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32 Cards in this Set
- Front
- Back
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Describe T3: what is its half-life? Affinity for receptor?
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T3 has a short half-life, a high affinity for the receptor, and is thought to be the biologically active form of the hormone.
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Describe T4: what's its half-life? Affinity for receptor?
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T4 has a short half life, low affinity for receptor, and is thought to be a "reserve".
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Is the structure of T3/T4 closer to the steroids or peptides?
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The steroids.
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What are the symptoms of hyperthyroidism?
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*muscular fatigue
*increased appetite w/wt loss *heat intolerance *agitation and anxiety *increased output and amenorrhea *increased heart rate, dyspnea *increased sweating, hair loss |
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What are some symptoms of hypothyroidism?
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*fatigue, lethargy
*cold intolerance *decreased appetite w/wt gain *decreased sweating, hair loss, dry skin *increased mentrual flow *decreased cardiac output |
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During what periods are T3/T4 critical for CNS development? What role do they play? What does deficiency at this time cause?
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During the final 6 prenatal mos, and the first 6 postnatal mos. Signal neuroblasts to differentiate into neurons to form pathways. Cretinism (dwarfism + MR) occurs with deficiency.
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What role does iodine play in the synthesis of T3/T4?
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It is taken up by follicular cells by a Na/I pump, and then covalently bonded to Tyr residues. This is used to form thyroglobulin.
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What is thyroglobulin?
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A large protein precursor that forms the colloid center of each follicle. Each molecule yields 3-4 molecules of T3/T4.
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How is thyroglobulin converted to T3/T4?
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It is taken up by follicular cells by pinocytosis and then split into T3/T4 in follicular lysosomes. It is then secreted into the bloodstream.
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How is T3/T4 synthesis stimulated?
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TRH is released by the hypothalamus, this causes the ant pituitary to release TSH which then stimulates the thyroid follicles.
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How is T3/T4 synthesis inhibited?
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T3 exhibits negative feedback on the release of TSH and to a small degree TRH.
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How is thyroid hormone transported in the plasma?
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70% is bound to a specific protein carrier; T4 has a greater affinity for this molecule.
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T/F:
The thyroid gland is routinely palpated during the PE and nodules can be found in ~25% of women. |
False: The gland is palpated, but nodules appear in only 4% of women.
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What happens in Graves disease? What kinds of symptoms are seen? What is the typical treatment?
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AutoAb's mimic TSH and stimulate follicular cells to release T3/T4 w/o regulation. Shows sx of hyperthyroidism. Tx is surgical.
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What happens in Hashimoto's disease? What kinds of symptoms are seen? What is the likely treatment?
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AutoAb's attack and destroy thyroid tissue. Sx of hypothyroidism are seen. Tx is hormone replacement.
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What are the 3 main organs involved with Ca++ and what do they do?
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1.Intestine: change rate of absorption of Ca from diet
2.Kidney: able to resorb or excrete Ca++ in urine. 3.Bone: resorb or form new bone. |
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What are the 3 forms of Ca in the body? Which is most important biologically?
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Ca may be in the ionic form, part of a salt, or bound to protein. The ionic form is most impt.
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Where is PTH synthesized? Is it a peptide, steroid, or amino acid hormone?
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PTH is synth by the chief cells of the parathyroid gland. It is a peptide hormone.
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What is the function (not action) of PTH?
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To elevate [Ca++] and lower [phosphate].
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Why is [phosphate] important in determining [Ca++]?
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Because phosphate is able to form a salt with Ca++ and thus reduce the amt in the ionic form.
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How is the synthesis of PTH stimulated?
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PTH is synthesized constantly but stored until the chief cells sense a drop in [Ca++]. The sensing receptor is in their plasma membranes.
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What 3 actions does PTH have on the kidney?
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*resorption of Ca++ is increased
*resorption of phosphate is decreased *synthesis of Vit D is stim |
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What are the actions of PTH on bone? (there are 3)
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*osteoclasts are stim to resorb bone
*immature osteoclasts are stim to mature *formation of new matrix is inhibited |
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What is PTH-related peptide? With what condition is it associated.
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A peptide that shares the first 13 AA residues with PTH and can stimulate PTH receptors. It causes humoral hypercalcemia of malignancy.
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What are the 2 sources of Vit D for humans?
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From the diet and synthesized in the skin upon exposure to UV light.
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What happens to Vit D in the liver?
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It is converted to the 25-OH form which can then be stored or enter circulation.
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What happens to Vit D in the kidney?
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PTH stimulates the conversion of the 25-OH form to the biologically active form.
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What symptoms are seen with Vit D deficiency?
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Poor mineralization of the bones, a.k.a. "rickets"
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Where is calcitonin synthesized?
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C (parafollicular) cells in the thyroid gland.
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T/F:
Calcitonin is an essential player in CA metabolism and is important in reversing the action of PTH. |
False: Calcitonin does oppose PTH action, but it is fairly unimportant in humans.
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Calcitonin is being explored as a tx for a common medical condition - what is it?
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Osteoporosis
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What is the action of PTH in the small intestine?
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It stimulates absorption of Ca++ from the luminal contents.
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