Podcast
Questions and Answers
What is the primary mechanism for the formation of T3 in the body?
What is the primary mechanism for the formation of T3 in the body?
- Deiodination of T4 in peripheral tissues such as the liver and kidneys. (correct)
- Condensation of one DIT and one MIT molecule within the thyroid gland.
- Direct synthesis from two DIT molecules in the thyroid follicle.
- Secretion of T3 directly from the thyroid at a rate of 80 g/day.
Which plasma protein has the highest affinity for T4, despite having the smallest binding capacity?
Which plasma protein has the highest affinity for T4, despite having the smallest binding capacity?
- Iodotyrosine deiodinase
- Albumin
- Prealbumin (Transthyretin)
- Thyroxine-binding globulin (TBG) (correct)
What is the fate of the remaining DIT & MIT within the thyroid follicle that are not immediately used for T3 or T4 synthesis?
What is the fate of the remaining DIT & MIT within the thyroid follicle that are not immediately used for T3 or T4 synthesis?
- They are catabolized and excreted in urine.
- They are secreted directly into the bloodstream.
- They are stored indefinitely within the follicle for later use.
- They are deiodinated to recover iodine and tyrosine for hormone synthesis. (correct)
Which of the following statements accurately describes the relationship between free and bound thyroid hormones in plasma?
Which of the following statements accurately describes the relationship between free and bound thyroid hormones in plasma?
If the production of reverse T3 (rT3) was blocked, how would T4 metabolism be affected?
If the production of reverse T3 (rT3) was blocked, how would T4 metabolism be affected?
What is the primary function of thyroid metabolic hormones (T3 and T4) in the body?
What is the primary function of thyroid metabolic hormones (T3 and T4) in the body?
What is a potential consequence of hypothyroidism in adult life?
What is a potential consequence of hypothyroidism in adult life?
Which of the following statements accurately describes the relationship between T3 and T4?
Which of the following statements accurately describes the relationship between T3 and T4?
During thyroid hormone synthesis, what is the role of thyroglobulin?
During thyroid hormone synthesis, what is the role of thyroglobulin?
What is the function of thyroid peroxidase enzymes in thyroid hormone production?
What is the function of thyroid peroxidase enzymes in thyroid hormone production?
How long does the colloid serve as a reservoir for thyroid hormones?
How long does the colloid serve as a reservoir for thyroid hormones?
What is the first step in the synthesis of thyroid hormone production
What is the first step in the synthesis of thyroid hormone production
Which of the following best describes the structure of thyroglobulin?
Which of the following best describes the structure of thyroglobulin?
Flashcards
Thyroid gland
Thyroid gland
Butterfly-shaped gland in front of the neck, largest endocrine gland.
Metabolic hormones (T4 & T3)
Metabolic hormones (T4 & T3)
Thyroid hormones that regulate metabolism, O2 consumption, and influence body mass.
Hypothyroidism
Hypothyroidism
Condition resulting in mental/physical slowing and cold intolerance.
Hyperthyroidism
Hyperthyroidism
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Thyroglobulin
Thyroglobulin
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Iodination
Iodination
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Thyroid peroxidase
Thyroid peroxidase
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Colloid
Colloid
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T4 Formation
T4 Formation
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T3 Formation
T3 Formation
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Thyroid Hormone Distribution
Thyroid Hormone Distribution
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Plasma Protein Binding
Plasma Protein Binding
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T4 Metabolism
T4 Metabolism
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Study Notes
Thyroid Gland
- The thyroid gland is a butterfly-shaped structure located in the front of the neck.
- It is one of the largest endocrine glands in the body.
- It secretes metabolic hormones (T4 and T3) and calcitonin.
- T4 is the primary secreted hormone; T3 is biologically active.
Thyroid Hormone Synthesis and Secretion
- Thyroid hormones are iodinated.
- T4 (thyroxine) has four iodine atoms, T3 (triiodothyronine) has three.
- Thyroid hormones are synthesized from tyrosine amino acids.
- Steps in synthesis include iodine transport, oxidation, iodination of tyrosine, endocytosis of thyroglobulin, and thyroid hormone release.
- Thyroglobulin is a glycoprotein containing tyrosine.
- Thyroid peroxidase is a membrane-bound enzyme that oxidizes iodine and couples it with tyrosine.
Thyroid Metabolic Hormones
- Function:
- Stimulate oxygen consumption in body cells.
- Regulate lipid and carbohydrate metabolism.
- Influence body mass and mentation.
- Dysfunction:
- In fetal/neonatal life: Absence or hypofunction leads to severe mental retardation and dwarfism.
- In adulthood:
- Hypothyroidism: Mental and physical slowing, cold intolerance.
- Hyperthyroidism: Body wasting, nervousness, tachycardia, tremor, excess heat production.
Thyroid Hormones in Normal Adult Humans
- Secretion rates:
- T4: 80 µg/day
- T3: 4 µg/day
- RT3: 2 µg/day
- Most T₃ and RT₃ are formed in tissues by deiodination of T₄.
- T₄ is conjugated and excreted.
Thyroid Hormone Transport
- Thyroid hormones are primarily bound to plasma proteins (TBG, prealbumin, albumin).
- The bound form acts as a reservoir.
- The free form of the hormone is biologically active.
- Normal plasma levels of T4 are around 8 µg/dL, and T3 is about 0.15 µg/dL.
Thyroid Hormone Metabolism
- T₄ is deiodinated to T₃ in the periphery.
- T₃ and T₄ participate in metabolism, and activation.
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