Medicine Marrow Pg No 895-904 (Endocrinology)
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Questions and Answers

What is the primary function of Thyroglobulin in the thyroid follicle?

  • Storing thyroid hormone precursors (correct)
  • Regulating metabolism
  • Secreting calcitonin
  • Stimulating the pituitary gland

    • The thyroid follicle is primarily composed of parafollicular cells.

    False

    What stimulates the thyroid gland to produce T3 and T4 hormones?

    TSH (Thyroid-stimulating hormone)

    The deficiency in _______ can lead to congenital hypothyroidism.

    <p>TTF-1 or TTF-2</p> Signup and view all the answers

    Match the following transcription factors with the defects they lead to:

    <p>TTF-1 = Congenital Hypothyroidism TTF-2 = Congenital Hypothyroidism PAX-8 = Congenital Hypothyroidism PROP-1 = Combined pituitary hormone deficiency</p> Signup and view all the answers

    What is the primary purpose of TSH in thyroid hormone synthesis?

    <p>To stimulate the thyroid gland</p> Signup and view all the answers

    The primary product of iodination in thyroid hormone synthesis is T4.

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

    What is the role of the Na+-I symporter in thyroid hormone production?

    <p>It facilitates iodide uptake.</p> Signup and view all the answers

    Thyroglobulin is an enzyme-independent component in the synthesis of __________.

    <p>thyroid hormones</p> Signup and view all the answers

    Match the following thyroid-related terms with their descriptions:

    <p>Thyroid peroxidase = Enzyme responsible for iodination Amiodarone = Medication associated with thyrotoxicosis DUOX2 = Protein involved in hydrogen peroxide generation Pendrin = Protein essential for iodide transport</p> Signup and view all the answers

    Which carrier protein has the highest percentage in transporting thyroid hormones?

    <p>TBG (Thyroid Binding Globulin)</p> Signup and view all the answers

    Thyrotoxicosis is characterized by increased levels of free T₃ and free T₄.

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

    What is the primary defect associated with Allan-Herndon-Dudley Syndrome?

    <p>MCT8 Defect</p> Signup and view all the answers

    In conditions of euthyroid hyperthyroxinemia, one potential cause is excessive levels of _____ in the bloodstream.

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

    Match the thyroid function disorders with their characteristics:

    <p>Hyperthyroxinemia = Increased T₃ and T₄ levels Thyrotoxicosis = Increased free T₃ and free T₄ levels Resistance to Thyroid Hormone (RTH) = Uninhibited increase in TSH Euthyroid Hyperthyroxinemia = Normal thyroid function with elevated hormone levels</p> Signup and view all the answers

    Which iodine isotope is primarily used for radioablation in Graves' disease?

    <p>¹³¹I</p> Signup and view all the answers

    The usual daily recommended amount of iodine for adults is 220 µg.

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

    What effect does hyperthyroidism have on basal metabolic rate (BMR)?

    <p>Increases BMR</p> Signup and view all the answers

    What is the principal enzyme responsible for the peripheral conversion of T3?

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

    Hypothyroidism is associated with increased heart rate.

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

    What is the effect of the thyroid gland on cholesterol clearance during hypothyroidism?

    <p>Hypothyroidism leads to hypercholesterolemia.</p> Signup and view all the answers

    Di-type II deiodinase is most abundant in the ______.

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

    Match the deiodinase inhibitors with their correct names:

    <p>Propylthiouracil = Inhibits thyroid hormone production Amiodarone = Antiarrhythmic medication affecting thyroid function Steroids = Immunosuppressants that can alter hormone metabolism Propranolol = Beta-blocker with effects on thyroid hormones</p> Signup and view all the answers

    The thyroid gland is responsible for _______ of the central nervous system (CNS).

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

    During the early stage of sick euthyroid syndrome, what happens to T4 levels?

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

    Match the following conditions with their associated effects:

    <p>Hypothyroidism = Decreased basal metabolic rate Hyperthyroidism = Increased cardiac output Toxicosis = Increased peripheral resistance Myxedema coma = Hypothermia</p> Signup and view all the answers

    What should not be done during critical illness in relation to TFT?

    <p>TFT testing should not be performed.</p> Signup and view all the answers

    The half-life of T3 is ______, while T4 is ______.

    <p>1 day, 1 week</p> Signup and view all the answers

    Which of the following is NOT a rheumatological cause of hypogonadal states?

    <p>Cushing disease</p> Signup and view all the answers

    A T-score of -1.8 indicates osteoporosis.

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

    What is the classic sign in osteoporosis that resembles a codfish mouth?

    <p>Codfish/fish mouth sign</p> Signup and view all the answers

    A __________ scan is used to assess bone density and score trabecular bone.

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

    Match the following conditions with their related T-score diagnosis:

    <p>-1 to -2.5 = Osteopenia ≤ -2.5 = Osteoporosis ≤ -2.5 with fracture = Severe Osteoporosis</p> Signup and view all the answers

    What is the earliest symptom of osteoporosis?

    <p>Back pain</p> Signup and view all the answers

    Osteoporosis primarily affects males more than females.

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

    Name one of the most common types of fractures associated with osteoporosis.

    <p>Neck of Femur</p> Signup and view all the answers

    Osteoporosis is characterized by low bone mass and quality, leading to micro-architectural __________.

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

    Match the following risk factors with their corresponding categories:

    <p>Smoking history = Lifestyle Early menopause = Hormonal Steroids = Medication Low calcium intake = Nutritional</p> Signup and view all the answers

    Which artery primarily supplies blood to the thyroid gland?

    <p>Superior thyroid artery</p> Signup and view all the answers

    The thyroglossal duct should disappear completely after 5 weeks of gestation.

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

    What is the common location for a thyroglossal cyst?

    <p>Subhyoid position</p> Signup and view all the answers

    The thyroid gland migrates from the floor of the primitive pharynx to _________ the trachea.

    <p>anterior to</p> Signup and view all the answers

    Match the following structures with their respective functions:

    <p>Superior laryngeal nerve = Internal branch and external branch innervation Recurrent laryngeal nerve (R) = Innervates the right side of the larynx Recurrent laryngeal nerve (L) = Innervates the left side of the larynx Thyroglossal tract = Formed from pretracheal fascia</p> Signup and view all the answers

    Which of the following is the first choice antiresorptive drug for osteoporosis?

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

    Denosumab is a first-line treatment for osteoporosis.

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

    What is the recommended amount of daily calcium intake for supportive care in osteoporosis?

    <p>1200 mg</p> Signup and view all the answers

    The side effects of bisphosphonates include _______ necrosis of the jaw.

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

    Match the following drugs to their primary characteristics:

    <p>Alendronate = Oral bisphosphonate Raloxifene = SERM with agonistic effects Teriparatide = Recombinant PTH for bone formation Romosozumab = Sclerostin inhibitor</p> Signup and view all the answers

    In primary hypothyroidism, what are typically elevated levels of thyroid hormones?

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

    In critically ill patients, it is essential to always check T3 and T4 levels.

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

    What is the normal range for TSH as defined by CLIA 4th generation?

    <p>0.5 - 5 mIU/L</p> Signup and view all the answers

    In subclinical primary hypothyroidism, the TSH level is _____ while FT3 and FT4 remain normal.

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

    Match the drug with its effect on thyroid hormone levels:

    <p>Amiodarone = Inhibits deiodinase Propranolol = Suppresses T4 secretion Phenytoin = Increases hormone metabolism Cholestyramine = Decreases hormone absorption</p> Signup and view all the answers

    Which condition is associated with decreased TSH and normal FT3 and FT4 levels?

    <p>Subclinical hyperthyroidism</p> Signup and view all the answers

    Thyroglobulin levels increase in all thyrotoxicosis instances except in thyrotoxicosis factitia.

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

    Name one condition associated with elevated TSH and decreased T3 and T4 levels.

    <p>Primary hypothyroidism</p> Signup and view all the answers

    Study Notes

    Thyroid Follicle

    • The thyroid follicle is the functional and structural unit of the thyroid gland.
    • The follicular epithelial cells line the follicle and are responsible for hormone production.
    • Colloid is the material within the follicle that contains thyroglobulin, a protein that stores thyroid hormone precursors.
    • Thyroglobulin is formed by the 29th day of gestation and is the first hormone precursor.
    • Hormone synthesis begins by the 11th week of gestation.
    • Thyroid-stimulating hormone (TSH) from the pituitary gland stimulates the production of thyroid hormones T3 and T4.
    • Parafollicular/C-cells in the thyroid secrete calcitonin.
    • Transcription factors like TTF-1, TTF-2, PAX-8, and PROP-1 are crucial for thyroid gland development.
    • Deficient TSH (as in hypopituitarism) can result in minimal to no hypothyroidism.

    Basics of Thyroid Gland

    • ¹³¹I is used for radioablation in Grave's disease.
    • ¹²³I is used for brachytherapy.
    • The recommended daily intake (RDA) of iodine is 150 µg/day for adults, 220 µg/day for pregnant women.
    • Repleting iodine levels require a daily urinary excretion of iodine >100 µg.

    Deiodinase Enzyme

    • Di-type II (most abundant) is the primary enzyme for peripheral conversion of T4 to T3.
    • Deiodinase inhibitors include propylthiouracil, amiodarone, steroids, and propranolol.

    SICK EUTHYROID SYNDROME / LOW T3 SYNDROME

    • Thyroid function tests (TFTs) should not be performed in patients with critical illness, systemic illness, or fasting for a few days.
    • Deiodinase type 1 (D1) is inhibited and Deiodinase type 3 (D3) is activated in this syndrome.
    • The stages of the syndrome are:
      • Early stage: Increased T4, normal T3, and increased reverse T3 (rT3)
      • Middle stage: Decreased TSH, increased rT3, decreased T3, increased T4.
      • Late stage: Rapid catabolism of all hormones, decreased T4, decreased TSH, decreased rT3, decreased T3.

    Hormone Synthesis and Release

    • TSH binds to the TSH receptor on the thyroid gland.
    • Organification, iodination, and coupling are key steps in thyroid hormone synthesis.
    • The final hormones T3 and T4 are released from the thyroid gland in a ratio of 10:1.
    • T4 is converted peripherally to T3, the active form, accounting for 80% conversion and 20% synthesis.

    Osteoporosis

    • Osteoporosis is a loss of bone strength caused by a defect in bone quantity and quality.
    • The earliest symptom is back pain.
    • Postmenopausal women have the highest prevalence of osteoporosis.
    • Most characteristic symptoms include fractures (neck of femur, hip bone, vertebral fracture, Colles' fracture).
    • Distal forearm fractures are a sensitive marker of bone fragility in men.

    Thyroid Function Tests

    • Increased T3 and T4 levels constitute hyperthyroxinemia.
    • Increased free T3 and free T4 levels indicate thyrotoxicosis.
    • Thyroid function tests are not recommended in critically ill patients.

    Thyroid Function and Body Processes

    • Thyroid hormones regulate the basal metabolic rate (BMR), cardiac actions, oxygen utilization, and heart rate.
    • Hypothyroidism causes a decrease in BMR, while hyperthyroidism causes an increase.
    • Hypothyroidism can contribute to insulin resistance, hypercholesterolemia, menorrhagia, infertility, myopathy, osteopenia, and osteoporosis.
    • Hyperthyroidism can cause hypercalcemia, hypercalciuria, and kidney stones.

    Endocrinology

    • Many conditions can result in secondary hypothyroidism including:
      • GI disease (e.g., celiac disease)
      • Hypogonadal states (e.g., hyperprolactinemia, Turner's syndrome, Klinefelter syndrome)
      • Rheumatological causes (e.g., ankylosing spondylitis, rheumatoid arthritis, sarcoidosis)
      • Endocrine causes (e.g., Cushing disease, hyperparathyroidism, diabetes insipidus, acromegaly, thyrotoxicosis)
      • Inherited diseases (e.g., porphyria, hemochromatosis, homocystinurea, Marfan's, sickle cell anemia, hemophilia)

    Management of Osteoporosis

    • Supportive care includes smoking cessation, Vitamin D3 intake, calcium intake, and increased physical activity.
    • Bisphosphonates are the first choice for antiresorptive therapy.
    • Denosumab is a RANK-L inhibitor used as a third-line therapy.
    • Teriparatide and Abaloparatide are recombinant PTH therapies.
    • Other drugs that may help manage osteoporosis include hormone replacement therapy, strontium ranelate, calcitonin, raloxifene, and newer medications like odanacatib, saracatinib, and romosozumab.

    Basics of Thyroid Gland

    • The thyroid gland is the first endocrine organ to form during embryonic development (3-4 weeks of gestation) and is derived from the endoderm.
    • It migrates from the floor of the primitive pharynx to the anterior of the trachea.
    • The blood supply is from the superior thyroid artery and the inferior thyroid artery.
    • The recurrent laryngeal nerves (right and left) are located close to the inferior thyroid artery.
    • The thyroid gland is innervated by the superior laryngeal nerve.

    Thyroglossal Cyst

    • Thyroglossal cysts are remnants of the thyroglossal duct that persist beyond 5 weeks of gestation.
    • The location is often subhyoid, which is the most common position.
    • Thyroglossal cysts can protrude with tongue movement and deglutition.
    • The cyst can move upward and backward when the tongue protrudes.
    • The cyst has a pseudocapsule formed by pretracheal fascia.

    Supportive care and Drug used:

    • Supportive care for osteoporosis includes smoking cessation, calcium intake, vitamin D3, and increased physical activity.
    • Bisphosphonates are the first choice for antiresorptive therapy of osteoporosis.
    • Oral bisphosphonates include Alendronate and Risedronate.
    • Denosumab is a RANK-L inhibitor used as a third-line therapy.
    • Teriparatide and Abaloparatide are recombinant PTH therapies.
    • Other drugs that may help manage osteoporosis include hormone replacement therapy, strontium ranelate, calcitonin, raloxifene, and newer medications like odanacatib, saracatinib, and romosozumab.
    • Zoledronate and Ibandronate are used for definitive care.

    Thyroid Function Tests

    • TFTs should always check for free T3 (fT3) and free T4 (fT4).
    • The normal TSH range is 0.5- 5 mIU/L.
    • Drug-induced changes to TFTs may require adjustments to medications and dosages:
      • Deiodinase inhibitors (e.g., propylthiouracil, amiodarone, steroids, Propranolol)
      • lodine (e.g., amiodarone, propylthiouracil)
      • Enzyme inducers (e.g., phenytoin, carbamazepine, rifampicin)
      • Drugs that reduce hormone absorption (e.g., aluminum hydroxide, cholestyramine, calcium carbonate, ferrous sulfate)
      • Drugs with effects on thyroid function (e.g., sertraline, ritonavir).

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    Description

    This quiz explores the structure and function of thyroid follicles, including hormone synthesis and key factors involved. Understand the roles of TSH and calcitonin in thyroid gland activity and development. Test your knowledge on the basics of thyroid hormones and their precursors.

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