The Thyroid Gland

Question 1

What is the basic anatomy of the thyroid gland?

Answer 1

Butterfly shaped gland in the anterior neck , situated just below the larynx

Question 2

How much does it weigh?

Answer 2

15-20g

Question 3

What two hormones does the thyroid gland produce?

Answer 3

Triiodothyronine and Thyroxine, T3 and T4 respectively

Question 4

What 2 types of cells can be found in the thyroid gland?

Answer 4

C(clear) cells

Follicular cells

Question 5

What do clear cells secrete?

Answer 5

Calcitonin and calcium regulating hormone

Question 6

What do follicular cells do?

Answer 6

Support thyroid hormone synthesis and surround follicles

Question 7

What are follicular cells?

Answer 7

Spherical structures whose walls are made of a spherical structure and the centre is filled with colloid

Question 8

What is colloid?

Answer 8

A sticky glycoprotein matrix that is in the centre of follicular cells

Question 9

How long a supply of thyroid hormone do we have?

Answer 9

2-3 months

Question 10

what is the function of a follicular cell?

Answer 10

1. manufactures the enzymes that make thyroid hormones and thyroglobulin
2. Concentrate iodide from the plasma and transport it to the colloid where it combines with tyrosine residues to form thyroid hormones

Question 11

In the formation of thyroid hormones how is iodide brought into the cell?

Answer 11

Via a sodium iodide symporter along with a coupled sodium channel to allow the cells to take up iodide against the concentration gradient

Question 12

Once within the cell, how is iodide transported into the colloid?

Answer 12

Via the pendrin transporter

Question 13

What do follicular cells synthesis in the cell membrane for addition to the iodide?

Answer 13

Enzymes and thyroglobulin which is tranported to the colloid

Question 14

In the colloid what happens to thyroglobulin and iodide?

Answer 14

The enzyme thyroid peroxidase combines the two to make T3 and T4

Question 15

What is monoiodotyrosine?

Answer 15

The addition of one iodine molecule to tyrosine

Question 16

If two iodine molecules are added to thyroglobulin then what is formed?

Answer 16

Diiodotyrosine

Question 17

What is the fate of the produced thyroid hormones?

Answer 17

Move across the cell membranes onto protein carrier, they are eventually released into the blood

Question 18

What protein do the thyroid hormones bind to?

Answer 18

Thyroxine-binding globulin

Question 19

Are T3 and T4 lipid or water soluble?

Answer 19

Lipid soluble

Question 20

What is the advantage of being bound to plasma protein?

Answer 20

Protection from degradation

Increased half-life

Question 21

What percentage of circulating thyroid hormones are bound?

Answer 21

99.8%

Question 22

What stimulates the movement of TH from the colloid to the plasma

Answer 22

TSH from the pituitary - stimulates the follicular cells to endocytose colloidal thyroglobulin. When not stimulated, the thyroid hormones are stored in the colloid.

Question 23

For with thyroid hormone does thyroxine binding hormone have a particularly high affinity for?

Answer 23

T4

Question 24

How do thyroid hormones bring about an effect?

Answer 24

By binding to nuclear receptor in the target cells, changing transcription and translation to alter protein synthesis

Question 25

Give 5 functions of the thyroid hormones

Answer 25

``` Raises metabolic rate Promotes thermogenesis Increases hepatic gluconeogenesis Net increase of proteolysis Net increase in lipolysis ```

Question 26

Give 2 outcomes of deficiency in thyroid hormone

Answer 26

Lack results in retarded growth because it is anabolic and stimulates the GH receptor expression Congenital hypothyroidism - required for brain development

Question 27

Define hyperthyroidism and give an example of the cause

Answer 27

Excess thyroid hormone - graves disease

Question 28

Define hypothyroidism and give an example of the cause

Answer 28

Deficiency in thyroid hormone - Hashimoto's disease