Glossary of Thyroid gland
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- What is the basic structure of the thyroid gland?
- -2 lobes, seperated by an isthmus.
-Supplied with lots of blood.
-SNS and PNS innervation
- What are the main functional units of the thyroid?
- How are Thyroid follicles organized?
- 1. Follicular cells at periphery, w/ tight junctions between.
2. Filled with colloid
3. Surrounded by capillaries
4. Parafollicular cells btwn.
- What is colloid?
- The main ingredient in follicles; thick/gelatinous; composed of 10-25% thryoglobulin.
- what is Thyroglobulin?
- the storage form of thyroid hormones - 10-25% of colloid, so the thyroids possess their hormone in largely stored amts.
- What are Parafollicular cells?
- cells that secrete calcitonin
- What is the main stimulus for release of TRH from the hypothalamus?
- Cold temps
- what two hormones of the hypothalamus affect thyrotrophs?
What are thyrotrophs?
- 2 hormones: TRH and somatostatin
Thryotrophs are the cells that secrete thyroid STIMULATING hormone in the PITUITARY.
- how does thyroid stimulating hormone effect the thyroid follicles?
- It increases their size, number, and function.
- and what is the function of thyroid follicles?
- To produce thyroid hormones.
- How does thyroid hormone feedback on the hypothalamus?
How does TH effect Thyrotrophs?
- -Inhibits TRH
(both from hypothal)
-Inhibits TSH from pituitary
- What is another name for TSH?
- what ARE thyroid hormones, structurally?
- Iodinated derivitives of Tyrosine (an amino acid).
- Therefore, what does synthesis of TH rely on?
- Iodine in diet - iodized salt
- What two precursors are Thyroid hormones formed from?
What 2 THs are formed?
- MIT and DIT. Each then forms T3 and T4 resp.
- What are the ratios of T3 and T4 formed, which is more potent?
- T3 is about 1-2% of TH in plasma; T4 is 98-99%; T3 is way more potent so you need less.
- How is Iodide taken up by thyroid follicle cells from ECF?
- -By active transport (ATP depnd)
-Used to synthesize Thyroglobulin
- What occurs at junction between follicular cells and the colloid space within the Thyroid gland?
- Tyr amino acids get iodinated inside Thyroglobulin, then form T3 or T4 inside the colloid lumen. Catalyzed by TPO enzyme.
- Where are T3 and T4 stored until needed by the body?
- In the lumen of the follicle - where colloid is.
- How do the thyroid hormones get out of the follicles when needed by the body?
- Taken out of lumen by endocytosis into the follicle cells, then lysosomes break down Thyroglobulin into amino acids and T3/T4. They diffuse into capillaries around thyroid.
- Knowing the process of making T3 and T4, how does TSH affect TH synthesis and secretion?
- By upregulating the enzymes that catalyze the processes, increasing Iodide uptake, Thyroglobulin synthesis, Tyr iodination, endocytosis, and Increasing thyroid follicle cell size tremendously!
- why is TSH synthesis and secretion so complex?
- because TH can't be stored in vesicles due to being hydrophob. This gives a mechanism for storing a reserve when iodine is unavailable.
- what carries thyroid hormone in the SERUM? where is it synthesized?
- Thyroxine binding globulin
-Synthesized in the liver.
- what are the 3 plasma proteins for transfer of thyroid hormone?
- -Thyroxine binding globulin 80%
- Is there typically more bound or free thyroid hormone in plasma?
- Bound - 99%; only 1% is free.
- What is the purpose of Thyroid binding globulin?
- It buffers the free thyroid hormone in our blood; prevents it from getting degraded too fast. If we don't need it, it's bound; if we do, it's let loose.
- What is the primary effect that thyroid hormone has on cells?
- It changes gene expression.
- What form of thyroid hormone is the active form in tissues?
- So how is T4 converted to T3?
- by removal of iodine, by action of 5'-Deiodinase.
- How is T4 converted in the
-Thyroid, liver, kidneys?
- Brain: cells take up T4 and deiodinate in the cytoplasm.
Other: use 5'deiodinase to convert T4 to T3
- How is T3 inactivated?
- with 5-deiodinase
It generates reverse T3, which is inactive, as opposed to normal T3 which is active.
- What are the 3 main functions of Thyroid hormones?
- 1. CNS development
3. Basal metabolic rate regulation
- When does thyroid hormone affect CNS development
- IN the 3rd trimester to the 1st year of life.
- How does TH affect growth?
- -Increases GH synthesis
-Increases synthesis of structural and metabolic proteins in heart/muscle/liver.
- How does TH affect the basal metabolic rate?
- -Controls enzyme production;
-Incr. oxidative phosphorylation
-Incr. Heat production
- What are 3 types of Hypothyroidism?
- 1. Cretinism
- What are Cretinism symptoms?
- -Mental retardation due to impaired CNS
-Decreased body size
- What is a Goiter?
- An enlarged thyroid
- What causes a goiter?
- High levels of TSH - they increse follicle size signific!
-But you have low T3/T4 levels.
- What are symptoms of "Myxedema"?
Can't stand cold temps
Bradycardia, edema in face. Droopy looking
- What causes hypothyroidism?
- Low iodine in the diet.
- What is Hashimoto's disease?
- An autoimmune destruction of the thyroid.
- What are 2 categories of Hyperthyroidism?
- 1. Thyrotoxicosis - high TH levels from any source
2. Hyperthyroidism - just high TH levels from the gland.
- What are symptoms of hyperthyroidism?
- -Shaky, Nervous, fast heart rate, STARING, insomnia
- Can a goiter be caused by hyperthyroidism?
- Yes - from toxic T3 and T4 levels.
- What type of goiter is associated with toxic levels of T3 and T4?
- What are 2 causes of hyperthyroidism?
- 1. Grave's disease
2. Hamburger thyrotoxicosis
- What is grave's disease?
- An autoimmune disease where Ab stimulates TSH receptors on the follicle cells - the major cause of most hyperthyrodoism.
- What is hamburger thyrotoxicosis?
- When you ingest thyroid tissue i n improperly butchered meat (GROSS!)
- What's the major difference between Hashimoto's and Grave's disease?
- Both are autoimmune, but in Hashimoto, antibody destroys thyroid tissue and suppresses.
Graves, Antibody mimics TSH and binds its receptor.
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