26.12.2014 Views

Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Chapter 20<br />

Thyroid Function<br />

J. Jerry Kaneko<br />

Department <strong>of</strong> Pathology, Microbiology, and Immunology<br />

School <strong>of</strong> Veterinary Medicine<br />

University <strong>of</strong> California, Davis<br />

Davis, California<br />

I. INTRODUCTION<br />

II. ANATOMICAL CONSIDERATIONS<br />

III. NUTRITIONAL REQUIREMENTS<br />

IV. IODINE METABOLISM<br />

V. FUNCTIONS OF THE THYROID GLAND<br />

A. Thyroid Hormones<br />

B. Hormonogenesis and Release<br />

VI. TRANSPORT OF HORMONE: PROTEIN BINDING<br />

VII. MECHANISM OF THYROID HORMONE ACTION<br />

A. General Effects <strong>of</strong> Thyroid Hormones<br />

B. Molecular Basis <strong>of</strong> Thyroid Hormone Action<br />

VIII. CATABOLISM AND EXCRETION OF THYROID<br />

HORMONES<br />

IX. REGULATION OF THE THYROID GLAND<br />

A. Production and Regulation <strong>of</strong> Thyroid-Stimulating<br />

Hormone<br />

B. Action <strong>of</strong> the Thyroid-Stimulating Hormone on the<br />

Thyroid Gland<br />

C. Action <strong>of</strong> the Thyroid-Stimulating Hormone on<br />

Hormonogenesis<br />

D. Long-Acting Thyroid Stimulators<br />

X. THYROID FUNCTION TESTS<br />

A. Indirect Tests <strong>of</strong> Thyroid Function<br />

B. Direct Tests <strong>of</strong> Thyroid Function<br />

C. Radionuclide Uptake Tests<br />

D. Thyroid Ultrasonography<br />

E. Trophic Hormone Response Tests<br />

XI. DISEASES OF THE THYROID<br />

A. Goiter<br />

B. Hypothyroidism<br />

C. Hyperthyroidism<br />

D. Tumors <strong>of</strong> the Thyroid Gland<br />

REFERENCES<br />

I . INTRODUCTION<br />

Disorders <strong>of</strong> the thyroid gland are the most common endocrine<br />

disorders in humans, and extensive historical and scientific<br />

literature is available. Among the domestic animals,<br />

thyroid function and its diseases are well known in companion<br />

animals but less so in other animals, domestic or<br />

wild. In livestock, nutritional iodine deficiencies have been<br />

<strong>of</strong> greater importance than thyroid gland diseases, particularly<br />

in the iodine-deficient areas <strong>of</strong> the world. The importance<br />

<strong>of</strong> thyroid function and its diseases has also become<br />

progressively more important as the longevity <strong>of</strong> companion<br />

animals such as the dog and the cat has increased.<br />

Advances in thyroid physiology, pathogenesis <strong>of</strong> its<br />

diseases, and the continued development and refinement<br />

<strong>of</strong> methods <strong>of</strong> testing thyroid function have added impetus<br />

to the study <strong>of</strong> thyroid disease in all animals. This chapter<br />

reviews the anatomy and physiology <strong>of</strong> the thyroid gland<br />

and its diseases as a corollary to the understanding <strong>of</strong> the<br />

pathophysiology <strong>of</strong> the thyroid gland in disease. Emphasis<br />

is placed on the physiological bases <strong>of</strong> a variety <strong>of</strong> thyroid<br />

function tests, most <strong>of</strong> which are now readily available to<br />

the veterinary clinician.<br />

II . ANATOMICAL CONSIDERATIONS<br />

The thyroid gland <strong>of</strong> animals is a bilobed structure that<br />

overlays the trachea at a point just below the larynx.<br />

Anatomical variations <strong>of</strong> the gland are marked between<br />

species and, to some extent, within a given species. The<br />

isthmus connecting the two lobes <strong>of</strong> the thyroid is the<br />

region that varies most markedly between species. Humans<br />

and pig have a large discrete isthmus, which forms a pyramidal<br />

lobe connecting the two lateral lobes. The cow has<br />

<strong>Clinical</strong> <strong>Biochemistry</strong> <strong>of</strong> <strong>Domestic</strong> <strong>Animals</strong>, 6th <strong>Edition</strong> 623<br />

Copyright © 2008, Elsevier Inc.<br />

All rights reserved.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!