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PHYSIOLOGY II > Lecture 14: Thyroid Gland > Flashcards

Lecture 14: Thyroid Gland Flashcards

1
Q

Functional units of the thyroid gland, composed of sphered filled w/ colloid and surrounded by a single layer of follicular cells

A

follicule

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2
Q

what is Thyroglobulin (Tg)

A

glycoprotein rich in Tyrosine, the main component of colloid

a scaffold that harbors thyroid hormones at various stages of synthesis

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3
Q

major secretory cells at various stages of thyroid hormone synthesis, they surround follicles

A

Follicular cells

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4
Q

_______ cells that secrete calcitonin are also present in the thyroid gland and are important for Ca balance

A

C cells

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5
Q

composition of amine hormones (Thyronine, T4 and Triiodothyronine, T3)

A

amine hormones that are made from 2 tyrosine molecules w/ 3 (T3) or 4 (T4) iodine molecules

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6
Q

where are thyroid hormones stored

A

within the thyroid

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7
Q

what regulates thyroid gland function, growth and synthesis of T3/T4

A

HPT axis

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8
Q

what does Thyrotropin-releasing hormone (TRH) from the hypothalamus stimulate the release of

A

TRH stimulates the release of thyroid-stimulating hormone (TSH) from pituitary thyrotropes

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9
Q

where is thyroid stimulating hormone (TSH) released from

A

pituitary thyrotropes

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10
Q

what stimulates the release of thyroid hormone, T3 + T4

A

Thyroid-stimulating hormone (TSH)

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11
Q

Regulation of thyroid hormones requires the dietary intake of…..?

A

iodine

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12
Q

The HPT axis is regulated by ________ and stress and cold

A

diurnal rhythm

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13
Q

where does negative feedback of thyroid hormone occur

A

at the hypothalamus and anterior pituitary

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14
Q

is there more T3 or T4 circulating

A

T4

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15
Q

_______ has rapid action and degradation whereas ______ is slow to response

A

T3 fast
T4 slow

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16
Q

what thyroid hormone has 10x more binding affinity than the other?

A

T3
T4 is slow to bind to receptors

17
Q

what thyroid hormone is the blood transport form and what one is the signaling form

A

blood transport = T4
signaling form = T3

18
Q

what are the steps of thyroid hormone synthesis?

A
  1. starts w/ tyrosine precursor
  2. iodines are attached to the tyrosine to create either: Monoiodothyrosine (MIT) or diiodothyrosine (DIT)
  3. coupling reaction to create T3 or T4
    MIT + DIT = T3
    DIT + DIT = T4
  4. T3 and T4 are attached to a thyroglobulin (Tg) backbone and stored in colloid
19
Q

where is Thyroglobulin (Tg) synthesized

A

in follicle cells
then exocytosed to colloid

20
Q

what is the only known role for Iodide in the body

A

synthesis of T3/T4

21
Q

where is iodide found in the body

A

ALL of it is within the thyroid

22
Q

complexed iodide is oxidized to active iodide by what enzyme

A

Thyroperoxidase (TPO)

23
Q

Tyrosine iodination occurs in the ______

A

colloid
iodides in the collide are attached by TPO to tyrosine molecules within the Tg molecules

24
Q

why is there more T4 than T3?

A

the coupling rxn to form T4 is 10x faster than making T3

25
Tg-Thyroid hormone complex is taken into the follicular cell via _______
phagocytosis
26
what are the 3 main binding proteins for thyroid hormones
Thyroid Binding Globulin (binds 75% of T3/T4) Transthyretin (TTR) binds 10% of T4 * secreted into CSF to allows transport to NS Albumin binds 15% T4, 25% T3 only 1% free
27
what are the half lives of T3 and T4
T3: 1 day T4: 7 days T4 half life probably longer b/c it has higher binding affinity
28
what fraction of thyroid hormone is important for signaling and HPT feedback
the 1% that is free
29
what fraction of thyroid hormone allows for a serum reserve capacity?
the bound hormones
30
how is T4 converted into T3
tissue **deiodinase**cleaves Iodine groups ~80% of T4 is converted into T3
31
what are the 3 types of deiodinases and where can they be found
**type 1** in liver, kidney, thyroid **type 2** in brain, pituitary, brown fat, yhyroid, placenta, striated muscles **type 3** in brain, placenta, skin
32
Deiodinase II _______ thyroid signaling whereas Deiodinase ______ thyroid signaling
II -promotes III - inhibits
33
what form of T3 is non-functional
reverse T3 (rT3)
34
why are T3/T4 released slowly to tissue cells
b/c of their high binding affinities for plasma proteins
35
the main effect of thyroid hormone is to....
regulate metabolic rate
36
what explains an elevated body temp in hyperthyroidism
increased metabolism
37
what causes goiters
increases TSH causes growth of the thyroid gland (hypothyroidism)
38
name three causes of **hypothyroidism**
* primary failure of thyroid gland * anterior pituitary deficiency * iodine deficiency
39
name three causes of **hyperthyroidism**
* thyroid stimulating immunoglobulin (Grave's disease) * excessive pituitary function * hypersecreting thyroid tumor

PHYSIOLOGY II (17 decks)

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