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25 Cards in this Set
- Front
- Back
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What are the 3 steps in the Hypothalamic-Pituitary-Thyroid (HPT) axis that results in the release of thyroid hormone?
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1- Paraventricular nucleus of hypothalamus releases Thyrotropin Releasing Hormone (TRH) into portal capillaries & Anterior Pituitary
2. Anterior Pituitary cells release Thyroid Stimulating Hormone (TSH) into general circulation 3. Thyroid gland cells respond to TSH by releasing thyroid hormone (T3, T4) into circulation |
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Where in the body is the thyroid gland located?
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Between thyroid cartilage down to 6th tracheal cartilage ring
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What is the functional unit of the the thyroid?
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The follicle
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What does a thyroid follicle consist of and what is the function of each region?
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- Vesicle of cuboid cells (incorporate iodine; synthesize thyroglobulin)
- Colloid interior (synthesizes T3 & T4, and stores them bound to thyroglobulin) |
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For how long can T3 & T4 be stored in the lumen of a thyroid follicular cell?
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2-3 months
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T3 = ?
T4 = ? |
T3 = Triiodothyronine
T4 = Thyroxine |
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T3 & T4 are formed by combining what 3 substances?
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Tyrosine + Iodine + Thyroglobulin
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Coupling of ___ and ___ forms T3 and T4.
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Coupling of MIT (mono-iodotyrosine) and DIT (di-iodotyrosine) forms T3 and T4.
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How is thyroid hormone released from thyroid follicular cells?
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TSH signals release
- Hormone is endocytosed via pseudopodia of follicular cells. - Thyroglobulin is degraded to amino acids. - T3, T4 released into blood |
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In what ratio is T4 and T3 released into the blood?
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T4 to T3 is 10: 1
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T4 is converted to ___ within cells.
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T4 is converted to T3 within cells.
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The feedback of what hormone inhibits TSH secretion? How does it do this?
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T3 feedback inhibits TSH secretion by down-regulating anterior pituitary cell's sensitivity to TRH.
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Cold (increases / decreases) TRH release via hypothalamic temperature centers.
Heat from metabolism (increases / decreases) TRH release. |
Cold INCREASES TRH release via hypothalamic temperature centers.
Heat from metabolism DECREASES TRH release. |
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True/False
T3 effects every organ of the body. |
TRUE!
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This condition is due to an early thyroid deficiency, resulting in abnormal development of bones & CNS; stunted growth; malformation of facial bones; mental retardation.
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Cretinism
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Name some ways that T3 enhances the basal metabolic rate (BMR).
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- Increases oxidative metabolism
- Up regulation (transcription & synthesis) of ATP-ase leads to increased O2 consumption & greater utilization of E |
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T3 facilitates ___ actions on glucose, lipids, protein metabolism.
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T3 facilitates HORMONAL actions on glucose, lipids, protein metabolism.
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T3 increases cardiac output by up regulating ___.
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T3 increases cardiac output by up regulating BETA RECEPTORS.
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What are some possible cause of Hyperthyroidism?
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- Reduced sensitivity of feedback
-Autoimmune: antibodies to thyroid gland (thyroid-stimulating immunoglobulin- TSI) release excess T3 &T4 which inhibits TSH release) |
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Name some symptoms of Hyperthyroidism.
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- Goiter (hyperplasia of thyroid cells)
- Intolerance to heat - Weight loss (decreased fat stores) - Exophthalmos (protrusion of eyes due to lid lag) - Nervousness, hand tremor - Irritability, insomnia - Tachycardia, arrhythmias |
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What are some possible causes of Hypothyroidism?
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- Autoimmune destruction, often with thyroiditis
-Iodine deficiency -Dietary goitrogens (turnips & cabbages) |
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In this condition, T3, T4 levels are low while TSH levels are high.
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Hypothyroidism- due to less negative feedback on hypothalamus & pituitary
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In hypothyroidism, there is increased ____ due to increased TSH activity but no secretion of T3, T4.
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In hypothyroidism, there is increased COLLOID due to increased TSH activity but no secretion of T3, T4.
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In this condition, T3, T4 levels are high, TSH is low.
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Hyperthyroidism
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The following are symptoms of what condition:
-Colloid goiter -Cold intolerance -Fatigue, somnolence, slow speech, lack of initiation -Delayed tendon reflex -Bradycardia -High cholesterol -Hair loss, Dry coarse skin, husky voice -Enlarged liver, kidney, tongue -Myxedema (non-pitting edema) |
Hypothyroidism
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