Term
| Where are thyroid hormones stored? |
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Definition
| First in colloid-filled follicles, then, after secretion, they are stored in the target cells for days of weeks |
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Term
| Which cells in the thyroid gland secrete thyroid hormones? |
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Definition
| the cuboidal epithelial cells that line the follicles |
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Term
| What are is the major constituent of the colloid in thyroid follicles? |
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Definition
|
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Term
| What are the hormones secreted by the thyroid gland? |
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Definition
| calcitonin, thyroxine, and triiodothyronine (T3) |
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Term
| What is the function of calcitonin? |
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Definition
| it assists in bone deposition, reducing blood calcium levels |
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Term
| What kind of hormone are T4 and T3? Steroid, peptide, gas, amine derivative, or eicosanoid? |
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Definition
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Term
| Which is secreted in higher quantities: T4 or T3? |
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Definition
|
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Term
| How are thyroid hormones transported? |
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Definition
| T4 and T3 are transported almost entirely by plasma proteins, such as thyroid-binding protein and albumin |
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Term
| The intake of a certain mineral is very important for the synthesis of thyroid hormones. Which mineral is this, how much needs to be taken in per year? |
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Definition
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Term
| How do most people, especially in America, get enough iodide in their diet? |
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Definition
| through tablet salt, which is iodinized |
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Term
| How is iodide get from the blood stream to the follicle cells? |
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Definition
| It is transported into the thyroid cells via a sodium-iodide symporter, then it is oxidized by thyroid peroxidase into I2, then transported into the follicle by pendrin (the chloride-iodine counter transporter) |
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Term
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Definition
| The coupling of iodine to thyroglobulin (on the tyrosine residues) |
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Term
| What thyroid molecules form in the synthesis process in thyroid follicles? |
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Definition
| MIT, DIT, RT3, T3, and T4 |
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Term
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Definition
| A biologically inactive isomer of T3 |
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Term
| What does the body do with the unused end products of thyroid hormone synthesis? |
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Definition
|
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Term
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Definition
| concentrating a large amount of iodide in the cell (via the symporter) |
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Term
| How much thyroid hormone is stored in the thyroid gland? |
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Definition
| enough to last about 2-3 months |
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Term
| How does the thyroid gland secrete hormones from the storage follicles? |
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Definition
| a vesicle forms via pinocytosis from the follicle; the vesicle is combined with a lysosome, which has enzymes to digest the thyroglobulin and colloid around the hormones, and the hormones are free to diffuse out of the cells into the blood |
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Term
| What is the approximate half-life of T3 and T4? Why is there a disparity between there two similar molecules? |
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Definition
| 1 day and 6 days, respectively; T4 has a greater affinity for the binding proteins in the blood |
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Term
| What is the general function of thyroid hormone in cells? |
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Definition
| ↑ functional activity, ↑ metabolism, and ↑ transcription, which leads to ↑ protein formation |
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Term
| What is the effect of thyroid hormone on body temperature? Energy consumption? Vitamin requirements? |
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Definition
| increase, increase, increase |
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Term
| What is the effect of thyroid hormone on basal metabolic rate? Heart rate? Does it vasodilate or vasoconstrict? |
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Definition
| increase, increase, vasodilate |
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Term
| What is the effect of thyroid hormone on glycogenolysis? Gluconeogensis? Blood glucose? |
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Definition
| increase, increase, increase |
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Term
| What is the effect of thyroid hormone on blood glucose uptake? Glucose absorption? Glycolysis? |
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Definition
| increase, increase, increase |
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Term
| What is the effect of thyroid hormone on lipolysis? Lipogensis? Beta oxidation? |
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Definition
| increase, increase, increase |
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Term
| What is the effect of thyroid hormone on serum [cholesterol]? Cholesterol secretion into the bile? |
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Definition
|
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Term
| What is the effect of thyroid hormone on protein catabolism? Blood flow? What will high levels of thyroid hormone cause with both of these? |
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Definition
| increase, increase; high levels of thyroid hormone will cause muscle wasting and weakness and flushing |
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Term
| What is the effect of thyroid hormone on mitochondria number? Mitochondria size? Na-K-ATPase? |
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Definition
| increase, increase, increase |
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Term
| What is the effect of thyroid hormone on heart contractility? |
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Definition
|
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Term
| How does thyroid hormone probably decrease LDL levels in the blood? |
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Definition
| It probably increases LDL receptors in the liver, which will then cause the increased filtration of LDL |
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Term
| If thyroid hormone increases heart contractility, why do many hyperthyroid patients die of cardiac decompensation? |
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Definition
| prolonged high levels of thyroid hormone leads to protein catabolism, leading to muscle wasting, which means the heart will be getting weaker |
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Term
| What is the effect of thyroid hormone on MAP? Pulse pressure? |
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Definition
| no significant effect; increase |
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Term
| What is the effect of thyroid hormone on respiration rate? Depth of breath? |
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Definition
| indirectly increase, indirectly increase |
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Term
| What is the effect of thyroid hormone on rate of secretion in the GI tract? GI motility? What will high levels of thyroid hormone cause there? |
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Definition
| increase, increase; high levels will cause diarrhea |
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Term
| What is the effect of thyroid hormone on the activity of other endocrine glands? |
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Definition
|
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Term
| What is the effect of thyroid hormone on the CNS's excitability/cebebration? What happens n the CNS with prolonged high levels of thyroid hormone? |
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Definition
| increased excitability, increased cerebration; excessive rapidity in cerebration in hyperthyroid patients may cause extreme nervousness, worry, anxiety, and psychosis |
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Term
| What is the effect of thyroid hormone on muscle vigor? What do prolonged high levels of thyroid hormone cause here? |
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Definition
| increased vigor; prolonged high levels causes muscle tremors and muscle wasting |
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Term
| What is the effect of hyperthyroidism on sleep cycle? What about hypothyroidism? |
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Definition
| tiredness accompanied with insomnia; lethargy |
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Term
| What is the effect of thyroid hormone on the pancreas activity? |
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Definition
| Thyroid hormone increases blood glucose, which will cause an increase of pancreas activity to produce insulin; |
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Term
| What is the effect of thyroid hormone on the activity of the adrenal glands? |
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Definition
| thyroid hormone increases the rate at which glucocorticoids are cleared by the liver, causing feedback to cause the production of more CRH, ACTH, and glucocorticoids |
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Term
| What is the effect of thyroid hormone on parathyroid activity? |
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Definition
| thyroid hormone increases the bone formation activities, meaning there is an increase in parathyroid hormone needs to deposition calcium for bone formation |
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Term
| What is the effect of high levels of thyroid hormone on sexual function in men? What about women? |
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Definition
| In men, high levels can cause impotence; in women, high levels can cause reduced bleeding (oligomenorrhea) or a lack of period (amenorrhea) |
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Term
| What is the effect of low levels of thyroid hormone on sexual function in men? What about women? |
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Definition
| In men, low levels can cause reduced libido; in women, low levels can cause reduced libido and a lack of period, irregular bleeding, frequent bleeding (polymenorrhea), or excessive bleeding (menorrhagia) |
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Term
| What is the effect of thyroid hormone on bone growth in children? |
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Definition
| Thyroid hormone works in conjunction with hGH to encourage bone growth |
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Term
| What is the effect of thyroid hormone on infant development? |
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Definition
| Thyroid hormone is critical to infant brain development; in utero, a baby does not need to produce thyroid hormone, because it can subsist off of maternal thyroid hormone; however, unless it has thyroid hormone (produced by itself or supplemented), it will be permanently mentally retarded |
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Term
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Definition
| Cretinism is mental retardation due to the lack of thyroid in infancy to assist with mental development; children with cretinism may develop stocky, short, and obese-looking, due to the lack of hGH due to the lack of thyroid hormone to stimulate the secretion of hGH; there children sometimes develop enlarged tongues and have to compensate with guttural breathing patterns that sometimes choke the child |
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Term
| What happens to a a child's bone growth if he has hyperthyroidism? What about hypothyroidism? |
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Definition
| high levels of thyroid hormone causes rapid bone growth, meaning the child will become taller quickly, and early fusing of the epiphyseal plates (meaning there will be an overall stunted growth); low levels of thyroid hormone means the child may develop stocky, short, and obese-looking, due to a lack of thyroid hormone to stimulate the secretion of hGH |
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Term
| What hormone most affects thyroid hormone secretion? |
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Definition
| thyroid stimulating hormone (TSH) |
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Term
| What effect(s) does TSH have on the thyroid gland? |
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Definition
| TSH increases the size and activity of thyroid cells, increases the proteolysis of thyroglobulin in the follicles, increases the activity of the iodide pump (leading to increased iodide trapping), increases the number of thyroid cells (changing cuboidal cells into columnar cells in hyperthyroidism), and maintains the size and activity of the gland itself |
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Term
| What is the second messenger for TSH's stimulation of the thyroid gland? |
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Definition
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Term
| What stimuli stimulate the release of TRH from the hypothalamus? |
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Definition
| cold, excitement, anxiety |
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Term
| What is the feedback mechanism for thyroid hormone secretion? |
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Definition
| Stimuli stimulate the release of TRH stimulates the release of TSH, TSH stimulates the release of thyroid hormone, thyroid hormone [usually] relieves the initial stimuli that caused the secretion of TRH and inhibits the release of TSH |
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Term
| What is the effect of thiocyanate on the thyroid gland and thyroid secretion? |
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Definition
| thiocyanate competitively inhibits the iodide pump, reducing iodide trapping; this causes reduced thyroid hormone production, which stimulates the anterior pituitary to produce more TSH, which causes hypertrophy and increased activity of the thyroid gland; eventually this can cause goiters |
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Term
| What ions have similar effects to thiocyanate? |
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Definition
| perchlorate and nitrate ions |
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Term
| What is the effect of propylthiouracil on the thyroid gland? |
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Definition
| propylthiouracil inhibits peroxidase and inhibits iodinated tyrosine from coupling to form thyroid hormone, which causes decreased thyroid hormone synthesis, which stimulates the anterior pituitary to secrete TSH, which stimulates hypertrophy and increased activity in the thyroid gland; eventually, this may result in goiters |
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Term
| What medications have similar effects to propylthiouracil? |
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Definition
| methimazole and carbimazole |
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Term
| What effect does the administration of inorganic iodide have on the thyroid gland? Why would it be administered in high doses? |
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Definition
| In high doses, inorganic iodide will reduce or stop iodide trapping and paralyze endocytosis of colloid, inhibiting thyroid hormone release and reducing the activities of the thyroid gland itself; this results in a decrease of its size and perfusion of the gland; it is sometimes administered in high doses a few weeks prior to thyroid surgery to reduce the bleeding and amount of surgery needed on the gland |
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Term
| Describe thyroid receptors. |
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Definition
| Mention: 1. often occur in heterodimers (often thyroid receptor and retinoic acid receptor (RAR), 2. receptors have a higher affinity for T3 than T4, 3. occurs in TR-alpha and TR-beta |
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Term
| Which has more binding in target tissues: T3 or T4? What happens to most T3 in the target tissues? What happens to most T4 in the target tissues? |
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Definition
| T3; most T3 binds to target tissue receptors; most T4 is converted to T3 by having an iodide removed by thyroid deiodinase |
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Term
|
Definition
| excessive thyroid hormone secretion |
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Term
| What are the symptoms of hyperthyroidism? |
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Definition
| increased body temperature, trembling from fine motor muscles, increased metabolic activity, bleeding problems in women, impotence in men, weight loss, possible psychosis, insomnia, protein catabolism, muscle weakness, nervousness, excitability, and exothalmos |
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Term
| What is exothalmos? What causes it? |
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Definition
| Exothalmos is the bulging of eyes that occurs with hyperthyroidism. It is caused by edematous swelling of the retro-orbital tissues and degeneration of extraocular muscles, causing protrusion of the eyeballs; depending on severity, eyelids may not close properly, the eyes may become infected, irritated, dry, or develop ulcers; if the protrusion is severe enough, the optic nerve may be stretched and there may be a loss of eyesight; the condition is often lessened by treatment for hyperthyroidism |
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Term
| What are the causes of hyperthyroidism? |
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Definition
| Toxic goiter, Graves' disease, or thyroid adenoma |
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Term
| What causes Graves' disease? |
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Definition
| an auto-immune condition in which immunoglobulins (TSIs) form that attack TSH receptors, causing a huge increase in thyroid stimulation; the TSIs are more competitive for TSH receptors than TSH itself and have a greater affinity for the receptors (TSIs stimulate for 12 hours while TSH only stimulates for 1 hour); negative feedback causes TSH levels to drop to almost zero |
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Term
| What is a thyroid adenoma? What does it do? |
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Definition
| a non-autoimmune condition involving a tumor growing in the thyroid gland; thyroid hormone secretion by the adenoma suppresses the secretion of TSH, so the gland itself will degenerate and not produce thyroid hormone |
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Term
| How is hyperthyroidism diagnosed? |
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Definition
| It is usually diagnosed with the measurement of free thyroid in the blood; other methods include the measurement of BMR (increase to +30 or +60 for severe hyperthyroidism), [TSH] radioimmunoassay measurement (almost zero), or [TSI] radioimmunoassay measurement (high in thyrotoxicosis and low in thyroid adenoma) |
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Term
| How does one treat hyperthyroidism? |
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Definition
| 1. surgical removal of part of the gland - the patient is usually put on propylthiouracil until BMR returns to normal, then the patient is given inorganic iodides to reduce the size of the gland prior to surgery, or 2. radioactive iodide treatment - patient is injected with 5 millicuries of radioactive iodide, which is almost entirely absorbed within 1 day; the patient is reassessed in a few weeks and given additional doses if needed or oral thyroxine to supplement if too much thyroid function is lost |
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Term
|
Definition
| an undersecretion of thyroid hormone |
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|
Term
| What are the symptoms for hypothyroidism? |
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Definition
| decreased BMR, lethargy, weight gain, sluggish motor response, possible bleeding problems in women, decreased libido in men and women, decreased hair growth, scaliness of the skin, decreased HR, decreased BV, decreased perfusion, constipation, husky voice, possibly atherosclerosis, and potentially myxedema |
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Term
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Definition
| A condition caused by an almost total lack of thyroid hormone in which the patient develops bagginess and swelling of the face and hyaluronic acid and chondroitin sulfate build up in the IF |
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Term
| How does hypothyroidism cause atherosclerosis? |
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Definition
| Because the thyroid hormone encourages the liver to clear cholesterol from the blood, a lack of thyroid hormone can cause increased blood cholesterol and deposition of the cholesterol in the arteries, causing atherosclerosis |
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|
Term
| What can cause hypothyroidism? |
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Definition
| Hashimoto's disease, endemic colloid goiter, idiopathic non-toxic colloid goiter, or destruction of the thyroid gland |
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Term
| What is Hashimoto's disease? What causes? |
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Definition
| Hashimoto's disease is an autoimmune disease in which immune system attacks the thyroid gland, causing thyroiditis, deterioration, fibrosis, and destruction of the gland; sometimes presents in family history and is often misdiagnosed as PMS or depression; patients have an initial increase in thyroid hormone, then have a loss of thyroid function due to cells dying |
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Term
| What is an endemic colloid goiter? What causes it? |
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Definition
| Endemic colloid goiter is a goiter caused by iodide deficiency; iodide deficiency causes a decrease in thyroid hormone production, which causes a stimulation of the pituitary gland to secrete TSH, which will cause hypertrophy and increase in activity of the thyroid gland, but without iodide no thyroid hormone will be produced; this results in a colloid goiter |
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Term
| What is an iodopathic non-toxic colloid goiter? What causes it? |
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Definition
| This occurs in patients with normal or low thyroid hormone levels; if I knew the cause, I'd be richer than I am, but the cause is unknown (hence idiopathic); mild thyroiditis suggests TSH may stimulate non-inflamed parts of the gland to grow while the inflamed parts do not produce thyroid hormone; some people have defects in the enzyme systems |
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Term
| What defects in enzyme systems may occur in an idiopathic non-toxic colloid goiter? |
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Definition
| Deficient iodide-trapping mechanism, deficient peroxidase system, deficient coupling of iodinated tyrosines, deficiency of deiodinase enzyme |
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|
Term
| Define goitrogenic. What foods are goitrogenic? |
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Definition
| Goitrogenic - causing goiters; turnips and cabbages are goitrogenic, behaving like propylthiouracil |
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Term
| How is hypothyroidism diagnosed? |
|
Definition
| Hypothyroidism presents with decreased thyroid hormone concentration accompanied with increased TSH concentration (except in cases involving pituitary dysfunction or a depressed response of the pituitary gland to TRH), and a decreased BMR |
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Term
| How is primary hypothyroidism treated? |
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Definition
| Primary hypothyroidism is treated with oral administration of thyroxine |
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