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32 Cards in this Set

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