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 (A)</p> Signup and view all the answers

Which of the following drains into the brachiocephalic vein?

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

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

<p>Deiodination (C)</p> Signup and view all the answers

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

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

What is the most sensitive test for hypothyroidism?

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

What is a common musculoskeletal symptom of hypothyroidism?

<p>Arthralgia (A)</p> Signup and view all the answers

What is a common pulmonary symptom of hypothyroidism?

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

What is a common genitourinary symptom of hypothyroidism?

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

What is characteristic of subclinical hypothyroidism?

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

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

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

What is the boundary of the thyroid gland anteriorly?

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

What is the most common cause of hypothyroidism worldwide?

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

What is the function of thyroid peroxidase antibodies?

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

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

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

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

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

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

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

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

<p>0.04% (A)</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 (B)</p> Signup and view all the answers

What is the most common cause of thyrotoxicosis?

<p>Grave's disease (A)</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 (C)</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 (D)</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 (C)</p> Signup and view all the answers

What is the term for the pathophysiological mechanism underlying thyrotoxicosis?

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

What is the characteristic of patients with myxedema coma?

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

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

<p>60%-85% (A)</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 (C)</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 (D)</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 (C)</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 (C)</p> Signup and view all the answers

What is the most common cause of thyrotoxicosis?

<p>Graves' disease (B)</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 (C)</p> Signup and view all the answers

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

<p>Chorionic gonadotropin (A)</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 (B)</p> Signup and view all the answers

Flashcards

Thyroid Hormone Synthesis

Mainly synthesizes T4 (90%) and T3 (9%) but also contains free forms of each.

Thyroid Gland Boundaries

Carotid sheath anteriorly and SCM and Carotid sheath laterally.

Laryngeal Nerves

Superior, External, Internal and Recurrent.

Thyroid Venous Drainage

Superior and Middle drain into the internal jugular vein. Inferior drains into the brachiocephalic and subclavian vein.

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Organification in Thyroid Hormone Synthesis

Amino acid residues of thyroglobulin are iodinated. Inhibited by high iodine intake and thioamides. Creates MIT and DIT.

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Coupling in Thyroid Hormone Synthesis

DIT + MIT = T3; DIT + DIT = T4

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Thyroid Hormone Storage

Stored with thyroglobulin

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T4 to T3 Conversion

T4 is converted to T3 in peripheral tissues.

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Regulation of Thyroid Function

Production regulated by TSH. Decreased TH causes increased TSH to stimulate the thyroid gland.

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Most Sensitive Test for Hypothyroidism

Elevated serum TSH.

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Subclinical Hypothyroidism

Elevated TSH, normal free T4.

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Thyrotoxicosis

Syndrome from excessive thyroid hormone concentrations. Can be overt (high T4/T3, low TSH) or subclinical (normal T4/T3, low TSH).

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Pathophysiology of Thyrotoxicosis

Unregulated release or excessive ingestion of T4/T3, increased T4/T3 synthesis due to thyroid disease, excessive TSH, or other stimulating hormones.

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When to Consult Endocrinologist

In children/infants, difficult to maintain euthyroid state, during pregnancy, women planning to conceive, in cardiac disease.

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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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