Thyroid Hormones

Question 1

What are the two lateral lobes attached by?

Answer 1

Isthmus

Question 2

What are thyroid epithelial cells?

Answer 2

Through the cells responsible for the synthesis of thyroid hormones and are arranged in Spears called thyroid follicles

Question 3

What are the follicles filled with?

Answer 3

Filled with colloid which contains thyroglobulin which is the storage form of thyroid hormones

Question 4

What’s T4?

Answer 4

Thyroxine (aka Tetraiodothyronine) – 90% of the hormones secreted

Question 5

What’s T3

Answer 5

Triiodothyronine – 9% of the hormones secreted

Question 6

Which thyroid hormone is the biologically active one?

Answer 6

T3 is. T4 is converted to T3

Question 7

What is the purpose of iodine?

Answer 7

Iodine is important for normal quantities of thyroid hormone to be produced.

Question 8

What’s the iron concentration like inside and outside of the cell?

Answer 8

30 x higher inside … iodide pump carries iodine from outside to inside

Question 9

What’s thyroglobulin?

Answer 9

It’s a large glycoprotein composed of 140 tyrosine amino acids. Thyroid hormones are formed within the thyroglobulin.

Question 10

Explain the pathway of thyroglobulin

Answer 10

Thyroglobulin is produced by follicular epithelial cells and pass through ER. It’s there stored in a membrane bound vesicles then it diffuses into lumen

Question 11

Explain the oxidation of iodide

Answer 11

Iodide enters the follicular cell. It’s then oxidized by an enzyme called thyroid peroxidase, which is found on the lumen surface, oxidized iodide is formed.

Question 12

What’s organification?

Answer 12

It’s the binding of iodine with the thyroglobulin active iodide added to tyrosine residues of thyroglobulin

Question 13

What is tyrosine first iodized to?

Answer 13

Monoiodotyrodine (MIT) and diiodotyrosine (DIT)

Question 14

What is coupling?

Answer 14

Coupling is when 2 iodotyrosine residues become coupled with each other

Question 15

2 DITs couple to make ___

Answer 15

T4

Question 16

1 DIT and 1 MIT couple to form ___

Answer 16

T3

Question 17

Where are thyroid hormones stored?

Answer 17

As part of the TG in the lumen of the follicle (colloid)

Question 18

How does thyroid hormone secretion occur?

Answer 18

First, apical surface sends out pseudopod extensions and a small portion of the colloid closes to form an endosome for endocytosis, then there’s a fusion of the endosome with the lysosome. Proteinases digest thyroglobulin and release T4 and T3.

Question 19

What plasma proteins do thyroxine bind to?

Answer 19

Globulin and prealbumin mainly, but also albumin (to a low affinity)

Question 20

How is T4 converted to T3

Answer 20

by the process of deiodination

Question 21

What is TSH couple to

Answer 21

Adenylate cyclase

Question 22

What regulates TSH secretion?

Answer 22

Electrical stimulation of hypothalamus increases, colt temp, emotional reactions

Question 23

How do you thyroid hormones work?

Answer 23

Binding with thyroid hormones the receptors become activated and initiate transcription in the nucleus

Question 24

What do thyroid hormones do

Answer 24

Increases synthesis of enzymes proteins etc. Essentially works to increase transcription in nucleus

Increases oxygen consumption and increases ion transport and glucose transport

Question 25

How does TH affect metabolism

Answer 25

Increases carb metabolism by increasing rate of absorption in intestine and increases rate of transport to the cells

Enhances fat metabolism through lipid mobilization from fat tissue and increases plasma free fatty acids

Question 26

What happens when there’s an excess of TH

Answer 26

protein catabolism and therefore muscle tremor

Question 27

What’s exophthalmos

Answer 27

Protrusion of eyeballs

Question 28

What’s Graves Disease

Answer 28

It’s an autoimmune disease in which the immune system produces antibodies that stimulates TSH Receptors of the thyroid gland.