituitary glycoprotein hormone, thyroid-stimulating hormone (TSH). In the absence of pituitary or of thyrotroph function hypothyroidism ensues. Thus, regulation of thyroid function in normal individuals is to a large extent determined by the factors which regulate the synthesis and secretion of TSH. Those f...

متن کامل

Thyrotoxicosis of other Etiologies

Thyrotoxicosis is defined as the clinical syndrome of hypermetabolism resulting from increased free thyroxine (T4) and/or free triiodothyronine (T3) serum levels (1). The term thyrotoxicosis is not synonymous with hyperthyroidism, the elevation in thyroid hormone levels caused by an increase in their biosynthesis and secretion by the thyroid gland (Table 1) (2). For example, thyrotoxicosis can ...

متن کامل

Growth and Development in a incidentally diagnosed Resistance to Thyroid Hormone

Resistance to thyroid hormone is an uncommon condition. We report the clinical and laboratory findings of a case with both resistance to thyroid hormone and, a reduced capacity to produce and respond to thyroid hormone. RTH is a disorder characterized by elevated circulating thyroid hormones, state of non-suppressed pituitary TSH secretion and refractoriness to hormone action in peripheral tiss...

متن کامل

Physiology of the Hypothalamic-Pituitary Thyroidal System

The activity of the thyroid gland is predominantly regulated by the concentration of the pituitary glycoprotein hormone, thyroid stimulating hormone (TSH). In the absence of pituitary or of thyrotroph function hypothyroidism ensues. Thus, regulation of thyroid function in normal individuals is to a large extent determined by the factors which regulate the synthesis and secretion of TSH. Those f...

متن کامل

Seasonal change of thyroid histomorphological structure and hormone production in yellowfin seabream (Acanthopagrus latus) in the Persian Gulf

 Seasonal changes of the thyroid gland structure and hormones secretion was examined in yellowfin seabream (Acanthopagrus latus) in the northwest of Persian Gulf (Musa creek). Thyroid gland composed of follicles scattered around the ventral aorta, near the gills. Follicular cells varied according to secretion of the gland during warm and cold seasons. Thyroid hormones (Triidothyronine [T3] and ...

متن کامل

Effect of Aerobic Exercise on Thyroid Hormones and Quality of Life in Obese Postmenopausal Women

ABSTRACT            Background and objectives: Studies have shown that exercise can affect hormone secretion and some metabolic and endocrine functions. The aim of this study was to assess the effect of eight weeks of aerobic training on thyroid hormones and quality of life in obese postmenopausal women.            Methods: In this semi-experimental study, 21 obese (body mass index >30 Kg/m2)...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 2015