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26 Cards in this Set
- Front
- Back
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What is the name of the anatomy that connects the two lobes of the thyroid?
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The isthmus
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What is the weight range for the thyroid given goiter?
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20g to 100g
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What are two types of innervation to the thyroid?
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Cholinergic and adrenergic innervation
Mostly vasomotor. Controls blood flow. |
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What is the blood flow rate through the thyroid?
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6ml/min, higher than the kidney
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What are the two morphologies of the thyroid cells?
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Inactive = flat epithelial cells
Active = cuboidal epithelial cells endocytocizes colloid surrounded by capillary plexus and parafollicular cells. |
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What is colloid? How is it taken up?
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What thyroid cells are full of. Colloid is where thyroid hormones are made and stored.
Apical side of epithelial cells have microvilli and pseudopodia to take up colloid when active and produce thyroid hormone. |
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How is thyroid hormone synthesized?
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- made from iodide and tyrosine
- tyrosine is iodonated - MIT iodonated at the 3 position - DIT iodonated at the 5 position Condensation/coupling rxn: MIT + DIT --> T3 DIT + DIT --> T4 (90%, precursor for T3) requires thyroid peroxidase |
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What is iodine trapping?
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Iodine is taken up by follicular cells against its gradient (30:1). It must use active transport by NIS Na antiport, NA/K ATPase assists. Transporter newly identified as PENDRIN.
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How much iodine do we need and store?
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Need 1 mg / week, the thyroid stores about 8g, or 3 months worth
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What is THYROGLOBULIN and what does it do?
What important enzyme does TG store? |
Large GLYCOPROTEIN attached to T3 and T4 to transfer during endocytosis.
MIT, DIT, T3 and T4 are made on it, and the whole TG is stored in the colloid. Ratio: MIT (7) : DIT (6) : T4 (2) : T3 (0.2) per thyroglobulin thyroid peroxidase, which needs H2O2 to iodonate MIT and DIT. |
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What happens during Thyroid Hormone secretion?
What is the name of the initial receptor? |
- TSH attaches to a membrane receptor, and signals release through cAMP.
- microvilli do pinocytosis of colloid droplets - colloid fuses with lysozome, proteolysis, cleavage of T3, T4, MIT and DIT - T3 and T4 diffuse out of the cell into circulation - DIT and MIT are deiodonated and iodine recycled. THYROTROPIN |
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What inhibits thyroid hormone secretion?
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lithium and high dose iodine.
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What 3 binding proteins serve as a reservoir for thyroid hormone?
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Thyroxine Binding Globulin (TBG): has 20x higher affinity for T4 than T3
Transethyretin (TTR): Albumin: low affinity |
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What is the production and storage rate of T4 (useless version) versus T3?
Why do we have so much T4?? |
Thyroid makes 5x more T4 than T3 per day, so you do peripheral conversation to T3.
Binding proteins have a higher affinity for T4, and T4 has a one week half life instead of a day like T3 does. |
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What happens to TSH levels and plasma T4 and T3 levels in Hyperthyroid and Hypothyroid states?
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HYPER: low TSH, high T4 and T3
HYPO: High TSH, low T4 and T3 overactive thyroid is putting out more T4/T3!! |
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How do you measure thyroid activity in the clinical setting?
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T3 Resin Uptake is inversely proportional to the # of unoccupied binding sites in Thyroid Hormone Binding Proteins, and proportional to the # of OCCUPIED binding sites.
so basically, the T3RU that couldn't find a free area to bind is inversely proportional to the occupied sites, and you can assay that quantity and determine how much is bound. |
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How is thyroid hormone (T3/T4) used/taken up?
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T4 is peripherally converted/deiodonated in the liver, kidney, muscle and other target tissues. It is converted to T3 or rT3 (inactive).
enzyme: deiodonase In a target cell, T4 converts to T3, binds TR nuclear receptor, TR deterodimerizes with RXR binds DNA at thyroid response element and regulates gene transcription. |
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What happens to T3/T4 levels when you starve?
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T3/rT3 rapidly decrease, T4 doesn't really change. you get cold (metaphorically)
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List some major Thyroid Hormone actions
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- bone and skeletal muscle growth
- tooth development - skin and hair - neural axon branching, myelination - alertness, reflexes - increases O2 use and basal metabolic rate <-- IMPORTANT - increase Na/K ATPase, oxidative phosphorylation - increased ventilation, cardiac output - promote insulin action - build and break down protein depending on T3 concentration - low: break down fat. high: decrease cholesterol. - increase K+, nitrogen, urea. |
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How does TSH regulate the thyroid? What happens if you have sustained TSH release?
What negatively feeds back on TSH? |
through cAMP, increases iodine uptake, peroxidase activity, pinocytosis of colloid, release of T4/T3, TG production
basically everything that is conducive to production and release of T3/T4. Sustained TSH = hypertrophy and hyperplasia / GOITER negative feedback = T3 |
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What are the effects of all of the following on TSH?
iodine estrogen cold temp stress, dopamine, somatostatin, fasting drugs: perclorate, thiocyannate, thiocarbamides |
iodine: low (increase TSH), high (decrease TSH)
estrogen: increase TSH cold temp: increase TSH stress, dopamine, somatostatin, fasting: DECREASE TSH drugs: perclorate, thiocyannate, thiocarbamides: DECREASE iodine uptake and organification. |
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hyperthyroidism / graves' disease
1) what is LATs? |
Long Acting Thyroid Stimulator, antibody that binds and activates TSH-R (autoimmune disease).
you can also have a pituitary tumor that oversecretes TSH, or ectopic thyroid tissue tumor, or injection of T3/T4. |
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What are the symptoms of hyperthyroidism?
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goiter (increased TSH-R activity)
heat metabolic (sweat, weight loss, hunger) tachycardia, atrial fibrillation diarrhea moist skin, hair loss insomnia, hyperreflexia muscle weakness amenhorrhea retracted eyelids, protrusion |
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Tx for hyperthyroidism
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high dose iodine
thiocarbamides beta blockers surgery radioactive iodine |
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What is Hashimoto's disease?
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chronic thyroiditis/HYPOthyroidism
autoimmune destruction of the thyroid iodine deficiency hashimoto shows up in a baby as a HUGE inflamed thyroid glands. |
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Hypothyroidism symptoms
Tx? |
myxedema: dermal edema
goiter if TSH increases metabolic cold intolerance, weight GAIN, decreased appetite bradycardia constipation dry, yellow skin, coarse hair, eyebrows edema lethargy, fatigue, slow reflexes common in children, cretinism, mental retardation, dwarfed can result from congenital DEFECT IN IODINE TRAPPING, peroxidase, deiodinase Tx: thyroid hormone, careful, don't induce HYPERthyroidism! |
