DSE OF THE THYROID
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Questions and Answers

Which of the following inhibits the iodination of tyrosine residues of thyroglobulin?

  • Exocytosis and proteolysis
  • Large intake of iodine (<150mcg/day)
  • Coupling of DIT and MIT
  • Thioamides (correct)

    • What is the result of the coupling of DIT and MIT?

  • DIT
  • MIT
  • T4
  • T3 (correct)

    • Where are T4 and T3 released from?

  • Thyroglobulin (correct)
  • Pituitary gland
  • Thyroid gland
  • Follicular cells

    • What is the result of the coupling of DIT and DIT?

    <p>T4</p> Signup and view all the answers

    Which of the following drains into the brachiocephalic vein?

    <p>Inferior thyroid vein</p> Signup and view all the answers

    What is the term for the conversion of T4 to T3 in peripheral tissue?

    <p>Deiodination</p> Signup and view all the answers

    In iodine-sufficient areas, what is the most common cause of hypothyroidism?

    <p>Chronic autoimmune (Hashimoto) thyroiditis</p> Signup and view all the answers

    What is the path of the left recurrent laryngeal nerve?

    <p>Posteriorly around the aortic arch to ascend through the superior mediastinum</p> Signup and view all the answers

    What is the effect of increased TSH levels on the thyroid gland?

    <p>Increased gland size and vascularity</p> Signup and view all the answers

    What is the most sensitive test for hypothyroidism?

    <p>TSH levels</p> Signup and view all the answers

    What is a common musculoskeletal symptom of hypothyroidism?

    <p>Arthralgia</p> Signup and view all the answers

    What is a common pulmonary symptom of hypothyroidism?

    <p>Dyspnea on exertion</p> Signup and view all the answers

    What is a common genitourinary symptom of hypothyroidism?

    <p>Menstrual irregularity</p> Signup and view all the answers

    What is characteristic of subclinical hypothyroidism?

    <p>Elevated TSH and normal free T4</p> Signup and view all the answers

    What percentage of thyroid hormone is synthesized by the thyroid gland?

    <p>90%</p> Signup and view all the answers

    What is the boundary of the thyroid gland anteriorly?

    <p>Carotid sheath</p> Signup and view all the answers

    What is the most common cause of hypothyroidism worldwide?

    <p>Iodine deficiency</p> Signup and view all the answers

    What is the function of thyroid peroxidase antibodies?

    <p>Catalyzing the oxidation of iodine</p> Signup and view all the answers

    What is the classification of hypothyroidism in order of decreasing frequency?

    <p>Thyroid, pituitary, hypothalamic failure</p> Signup and view all the answers

    What is the percentage of thyroid peroxidase antibodies elevated in thyroid disease?

    <p>11.3%</p> Signup and view all the answers

    What is the type of laryngeal nerve that is not active?

    <p>Superior laryngeal nerve</p> Signup and view all the answers

    What is the percentage of free thyroid hormone in the bloodstream?

    <p>0.04%</p> Signup and view all the answers

    What is the definition of overt thyrotoxicosis?

    <p>High serum T4 and T3 concentrations and low serum TSH concentrations</p> Signup and view all the answers

    What is the most common cause of thyrotoxicosis?

    <p>Grave's disease</p> Signup and view all the answers

    What is the term for a late manifestation of hypothyroidism characterized by coma or precoma?

    <p>Myxedema coma</p> Signup and view all the answers

    What is the characteristic of patients with subclinical thyrotoxicosis?

    <p>Normal serum T4 and T3 concentrations and low serum TSH concentrations</p> Signup and view all the answers

    What is the common complication of overtreatment with an excessive dose of T4 in postmenopausal women?

    <p>Bone loss</p> Signup and view all the answers

    What is the term for the pathophysiological mechanism underlying thyrotoxicosis?

    <p>Unregulated release of T4 and T3</p> Signup and view all the answers

    What is the characteristic of patients with myxedema coma?

    <p>Extreme hypothermia</p> Signup and view all the answers

    What is the percentage of patients with thyrotoxicosis who have Grave's disease?

    <p>60%-85%</p> Signup and view all the answers

    What is the term for the transient or persistent syndrome that results from exposure to excessive concentrations of thyroid hormones?

    <p>Thyrotoxicosis</p> Signup and view all the answers

    What is the characteristic of patients with overt thyrotoxicosis?

    <p>Most patients have symptoms and signs of this entity</p> Signup and view all the answers

    What is the typical characteristic of the increase in T3 and T4 production in patients with thyrotoxicosis?

    <p>The increase in T3 production is greater than the increase in T4 production</p> Signup and view all the answers

    Which of the following groups of people is most likely to have high serum T3 concentrations but normal serum T4 concentrations?

    <p>Some patients with thyrotoxicosis</p> Signup and view all the answers

    What is the most common cause of thyrotoxicosis?

    <p>Graves' disease</p> Signup and view all the answers

    In which of the following groups is Graves' disease most likely to occur?

    <p>Women 30 to 60 years old</p> Signup and view all the answers

    Which of the following hormones may stimulate the production of thyroid-stimulating hormones?

    <p>Chorionic gonadotropin</p> Signup and view all the answers

    In which of the following situations is it particularly difficult to maintain a euthyroid state?

    <p>In patients in whom it is difficult to render and maintain a euthyroid state</p> Signup and view all the answers

    Study Notes

    Thyroid Gland

    • Synthesizes 90% T4 and 9% T3
    • 0.04% free T4 and 0.4% free T3
    • Not active, with long t1/2

    Boundaries

    • Anteriorly: Carotid sheath
    • Laterally: SCM and Carotid sheath

    Laryngeal Nerve

    • Superior laryngeal nerve
    • External laryngeal nerve
    • Internal laryngeal nerve
    • Recurrent laryngeal nerve

    Venous Drainage

    • Superior Thyroid Vein from external jugular vein
    • Middle thyroid vein from external jugular vein
    • Inferior thyroid vein from brachiocephalic and subclavian vein

    Organification

    • Tyrosine residues of thyroglobulin are iodinated
    • Inhibited by large intake of iodine (>150mcg/day) and thioamides (hyperthyroidism therapy)
    • Produce monoiodotyrosine (MIT) and diiodotyrosine (DIT) residues

    Coupling

    • DIT + MIT = T3
    • DIT + DIT = T4

    Storage

    • Along with thyroglobulin

    Exocytosis and Proteolysis

    • Release of T4 and T3

    Conversion of T4 to T3 in Peripheral Tissue

    • T4 vs. T3

    Thyroid Function Test

    • Thyroid hormone (TH) production and secretion regulated by pituitary's TSH
    • Two thyroid hormones: T4 and T3
    • As TH decreases, TSH increases to stimulate thyroid gland
    • Increased TSH levels stimulate gland size and vascularity

    Laboratory

    • Most sensitive test for hypothyroidism is elevated serum TSH
    • In subclinical hypothyroidism, TSH is elevated, whereas free T4 remains normal

    Thyrotoxicosis

    • Clinicopathologic and biochemical syndrome resulting from excessive thyroid hormone concentrations
    • Can be overt or subclinical
    • Overt thyrotoxicosis: high serum T4 and T3 concentrations and low serum TSH concentrations
    • Subclinical thyrotoxicosis: normal serum T4 and T3 concentrations and low serum TSH concentrations

    Pathophysiology

    • Unregulated release of T4 and T3 from thyroid gland or ingestion of excessive amounts of T4 or T3
    • Can be due to increased T4 and T3 synthesis and release because of intrinsic thyroid disease, excessive TSH, or other thyroid-stimulating hormones

    When to Consult an Endocrinologist?

    • In children and infants
    • In patients in whom it is difficult to render and maintain a euthyroid state
    • During pregnancy
    • In women planning to conceive
    • In cardiac disease

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