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19 Cards in this Set
- Front
- Back
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What are the iodine containing hormones that control the body's metabolic rate?
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Thyroid Hormones: T3/T4
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What is the source of the thyroid hormones (T3/T4)?
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- Follicles of thyroid
- Most T3 formed in target tissues |
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What are the functions of thyroid hormones?
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- Bone growth (synergism with GH)
- CNS maturation - ↑ CO, HR, SV, contractility - ↑ Basal metabolic rate - ↑ Glycogenolysis, gluconeogenesis, lipolysis |
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How do thyroid hormones affect the heart? Effects?
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↑ β1 receptors in heart → ↑ CO, HR, SV, contractility
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How do thyroid hormones affect the basal metabolic rate? Effects?
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↑ BMR by ↑ Na+/K+ ATPase activity → ↑ O2 consumption, RR, and body temperature
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What are the effects of thyroid hormones on energy storage?
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↑ Glycogenolysis, gluconeogenesis, and lipolysis
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What is the mnemonic to remember the T3 functions?
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T3 functions - 4 B's:
- Brain maturation (CNS) - Bone growth - β-adrenergic effects (↑ β1 receptors) - Basal metabolic rate ↑ |
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What binds the thyroid hormones in the blood? What hormones are active?
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- Thyroxine-binding globulin (TBG) binds most T3/T4 in the blood
- Only the free hormone is active |
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What can decrease the amount of Thyroxine-Binding Globulin (TBG)?
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Hepatic Failure
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What can increase the amount of Thyroxine-Binding Globulin (TBG)?
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Pregnancy or OCP use (estrogen ↑ TBG)
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What is the major thyroid product? What happens to it?
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- T4 is the major thyroid product
- Converted to T3 in peripheral tissue by 5'-deiodinase |
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What enzyme converts T4 to T3 in the peripheral tissues?
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5'-deiodinase
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Which form of the thyroid hormones can bind receptors with greater affinity?
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T3 binds receptors with greater affinity than T4 |
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What enzyme is responsible for oxidation and organification of iodide?
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Peroxidase
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What enzyme is responsible for coupling of monoiodotyrosine (MIT) and diodotyrosine (DIT)?
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Peroxidase
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What drug can inhibit both peroxidase and 5'-deiodinase?
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Propylthiouracil
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What drug can inhibit peroxidase but not 5'-deiodinase?
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Methimazole
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What regulates Thyroid Hormones (T3/T4)?
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- TRH (hypothalamus) stimulates TSH (pituitary), which stimulates follicular cells
- Negative feedback by T3, T4 to anterior pituitary ↓ sensitivity to TRH - Thyroid stimulating immunoglobulins (TSIs), like TSH, stimulate follicular cells (eg, Graves disease) |
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What is the name of the effect when excess iodine temporarily inhibits thyroid peroxidase? Effect?
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Wolff-Chaikoff effect:
- ↓ Iodine organification → ↓ T3/T4 production |
