Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
57 Cards in this Set
- Front
- Back
|
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?
|
Follicles
|
|
|
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
-Stimulates Somatostatin (both from hypothal) -Inhibits TSH from pituitary |
|
|
What is another name for TSH?
|
Thyrotropin
|
|
|
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 is Thyroglobulin?
|
A precursor of thyroid hormone; very large globular protein with lots of tyrosines.
|
|
|
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%
-Albumin 10% -Transthyretin 10% |
|
|
Is there typically more bound or free thyroid hormone in plasma?
|
Bound - 99%; only 1% is free.
|
|
|
finish
|
ok
|
|
|
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?
|
T3
|
|
|
So how is T4 converted to T3?
|
by removal of iodine, by action of 5'-Deiodinase.
|
|
|
How is T4 converted in the
-Brain? -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
***(NOT 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
2. Growth 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
2. Goiter 3. Myxedema |
|
|
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"?
|
Fatigue/lethargic
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?
|
Hyperthyroidism
|
|
|
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. |
|
|
What type of goiter is associated with toxic levels of T3 and T4?
|
Hyperthyroidism
|
|
|
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. |
