the blood flow to thyroid gland os how many times the weight of gland per minute
Answers
Thyroid hormones are extremely important and have diverse actions. They act on virtually every cell in the body to alter gene transcription: under- or over-production of these hormones has potent effects. Disorders associated with altered thyroid hormone secretion are common and affect about 5% women and 0.5% men.
Like the catecholamines epinephrine and norepinephrine, thyroid hormones are synthesized from the amino acid tyrosine. The synthesis of thyroid hormones requires the iodination of tyrosine molecules and the combination of two iodinated tyrosine residues (Box 3.1). Whilst tyrosine is relatively easily iodinated, iodine is rare, ranking 61st in the list of most common elements and forming just 0.000006% of the Earth's mantle. The thyroid gland has evolved not only to trap this element avidly from dietary sources but also to maintain a large store of the iodinated tyrosines to maintain the secretion of thyroid hormones during periods of relative iodine deficiency. Clinical Case 3.1 illustrates the importance of iodine in thyroid function and, whilst it is relatively unusual, it demonstrates the problems of excess iodine intake and a consequent increase in thyroid hormone synthesis and release.