Thyroid Physiology Quiz
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Questions and Answers

What is the primary role of thyroid-stimulating hormone (TSH) in the thyroid gland?

  • To control the secretion of thyroid hormones (correct)
  • To regulate iodine levels in the thyroid
  • To increase the size of the thyroid gland
  • To stimulate the growth of follicular cells

    • How do thyroid hormones mainly affect the body?

  • By influencing homeostasis and development (correct)
  • By regulating blood sugar levels
  • By controlling muscle contraction
  • By stimulating adrenaline production

    • Which substance is critical for the synthesis of thyroid hormones?

  • Sodium
  • Iodine (correct)
  • Iron
  • Calcium

    • What is the main component of the colloid found in the follicular cavity of the thyroid gland?

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

    In which stage of life does the thyroid gland's function typically increase?

    <p>During pregnancy and lactation</p> Signup and view all the answers

    What histological feature primarily characterizes the thyroid gland?

    <p>Closed follicles lined with cuboidal cells</p> Signup and view all the answers

    What happens to the size of the thyroid gland when comparing males and females?

    <p>It is larger in females</p> Signup and view all the answers

    What anatomical structure connects the two lobes of the thyroid gland?

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

    What is the primary mechanism through which iodide is transported into follicular cells?

    <p>Sodium-iodide pump</p> Signup and view all the answers

    What happens to the concentration of iodide in the thyroid gland during hyperactivity?

    <p>Increases 200 times</p> Signup and view all the answers

    Which enzyme is responsible for the oxidation of iodide to elementary iodine?

    <p>Thyroid peroxidase</p> Signup and view all the answers

    What is the term for the binding of iodine with thyroglobulin in follicular cavities?

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

    Which of the following is NOT formed during the coupling reactions of iodotyrosine residues?

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

    Which forms of iodotyrosine residues are produced from the iodination of tyrosine?

    <p>Monoiodotyrosine (MIT) and di-iodotyrosine (DIT)</p> Signup and view all the answers

    What is the function of the enzyme iodinase in the thyroid hormone synthesis process?

    <p>It speeds up the iodination process</p> Signup and view all the answers

    Where are thyroid hormones stored after synthesis?

    <p>In vesicles within thyroglobulin</p> Signup and view all the answers

    What is the primary immediate effect of thyroid-stimulating hormone (TSH)?

    <p>Release of thyroxine within 30 minutes</p> Signup and view all the answers

    How does TSH primarily exert its effects on thyroid follicular cells?

    <p>Through the cyclic AMP mechanism</p> Signup and view all the answers

    Which of the following hormones regulates TSH secretion?

    <p>Thyrotropic-releasing hormone (TRH)</p> Signup and view all the answers

    What is the normal plasma level of thyroid-stimulating hormone (TSH)?

    <p>2 U/mL</p> Signup and view all the answers

    Which action is NOT increased by thyroid-stimulating hormone (TSH)?

    <p>Basal metabolic rate in the brain</p> Signup and view all the answers

    In which condition does BMR typically increase by about 60% to 100% above normal levels?

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

    What effect do thyroid hormones have on their own secretion?

    <p>Inhibit the release of TRH and TSH</p> Signup and view all the answers

    What is a key component of the calorigenic action of thyroxine?

    <p>Enhanced mitochondrial activity</p> Signup and view all the answers

    What effect does an increase in thyroid hormone levels have on protein metabolism?

    <p>Causes protein breakdown, leading to muscle weakness.</p> Signup and view all the answers

    How does thyroxine affect carbohydrate metabolism?

    <p>Enhances the absorption of glucose from the gastrointestinal tract.</p> Signup and view all the answers

    What is the primary action of thyroxine on fat metabolism?

    <p>Mobilizes fat from adipose tissues into free fatty acids.</p> Signup and view all the answers

    What effect does thyroxine have on cholesterol levels in plasma?

    <p>Decreases cholesterol through increased hepatic excretion into bile.</p> Signup and view all the answers

    In the case of thyroxine hyposecretion, what is a likely consequence regarding cholesterol?

    <p>Increased plasma cholesterol, possibly leading to atherosclerosis.</p> Signup and view all the answers

    How does thyroxine influence the number of low-density lipoprotein receptors on liver cells?

    <p>It increases the number of receptors, enhancing cholesterol secretion.</p> Signup and view all the answers

    What impact does thyroxine have on vitamin metabolism?

    <p>Increases the formation of various enzymes.</p> Signup and view all the answers

    Which of the following effects of thyroid hormone on mitochondria is correct?

    <p>It increases mitochondrial activity and ATP production.</p> Signup and view all the answers

    What is the consequence of hyperthyroidism or thyrotoxicosis on the heart?

    <p>Leads to cardiac decompensation and potential death</p> Signup and view all the answers

    How does thyroxine affect blood vessels?

    <p>Induces vasodilation through increased metabolic activities</p> Signup and view all the answers

    What condition may occur due to an excess of thyroxine's influence on the heart's contractility?

    <p>Cardiac decompensation</p> Signup and view all the answers

    What is the effect of thyroxine on respiration?

    <p>Increases the rate and force of respiration indirectly</p> Signup and view all the answers

    How does thyroxine influence gastrointestinal function?

    <p>Stimulates secretions and movement, leading to diarrhea in excess</p> Signup and view all the answers

    Which of the following statements is true about thyroxine's role in the central nervous system?

    <p>Essential for synapse development and myelination</p> Signup and view all the answers

    What impact does thyroxine have on skeletal muscle activity?

    <p>Is critical for normal muscle activity</p> Signup and view all the answers

    Which of the following factors increases due to the influence of thyroxine?

    <p>Cardiac output is significantly increased</p> Signup and view all the answers

    What is a potential outcome of thyroxine hypersecretion on muscle function?

    <p>Weakness of the muscles due to protein catabolism</p> Signup and view all the answers

    What effect does hyposecretion of thyroxine have on sleep patterns?

    <p>It results in excessive sleep lasting 12 to 14 hours a day</p> Signup and view all the answers

    How does thyroxine impact sexual function in men under hypothyroidism?

    <p>Leads to complete loss of libido</p> Signup and view all the answers

    What physiological change occurs in basal metabolic rate (BMR) during hyperthyroidism?

    <p>Increases by about 30% to 60%</p> Signup and view all the answers

    What hormone levels are typically absent in hyperthyroidism due to negative feedback?

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

    What is the effect of thyroxine-induced neuronal activity?

    <p>Fine muscular tremors</p> Signup and view all the answers

    Which menstrual issues can arise in women due to hypothyroidism?

    <p>Irregular cycle and menorrhagia</p> Signup and view all the answers

    What effect does normal thyroxine level have on physical activities?

    <p>Maintains normal muscle function and vigor</p> Signup and view all the answers

    Study Notes

    Physiology of Thyroid Gland

    • The thyroid gland is an endocrine gland, located at the base of the neck, consisting of two lobes connected by an isthmus.
    • It develops from an outpouching of the pharynx.
    • It weighs 20-40 grams in adults, with females having a larger gland than males.
    • Thyroid function fluctuates in response to hormonal changes throughout the life cycle, increasing slightly during pregnancy and lactation, and decreasing during menopause.

    Structure and Function of Thyroid Hormones

    • The thyroid gland produces three hormones: tetraiodothyronine (T4), triiodothyronine (T3), and calcitonin.
    • T4 is the primary hormone, comprising 93% of the total secretion.
    • T3 is more potent, accounting for 7-10% of the secretion.
    • Calcitonin regulates calcium levels in the body.

    Synthesis of Thyroid Hormones

    • Synthesis occurs in the follicular cells of the thyroid gland.
    • Iodine is crucial for hormone production, taken from the diet and transported into the follicle.
    • Iodine is oxidized and then incorporated into tyrosine molecules within thyroglobulin.
    • Coupling reactions combine iodinated tyrosines to form T3 and T4.

    Transport of Thyroid Hormones

    • T4 and T3 bind to transport proteins (primarily thyroxine-binding globulin, TBG) for transport in the blood.
    • T3 is more loosely bound than T4, resulting in faster release.
    • T4 has a longer half-life than T3.

    Actions of Thyroid Hormones

    • Metabolism: Increased metabolic rate, oxygen consumption, protein synthesis, and thermogenesis.
    • Cardiovascular system: Increases heart rate and force of contraction.
    • Growth: Essential for fetal brain development and overall growth.
    • Muscles: Affects protein metabolism in muscles.
    • Digestion: Increases appetite and GI activity.
    • CNS: Affects mental and physical development.
    • Reproduction: Critical for normal reproductive function, menstruation in women, and libido in men.
    • Body temperature: Influences body temperature regulation.
    • Sleep: Affects sleep patterns; high levels prevent sleep.

    Regulation of Thyroid Function

    • The hypothalamus and pituitary glands control thyroid hormone secretion.
    • Hypothalamic TRH stimulates the anterior pituitary to release TSH which then stimulates the thyroid to produce hormones.

    Thyroid Function Tests

    • Measuring T3, T4, and TSH (thyroid stimulating hormone) levels can diagnose thyroid disorders.
    • Elevated TSH indicates hypothyroidism.
    • Low TSH usually suggests hyperthyroidism.
    • These tests measure levels of TSH, T3, and T4 to diagnose issues.

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    Related Documents

    Physiology of Thyroid Gland PDF

    Description

    Test your knowledge on the roles and functions of the thyroid gland, including the importance of thyroid-stimulating hormone (TSH) and thyroid hormones. Explore key aspects such as iodide transport, colloid composition, and structural characteristics of the thyroid gland. This quiz is essential for students studying endocrinology or human physiology.

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