Thyroid Physiology Flashcards Preview

Endocrinology > Thyroid Physiology > Flashcards

Flashcards in Thyroid Physiology Deck (46):
1

Thyroid means

shield

2

What are two clinical properties that distinguish the thyroid gland from the other endocrine glands?

- Can be seen and palpated during routine physical.
- Has a trace element, iodine

3

Microscopic stucture of thyroid gland

Follicular cells surrounding Colloid in circular patterns. In between layers of follicular cells you have parafollicular cells.

4

What does Colloid contain

Thyroglobulin

5

What do parafollicular cells generate

calcitonin

6

The six steps of thyroid hormone synthesis

1) Iodide uptake by Na/I symporter
2) Thyroblobulin synthesis and release into the follicular lumen
3) Iodination of tyrosine residues in thyroglobulin
4) Endocytosis of iodinated thyroglobulin into follicular cells
5) Generatin and secretion of T3 and T4
6)Iodide recycling

7

Iodide is present in most of our food

true

8

Iodide travels from the gut into the bloodstream, through the bloodstream to the thyroid gland and comes into the follicular cells of the thyroid gland through what?

Na-Iodide symporter on the basolateral side of the cell (the side facing the blood vessel)

9

What can inhibit the uptake of iodide?

CIO4, TcO, SCN....I dont know what any of that is

10

What carries iodide from the apical side of the follicular cell into the colloid lumen?

Pendrin

11

THyroglobulin is made where?

In the Colloid

12

What is the surface of the colloid layer coated in>

Thyroid Peroxidase

13

What is the purpose of thyroid peroxidase

oxidizes iodide to iodine

14

Iodine then does what to thyroglobulin

reacts with the tyrosine residues to "iodinate them"

15

Internal rearrangement of two iodinate tyrosyl residues results in

Iosothyronine. This is catalyzed by thyroid peroxidase

16

As long as T3 and T4 are attached to the thyroglobulin backbone,

they are inactive

17

At the appropriate time, a droplet of colloid is endocytosed into the follicular cell

ok

18

This endocytosed colloid fuses with what

a native lysosome forming a lysoendosome

19

What happens inside the lysoendosome

Enzymes inside the lyso-endosome hydrolyze the tyrosine residues and you get active T3 and T4....THIS IS BIG

T3 and T4 get released into the blood

20

Iodide is recycled?

Yes

21

90% of what is released into the bloodstream is

T4, 10% T3....KNOW THIS

22

Once in the bloodstream, the thyroid hormones are immediately bound by

Plasma proteins like albumin or thyroid binding globulin (most attached to this)

23

What kinds of things decrease the amount of Thyroid Binding Hormone TBG?

Steroid Use

24

What kinds of things increase the amount of TBG?

Pregnancy, heroin use

25

Which is more active, T3 or T4?

T3

26

What must you have in the inner ring of thyroid hormone for it to be considered active?

Two iodines

27

The lack of iodine in the inner ring of what type of T3 molecule makes it inactive

Reverse T3

28

What is the enzyme responsible for the conversion of T4 to T3

5/3- Deiodinase

29

What are the two types of 5/3-Deiodinase?

Type 1 and type 2

30

Type 1 deiodinase is found where?

Liver, Kidney, Thyroid

31

Type 2 deiodinase is found where?

Pituitary, CNS, Placenta

32

Which Deiodinase is mainly responsible for the amount of free T3 found in the blood?

Type 1

33

Thyroid hormone is a peptide

KNOW

34

All peptide hormones have what type of Receptor? EXCEPT THYROID

ALL have a plasma membrane receptor except thyroid

35

Thyroid hormone has what type of receptor

nuclear

36

Thyroid hormone receptor (THR) forms a dimer with Retinoid X Receptor (RXR) and does what

Acts directly on the DNA to regulate transcription

37

Why does hyperthyroidism (physiologically) increase metabolism

Directly increases oxygen consumption and when oxygen consumption goes up, the amount of heat generated by the cells goes up

38

Increases in TRH lead to increases in TSH

truth

39

TRH acts on what cells where

Thyrotrophs in the anterior pituitary...generates the secretion and release of TSH

40

How are TRH and TSH levels controlled

Feedback mechanism involving T4 and T3. As free T4 and T3 levels rise, TRH goes down via direct and indirect mechanisms

41

WHat is the indirect method of TRH control

High T4 and T3 levels cause the downregulation of TRH receptors on Thyrotrophs

42

What is the direct method of regulation

Low amounts of TSH released from Thyrotrophs

43

Know the slide about TSH regulation of thyroid function

ok

44

What is Cretinism

Dwarfism caused by endemic thyroid deficiency during development.
- Mental retardation
- short stature
- delayed motor development
Treatment within a few days of birth restores normal development
Treatment after this time restores physical development bu tnot mental development

45

Hashimoto thyroiditis

Anti-thyroid antibodies that block and destroy thyroid function
Presentation: Painless goiter, edema, headache

46

Graves Disease

Hyperthyroidism. Caused by Ig Antibodies that mimic Thyroid Stimulating hormone.
Antibodies continually bind to TSH receptors on the thyroid and continualy drive thyroid hormone production.
Wt loss, sweating, diarrhea, fatigue
Eyeball protrusion, dry epithelial layers, ulceration of the eye