Lecture & Vodcast 2 -- Exam 5 Flashcards by Camille Miceli

What occurs in the follicle of the thyroid gland?

thyroid hormone (TH) production

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What is so special about the way thyroid hormone is synthesized?

only hormone synthesized extracellularly

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What is colloid in the thyroid gland?

thick liquid where thyroid hormone is made

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What is the precursor molecule for thyroid hormone?

tyrosine

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When synthesizing thyroid hormone, tyrosine is converted into ____ and _____

MIT
DIT

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What is the difference between the intermediate of thyroid hormones MIT and DIT?

MIT: C3 iodide
DIT: C3 & C5 iodide

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The combination of DIT + DIT results in the formation of ….

T4 (inactive)

most common in blood

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The combination of MIT + DIT results in the formation of ….

T3 (active form)

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What enzyme converts T4 into the active T3?

5’ deiodinase (removes 5’ iodine)

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What enzyme converts T4 into the reverse T3?

type III deiodinase

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What are the 7 steps of thyroid hormone synthesis?

iodide trapping
thyroglobulin synthesis
iodination
coupling
endocytosis
proteolysis
secretion/recycling

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What occurs during step 1 of thyroid hormone synthesis, iodide trapping?

Na/I symporter brings Na and iodide into cell

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What occurs during step 2 of thyroid hormone synthesis, thyroglobulin synthesis?

thyroglobulin is made which is the source of tyrosine for later steps

** inside cell

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What occurs during step 3 of thyroid hormone synthesis, iodination?

iodide is converted into iodine which combines with tyrosine

** apical side of cell

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What occurs during step 4 of thyroid hormone synthesis, coupling?

MIT + DIT = T3
DIT + DIT = T4

** apical side of cell

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What occurs during step 5 of thyroid hormone synthesis, endocytosis?

T4 / T3 is brought back inside cell to be recycled or stored to be secreted

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What is the hypothalamic pituitary thyroid axis?

hypothalamus: TRH
pituitary: thyrotrophs sense TRH and release TSH
thyroid: TSH induces production and release of T4 and T3

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Does somatostatin and dopamine __increase/decrease___ the release of TSH?

decrease

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If you have just eaten what is the affect on TSH secretion?

increase (wants to increase metabolism)

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If you are stuck in the snow for 12 hours what is the affect on TSH secretion?

decrease (wants to slow metabolism and preserve energy)

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___ can directly AND indirectly negatively feedback to prevent TRH and TSH secretion

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What is the thyroid hormones primary role?

increase metabolism (increases after eating)

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In primary hyperthyroidism, what is the affect on levels of T4, T3, and TSH

T3 & T4: increase
TSH: decrease

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What is Graves disease?

autoantibodies that activate TSH receptor on thyroid causing increased T4 and T3 secretion

** hyperthyroidism

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Does hyperthyroidism cause increased or decreased weight?

decreased (increased metabolism)

Why does hyperthyroidism cause a goiter?

thyroid gland swells due to constant stimulation of TSH by auto-Ab causing increased thyroid follicles size

In primary hypothyroidism, what is the affect on levels of T4, T3, and TSH?

T3 & T4: decrease TSH: increase

Why does TSH levels increase in hypothyroidism?

no negative feedback due to lack of T3 and T4 so pituitary keeps making TSH

What is Hashimoto's disease?

autoantibodies destroy thyroid follicles * hypothyroidism

Does hypothyroidism cause increased or decreased weight?

increase (decreased metabolism due to underactive thyroid)

Why does hypothyroidism cause decreased heart rate (bradycardia)?

decreased sympathetic activity

Why do babies with hypothyroidism have decreased growth and cognitive issues?

thyroid hormone is important in growth and brain development

Hypercalcemia causes _________ nerve excitability

decreased

Hypocalcemia causes _________ nerve excitability

increased

Does hypo or hyper-calcemia cause tetany (spasms)?

hypocalcemia (increased nerve excitability)

What 3 places regulate Ca2+ balance?

gut, bones, kidneys

Osteoblasts or osteoclasts contain receptors for PTH, Vitamin D3 and estrogen.

osteoblasts (build bone)

Osteoblasts or osteoclasts contain receptors for calcitonin.

osteoclasts (breaks down bone)

What cells break down bone?

osteoclasts

What cells build bone?

osteoblasts

What are the 2 sources of vitamin D?

milk and sun

What is the role of Vitamin D in regards to calcium?

* regulates Ca2+ levels stimulates formation of calbindin to remove Ca2+ out of cell

Vitamin D3 is converted into ___________ in the liver which is a intermediate for active vitamin D

25-OH-vitaminD3

What are the 2 forms of vitamin D made from 25-OH-vitamin D3?

1,25-OH- vitamin D3 24,25-OH- vitamin D3

Is 1,25-OH- vitamin D3 or 24,25-OH- vitamin D3 the active form of vitamin D?

1,25-OH- vitamin D3

When 1-alpha-hydroxlase acts on 25-OH-vitaminD3, what form of vitamin D made?

1,25-OH- vitamin D3 ** active form

When 24-alpha-hydroxlase acts on 25-OH-vitaminD3, what form of vitamin D made?

24,25-OH- vitamin D3 ** inactive form

Where are 1,25-OH- vitamin D3 24,25-OH- vitamin D3 located?

kidney

Hypocalcemia causes 1,25-OH- vitamin D3 or 24,25-OH- vitamin D3 to be made.

1,25-OH- vitamin D3

Hypocalcemia ___________ secretion of PTH

increases

Increased PTH secretion causes 1,25-OH- vitamin D3 or 24,25-OH- vitamin D3 to be made.

1,25-OH- vitamin D3

Low phosphate causes 1,25-OH- vitamin D3 or 24,25-OH- vitamin D3 to be made.

1,25-OH- vitamin D3

High 1,25-OH- vitamin D3 causes 1,25-OH- vitamin D3 or 24,25-OH- vitamin D3 to be made.

24,25-OH- vitamin D3 ** too much 1,25 causes negative feedback on itself

vitamin D bind to receptor in gut which causes the production of _________

calbindin

What is the role of calbindin in the small intestine?

carrier Ca2+ out of cell so it can be taken into blood stream

In the intestines do Ca2+ and phosphate follow the same direction or go in opposite directions?

same direction

What is the role of chief cells in the parathyroid gland?

secrete parathyroid hormone in response to Ca2+ levels ** Ca2+ sensors

What is the role of oxyphil cells in the parathyroid gland?

provides structural integrity

Does high or low Ca2+ levels inhibit PTH secretion?

high

What is the caveat involving chief cell's Gq receptor?

the release of intracellular calcium actually inhibits release of PTH

What is the role of the parathyroid hormone?

raises Ca2+ levels in blood

In the kidneys do Ca2+ and phosphate follow the same direction or go in opposite directions and why?

opposite there would be too much salt and would cause kidney stones

hypocalcemia causes __increased/decreased__ PTH secretion which causes increased ___1-alpha-hydoxylase / 24-alpha-hydroxylase___ activity which results in ___1,25-OH- vitamin D3 or 24,25-OH- vitamin D3___ to be made causing ___increased/decreased___ Ca2+ reabsorption from the GI

increased 1-alpha-hydoxylase 1,25-OH- vitamin D3 increased

Osteoclasts break down bone under the stimulation of _____ in order to release Ca2+ to increase its levels in the blood

PTH * done indirectly

How does PTH indirectly stimulate osteoclasts to breakdown bone to release ca2+?

osteoBLASTS have PTH receptors; when PTH binds to osteoBLASTS it releases cytokines to stimulate osteoCLASTS

What is estrogen's effect on osteoblasts?

limits its ability to produce cytokines to activate osteoclasts (why in menopause decreased estrogen causes bone damage)

PTH causes __________ plasma Ca2+ and ________ plasma phosphate

increase decrease

What is the role of calcitonin?

decreases Ca2+ levels and increases phosphate levls ** opposes PTH

What cell produces calcitonin?

C-cells

How does calcitonin decrease Ca2+ levels?

binds to osteoclasts to prevent their function

Vitamin D deficiency results in _____calcemia

hypocalcemia (decreased GI reabsorption b/c no calbindin produces to move Ca2+ out of GI cells)

In hyperparathyroidism, what is the effect on PTH, Ca2+ and PO4- levels?

increased PTH increased Ca2+ decreased PO4 (elevated Ca2+ is not feeding back to decrease PTH)

Increased calcium can lead to kidney _________

stones

increased PTH leads to what effect on bones?

increased degradation (due to trying to increase Ca2+ levels)

Elevated calcium not caused by hyperparathyroidism is a result of ______

PTHrP (tumor of the parthyroid gland)

PTHrP binds to osteo______ similar to PTH causing their activation

osteoBLASTS (go on to activate osteoclasts via cytokines)

Why does PTHrP cause a vicious cycle?

it causes release of Ca2+ from bones but that Ca2+ can feed the cancer

PTHrP can also bind to PTH receptor in kidneys to stimulate Ca2+ _________ and phosphate _________

Ca2+ reabsorption = hypercalcemia phosphate secretion