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Flashcards in Thyroid gland Deck (92)
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1

Where is thyroid gland found and is its blood supply

located below larynx

Large blood supple and innervated with sympathetic nerves

2

What is the functional unit of thyroid gland

Thyroid follicles

3

what is found in thyroid follicle

a single layer of epithelial cells surrounding a lumen that contains colloid ( few 100 follicles per gland)

and parafollicular cells

4

What is colloid made from

 thyroglobullin in the collide 

5

What is present on the apical surface of the thyroid follicle

Cilia

6

The other name for parafollicular cells and what they are source of

C-cells

Calcitonin

7

Function of thyroid gland

Function: to secrete
the quantity of
thyroid hormone to
meet the demand of
peripheral tissues

8

How the secretion of thyroid hormone is regulated

  • The blood flow regulates the thyroid hormones release by affecting the the delivery of TSH, iodine and nutrients
  •  Postganglionic sympathetic nerves control the blood flow through the gland

9

How c-cell can be found within thyroid gland

Associated with thyroid cell or outside the follicle

10

What is the structure of the cell when it is inactive and when overreactive

inactive-cuboidal

very active- columnar

11

T4 and T3 are made of (AA)

Iodinated tyrosine

Mono or diiodotyrosine

Tyrosine can take up up to 2 I per ring

12

structure of T3 and T4 and what positions I

T4- thyroxine, 2 diiodotyrosines together

T3: 3,5,3' triiodothyronine, 1 mono and 1 diiodotyrosine

13

to what forms peropheral tissues convert T3 and T4

14

Describe synthesis of T3 and T4

Na/K ATPase creates a gradient of Na (low inside the follicle)

  1. NIS: 2Na and 1I are brought into the cell(symporter) due to gradient of Na
  2. PDS: a trasnporter that transfers I from the follicle into the colloidal
  3. Meanwile: TSHR (receptor of TSH),which functions through GPCR and IP3/Ca system induces transcription and trasnfer of thyroglobulin(Tg) into the colloidal
  4. Ca in the cytoplasm induces production of H2O2 into the colloidal by taking H from NADPH 
  5. Thyroid peroxidase with H2O2 puts I on Tg in the colloidal
  6. Now Tg have T3,T4 and precursors
  7. Iodinated Tg is taken inside the follicle and undergoes hydrolysis
  8. mono and diiodotyrosine are recycles and I is given off to colloid again
  9. T4 and T3 is transported into the circulation. Not sure what transporter, but the candidate is MCAT10

15

What 3 parts are essential for thyroid hormone synthesis in thyroid gland

NIS (Na+/I- symporter),
TG (thyroglobulin), TPO (thyroid peroxidase)

16

how thyroid feedback works

17

What is trapping? what is organification? what is coupling?

1) active transport of iodine into the thyroid
cell (“trapping”)
2) oxidation of iodide and iodination of
tyrosyl residues in thyroglobulin
(organification)
3) linking pairs of iodotyrosines in
thyroglobulin to form T3 and T4
(coupling)

18

Is T3 or T4 more bioactive?

T3

19

What other organ apart from thyroid gland cna trap I

Salivary gland

20

What can block NIS and how this is used for treatment?

Anions (such as ClO4-) block uptake of iodine; perchlorate
can be used to block hyperthyroidism (also environmental
inhibitor of thyroid

21

Radioactive iodine is used for

Radioactive iodine (oral I131) can be used to destroy
thyroid tissue (in case of cancer or hyperthyroidism)

22

What is the structure of Tg

Dimer
contains about 140 tyrosines

23

What are psot translational modifications of Tg

v Extensively glycosylated in the Golgi (10% carbohydrate
by weight)
v Packaged into vesicles, exocytosed into the lumen of the
follicle

24

how iodination of Tg occurs

Thyroperoxidase is Packaged in an inactive form together with thyroglobulin (Tg) into vesicles in the Golgi
v Activated at the apical membrane by co-factors

25

Drugs inhibiting iodination are targeted on

Thyroperoxidase is the target for many drugs to reduce
thyroid hormone production e.g. thiocarbamide
inhibitors

26

Name of compounds that block thyroperoxidase and where they are found

and the result of blockage

Several inhibiting compounds (goitrogens) are present in
food (e.g. milk from cows fed certain plants, brassicae).


v Block of iodination results in increased TSH production,
resulting eventually in hyperplasia and goiter

27

What tyrosines become iodinated

Only the tyrosines on the surface of the Tg become
iodinated (about 1/3rd)

28

What stimulates coupling of MIT and DIT

TPO 

29

How much of T3 and T4 is in 1 Tg

  • Maximum of four T3 and/or T4 hormones within each Tg molecule are formed.
  •  The kinetics is such that it keeps the level of T3 (the active form of the thyroid hormones) steady despite fluctuations in the dietary intake of iodine.

30

Why thyroid gland have cilia

For endocytic mechanism for uptake of iodinated Tg