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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
Q

Tg-Thyroid hormone complex is taken into the follicular cell via _______

A

phagocytosis

26
Q

what are the 3 main binding proteins for thyroid hormones

A

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
Q

what are the half lives of T3 and T4

A

T3: 1 day
T4: 7 days

T4 half life probably longer b/c it has higher binding affinity

28
Q

what fraction of thyroid hormone is important for signaling and HPT feedback

A

the 1% that is free

29
Q

what fraction of thyroid hormone allows for a serum reserve capacity?

A

the bound hormones

30
Q

how is T4 converted into T3

A

tissue deiodinasecleaves Iodine groups
~80% of T4 is converted into T3

31
Q

what are the 3 types of deiodinases and where can they be found

A

type 1 in liver, kidney, thyroid
type 2 in brain, pituitary, brown fat, yhyroid, placenta, striated muscles
type 3 in brain, placenta, skin

32
Q

Deiodinase II _______ thyroid signaling whereas Deiodinase ______ thyroid signaling

A

II -promotes
III - inhibits

33
Q

what form of T3 is non-functional

A

reverse T3 (rT3)

34
Q

why are T3/T4 released slowly to tissue cells

A

b/c of their high binding affinities for plasma proteins

35
Q

the main effect of thyroid hormone is to….

A

regulate metabolic rate

36
Q

what explains an elevated body temp in hyperthyroidism

A

increased metabolism

37
Q

what causes goiters

A

increases TSH causes growth of the thyroid gland
(hypothyroidism)

38
Q

name three causes of hypothyroidism

A
  • primary failure of thyroid gland
  • anterior pituitary deficiency
  • iodine deficiency
39
Q

name three causes of hyperthyroidism

A
  • thyroid stimulating immunoglobulin (Grave’s disease)
  • excessive pituitary function
  • hypersecreting thyroid tumor

PHYSIOLOGY II (17 decks)

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