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Thyroid
Hypothalamic-Pituitary-Thyroid Axis
| Question | Answer |
|---|---|
| primary hypothyroidism from a lack of iodine in the diet leads to | decreased T3/T4 and increased TSH and TRH |
| t/f: a person with Graves disease has high T3/T4 production | true |
| t/f: a person with Graves disease has high TSH production | false |
| a person with Graves disease has what kind of receptors activated by thyroid-stimulating immunoglobulin | TSH |
| what is TRH | thyroid-releasing hormone that stimulates the release of TSH and PRL |
| what is somatostatin | growth hormone inhibiting hormone that inhibits GH and TSH |
| stress affect on thyroid hormone | inhibits hypothalamus from releasing TRH- TRH cannot stimulate anterior pituitary to release TSH- TSH cannot stimulate thyroid to release thyroid hormone |
| t/f: increased stress decreases thyroid hormone production | true |
| cold in infants affect on thyroid hormone | stimulates hypothalamus to release TRH which stimulates anterior pituitary to release TSH to stimulate thyroid gland to release thyroid hormone (T3/T4)- thyroid hormone acts on the anterior pituitary in a negative feedback to prevent TSH production |
| what is the primary feedback to stop TSH production from thyroid hormones on the anterior pituitary | negative feedback |
| what does thyroid hormone do | increase metabolic rate and heat production; enhance growth and CNS development, enhance sympathetic activity |
| what do follicular cells produce | T3 and T4 thyroid hormones |
| what do C cells produce | calcitonin for calcium balance |
| what is the colloid | extracellular storage for thyroid hormone |
| first step of getting thyroid hormone into circulation | tyrosine-containing thyroglobulin produced in the thyroid follicular cells by the endoplasmic reticulum-golgi complex and is transported by exocytosis into the colloid |
| second step of getting thyroid hormone into circulation | iodine is carried by secondary active transport from the blood into the colloid by symporters in the basolateral membrane of the follicular cells |
| third step of getting thyroid hormone into circulation | inside the follicular cell iodine is oxidized to it's active form by Thyroperoxidase at the luminal membrane |
| fourth step of getting thyroid hormone into circulation | active iodine exists the cells through the pendrin channel to enter the colloid |
| fifth step of getting thyroid hormone into circulation | catalyzed by Thyroperoxidase one iodine attaches to tyrosine inside the thyroglobulin to yield MIT- OR- two iodines attach to yield DIT |
| sixth step of getting thyroid hormone into circulation | coupling of one MIT and one DIT yields a T3 -OR- coupling of two DITs yield a T4 |
| seventh step of getting thyroid hormone into circulation | after correct stimulation, the thyroid follicular cells engulf a portion of the thyroglobulin-containing colloid by phagocytosis |
| eighth step of getting thyroid hormone into circulation | lysosomes attack the engulfed vesicle and split the iodinated products from thyroglobulin |
| ninth step of getting thyroid hormone into circulation | T3 and T4 diffuse into blood stream -OR- MIT and DIT are deionized and the free iodine is recycled for synthesizing more hormone |
| t/f: T3 is 10x more potent in biological activity than T4 | true |
| how much thyroid hormone is in the inactive T4 form | 93% |
| t/f: T4 (inactive) must be converted to T3 (active) before the body can use it | true |
| where in the body is 60% of T4 is converted to T3 | liver (primary site) |
| t/f: a small amount of T4 is converted to T3 in the peripheral tissues | true |
| how much T4 is converted into T3S and T3AC (inactive forms) | 20% |
| what happens to T3S and T3AC (inactive forms) | excreted or converted to active T3 via bacteria in GI tract |
| how do thyroid hormones increase the body's overall basal metabolic rate | regulate body's use of O2 energy expenditure calorigenic (heat-producing) |
| t/f: thyroid hormones can turn specific reactions on and off | false |
| t/f: thyroid hormones are responsible for synthesis and degradation of carbohydrates, fats, and proteins | true |
| sympathomimetic effects on thyroid hormone | increases target cell's responsiveness to epinephrine and norepinephrine (catecholamines)- cause proliferation of these receptors in target cells and a permissive effect |
| t/f: T3 increase responsiveness of target cells to norepi and epi | true |
| cardiovascular effects of thyroid hormones | increase heart rate and force of heart contraction increase body heat- body tries to fix this via peripheral vasodilation and carrying heat to the surface for elimination |
| effects of thyroid hormone on growth | stimulate GH secretion- ↑ effect on protein synthesis and skeletal growth- synergistic effect |
| why do thyroid deficient children have stunted growth | children not synergizing correctly |
| t/f: excess thyroid hormone leads to excess growth | false |
| t/f: thyroid hormone triggers differentiation of tissues | true |
| t/f: goiters are independent of TSH | true |
| primary hypothyroidism- failure of thyroid gland | decreased T3 & T4, increased TSH, GOITER |
| secondary hypothyroidism- hypothalamic or anterior pituitary failure | decreased T3 & T4, decreases TSH and/or TRH |
| hypothyroidism- lack of dietary iodine | decreased T3 & T4, increased TSH and TRH, GOITER |
| hyperthyroidism- abnormal presence of TSI (Graves disease) | increased T3 & T4, decreased TSH, GOITER |
| secondary hyperthyroidism- excess hypothalamic or anterior pituitary secretion | increased T3 & T4, increased TSH and/or TRH, GOITER |
| hyperthyroidism- hyper-secreting thyroid tumor | increased T3 & T4, decreased TSH |
| symptoms of hypothyroidism | ↓ overall metabolic rate, ↓ tolerance of cold, ↑ weight, ↑ fatigue, slow/weak pulse (↓ intensity and frequency), slow reflexes and mental responsiveness (↓ epi responsiveness) |
| why is there a poor tolerance to cold in hypothyroidism | lack of calorigenic effect |
| why is there a tendency to gain weight in hypothyroidism | not burning energy at normal rate |
| why do you fatigue easily with hypothyroidism | lower energy production |
| symptoms of hyperthyroidism | ↑ overall metabolic rate, ↓ tolerance of heat, ↓ weight, ↑ fatigue, heart palpitations |
| why do you fatigue easily with hyperthyroidism | increased muscle degradation |
| t/f: symptoms of hyperthyroidism are less frequent to have than hypothyrodism | true |
| t/f: thyroid receptor is a G-protein receptor | false |
| what causes heart palpitations in hyperthyroidism? | cardiac contraction and altered catecholamine responsiveness |
| why do you tend to lose weight in hyperthyroidism? | burning more energy at basal state |
| why is there a poor tolerance to heat in hyperthyroidism? | increased heat production |
Created by:
k.murski
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