Thyroid Physiology

Question 1

Thyroid means

Answer 1

shield

Question 2

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

Answer 2

• Can be seen and palpated during routine physical.

- Has a trace element, iodine

Question 3

Microscopic stucture of thyroid gland

Answer 3

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

Question 4

What does Colloid contain

Answer 4

Thyroglobulin

Question 5

What do parafollicular cells generate

Answer 5

calcitonin

Question 6

The six steps of thyroid hormone synthesis

Answer 6

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

Question 7

Iodide is present in most of our food

Answer 7

true

Question 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?

Answer 8

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

Question 9

What can inhibit the uptake of iodide?

Answer 9

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

Question 10

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

Answer 10

Pendrin

Question 11

THyroglobulin is made where?

Answer 11

In the Colloid

Question 12

What is the surface of the colloid layer coated in>

Answer 12

Thyroid Peroxidase

Question 13

What is the purpose of thyroid peroxidase

Answer 13

oxidizes iodide to iodine

Question 14

Iodine then does what to thyroglobulin

Answer 14

reacts with the tyrosine residues to “iodinate them”

Question 15

Internal rearrangement of two iodinate tyrosyl residues results in

Answer 15

Iosothyronine. This is catalyzed by thyroid peroxidase

Question 16

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

Answer 16

they are inactive

Question 17

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

Answer 17

ok

Question 18

This endocytosed colloid fuses with what

Answer 18

a native lysosome forming a lysoendosome

Question 19

What happens inside the lysoendosome

Answer 19

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

Question 20

Iodide is recycled?

Answer 20

Yes

Question 21

90% of what is released into the bloodstream is

Answer 21

T4, 10% T3….KNOW THIS

Question 22

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

Answer 22

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

Question 23

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

Answer 23

Steroid Use

Question 24

What kinds of things increase the amount of TBG?

Answer 24

Pregnancy, heroin use

Question 25

Which is more active, T3 or T4?

Answer 25

T3

Question 26

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

Answer 26

Two iodines

Question 27

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

Answer 27

Reverse T3

Question 28

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

Answer 28

5/3- Deiodinase

Question 29

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

Answer 29

Type 1 and type 2

Question 30

Type 1 deiodinase is found where?

Answer 30

Liver, Kidney, Thyroid

Question 31

Type 2 deiodinase is found where?

Answer 31

Pituitary, CNS, Placenta

Question 32

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

Answer 32

Type 1

Question 33

Thyroid hormone is a peptide

Answer 33

KNOW

Question 34

All peptide hormones have what type of Receptor? EXCEPT THYROID

Answer 34

ALL have a plasma membrane receptor except thyroid

Question 35

Thyroid hormone has what type of receptor

Answer 35

nuclear

Question 36

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

Answer 36

Acts directly on the DNA to regulate transcription

Question 37

Why does hyperthyroidism (physiologically) increase metabolism

Answer 37

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

Question 38

Increases in TRH lead to increases in TSH

Answer 38

truth

Question 39

TRH acts on what cells where

Answer 39

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

Question 40

How are TRH and TSH levels controlled

Answer 40

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

Question 41

WHat is the indirect method of TRH control

Answer 41

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

Question 42

What is the direct method of regulation

Answer 42

Low amounts of TSH released from Thyrotrophs

Question 43

Know the slide about TSH regulation of thyroid function

Answer 43

ok

Question 44

What is Cretinism

Answer 44

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

Question 45

Hashimoto thyroiditis

Answer 45

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

Question 46

Graves Disease

Answer 46

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