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23 Cards in this Set
- Front
- Back
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Notable roles of thyroid hormone
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Promote fetal/childhood development, maintain heart rate & contractility, GI motility, renal water clearance, modulate energy expenditure, heat generation, neuromuscular response
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Describe thyroid hormone synthesis
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Iodide transported into follicular cells (via Na/I cotransported) & then into colloid (by pendrin).
Follicular cells produce thyroglobulin which contains tyrosine residues, this protein moves in a vacuole & is released into the colloid Within the colloid, iodide is oxidized to iodine. The tyrosine moities on the thyroglobulin are iodinated & bind one another (mono and di) forming T3 & T4 (mostly 4). The thyroglobulin-T3/T4 complex is endocytosed and the vacuole moves back into follicular cells where proteolysis cleaves the bonds holding T3 & T4 to the thyroglobulin backbone. T3 & T4 then move through a vesicle and are secreted out of the cell into the capillary |
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Main transporter protein for T3/T4, others?
Do tissues respond to free or bound hormones? |
Thyroxine binding globulin.
Also albumin, transthyretin Bound hormones |
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T4 conversion to T3 & rT3. Which is more common? What happens?
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Formation of T3 is more common. There are 3 types of deiodinase. Types 1 and 2 are responsible for removing an iodine in such a way that T3 is formed. Type 3 forms rT3 (this pathway is more rare)
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Iodine deficiency- what happens to thyroid function
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Less T3/T4 formation > increased TSH > increased cell division > goiter & potentially hypothyroidism over time
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Amiodarone can give rise to a unique condition known as Wolf-Chaikoff effect. What happens here? Does the condition resolve?
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Amiodarone has iodine in it, causes increased iodine delivery. Therefore, the thyroid autoregulates this increased iodine load by SHUTTING DOWN TPO in the colloid (prevents massively elevated thyroid function)
The condition usually resolves, however some patients may fail to escape from the effect. Others may recover and present with HYPERthyroidism (Jod Basedow effect). |
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Effects of hyperthyroidism on HR/BP?
On bone? On neuromuscular system? |
Increase HR, vasodilate (widened pulse pressure due to decrease diastolic BP)
Increased bone resorption Increased muscle contraction, muscle weakness, hyperactivity |
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Radioactive iodine uptake scan- appearance in:
normal thyroid Graves Toxic multinodular goiter Toxic Adenoma Cold nodule |
Somewhat small, relatively diffuse uptake
LARGER, diffuse uptake Large, asymmetric uptake 1 large central area of increased uptake Photopenic- light grey |
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Most common cause of hypothyroid in the US?
Specific findings? Is it inherited? |
Hashimoto's
Often set off by environmental trigger Antibodies to Tg & TPO May have increased prevalence in families. |
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Hypothyroidism in newborns- typical findings
In children? |
NB- Cretinism, jaundice respiratory difficulties, umbilical hernia
C- growth retardation, short stature, adult sx |
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Myxedema coma- features
Treatment |
Severe hypothyroidism + precipitating illness --> change in mental status, hypotension, hypothermia, bradycardia, high TSH
Treat with T3/T4 and maybe glucocorticoids |
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Patient has really low Free T4 on examination. Should you treat this patient with T3 in addition to T4?
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Not necessary, T4 converted to T3 in peripheral circulation
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Why can pregnancy lead to hyperthyroidism?
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HCG and TSH have structural similarity. HCG binds and activates thyroid.
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What is the cause of a warm, pulsating bruit, heard at the thyroid?
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In Graves disease, the gland gets large & hyperactive leading to increased vascularity
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Finger clubbing- seen in hyper or hypothyroidism?
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Hyper
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Common treatments for hyperthyroidism due to graves?
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Beta blocker (for tachycardia), propylthiouracil/methimazole- inhibit TPO
Iodine/lithium- inhibit T3/T4 secretion |
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Similar symptoms to Graves disease, seen in older female. What should you be thinking about?
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Toxxic nodular goiter
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Thyroid storm- precipitated by?
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Seen during stressful illness
Mental status change Treat with anti-thyroid meds, beta blockers, cortisol |
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In non-thyroidal illness, what types of changes can be seen in thyroid hormone levels? How is this treated?
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Decreased function of type 1 & type 2 deiodinase, therefore more rT3 is formed and the patient will have low T3 levels (compensatory increase in TSH).
This IS NOT TREATED Just monitor thyroid function |
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Vast majority of thyroid cancer is what type?
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Papillary carcinoma
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What are the symptoms of advanced papillary carcinoma?
Treatment? |
Dysphagia, hoarseness, dyspnea
Usually removal of thyroid gland |
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Tumor marker of medullary carcinoma?
Are most sporadic or inherited? Gene involved? |
Calcitonin
Majority are sporadic. Some inherited as part of MEN2 syndrome Gain of fxn mutation of RET oncogene. |
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Most aggressive thyroid cancer?
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Anaplastic carcinoma
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