Thyroid physiology

Question 1

Where are thyroid receptors found?

Answer 1

In virtually all tissues

Question 2

What is the importance of thyroid hormone?

Answer 2

Maintenance of energy homeostasis and regulating energy expenditure

Question 3

What are the physiological effects of thyroid hormone?

Answer 3

Stimulates cell metabolism and activity

Question 4

What is the most common preventable cause of brain damage?

Answer 4

Iodine deficiency, causing a lack of thyroid hormone

Question 5

What is the innervation of the thryroid?

Answer 5

• Sympathetic innervation: vasomotor but not secretomotor

Question 6

What is the blood supply to the thyroid?

Answer 6

Bilateral superior and inferior thyroid arteries

Question 7

What are the three, bilateral veins to the thyroid?

Answer 7

superior, middle and inferior

Question 8

True or false: when the thyroid gland is very large can hear noise from gland (bruit)

Answer 8

True

Question 9

What is the functional unit of the thyroid gland?

Answer 9

Thyroid follicles

Question 10

What type of epithelium surround thyroid colloid?

Answer 10

Simple cuboidal

Question 11

What is the main constituent of thyroid follicles?

Answer 11

Thyroglobulin

Question 12

What are the two storage forms of thyroglobulin? Which is more active?

Answer 12

T3 and T4, with T3 the more active/potent one

Question 13

What is the role of the parafollicular cells in the thyroid?

Answer 13

Secrete Calcitonin

Question 14

Most of the iodide in the body is stored in the thyroid in the form of what?

Answer 14

iodothyronines

Question 15

How big of a store of Iodine does the thyroid contain?

Answer 15

2 months worth

Question 16

What is the regulatory mechanism that occurs when plasma iodine levels fall?

Answer 16

Kidneys will hold onto more

Question 17

• People with diets deficient in iodine can form what?

Answer 17

iodine deficiency goiter

Question 18

Thyroid hormone is synthesized where?

Answer 18

In the colloid of the thyroid

Question 19

What transports iodide into the thyroid epithelial cells?

Answer 19

Na/I symporter

Question 20

Expression of the gene for NIS is inhibited by what and stimulated by what?

Answer 20

Expression of the gene for NIS is inhibited by iodide and stimulated by TSH.

Question 21

Process of concentrating iodide in the cell is called what?

Answer 21

Iodide trapping

Question 22

What happens to iodide when it enters the colloid?

Answer 22

Immediately oxidized to iodine and attached to tyrosine

Question 23

What is the transporter that transports iodide from the apical membrane to the lumen of the follicle?

Answer 23

Pendrin

Question 24

What is the storage molecule for Iodine? What is the amino acid that this molecule is made up of?

Answer 24

Thyroglobulin, made up of Y residues

Question 25

• The process of binding iodine with the thyroglobulin is called what?

Answer 25

Organification

Question 26

What is the enzyme that is responsible for the formation of MIT, DIT, T3 and T4 from thyroglobulin and iodine?

Answer 26

Thyroid peroxidase (TPO)

Question 27

T3 formation is favored (relative to T4) under what conditions?

Answer 27

Low iodide

Question 28

What are the steps of secretion of thyroglobulin? What is the receptor utilized to bring T3 back into the epithelial cell from the colloid?

Answer 28

Binding of thyroglobulin to megalin, then endocytosis and lysosomal degradation in the thyroid epithelial cell

Question 29

Thyroxin = ?

Answer 29

T4

Question 30

What is RT3? Is it active?

Answer 30

Reverse T3, where the Iodides are distributed in the opposite way as in regular T3. This is inactive.

Question 31

What is the molecule release from the hypothalamus that plays a role in the regulation of the thyroid? What does it do?

Answer 31

Thyroid releasing hormone (TSH) stimulates thyrotrophs to release TSH

Question 32

What is the feedback mechanism for TSH?

Answer 32

T3 feeds back into the anterior pituitary and the hypothalamus to inhibit TSH production

Question 33

What is the function of TSH? How does it do this?(3)

Answer 33

Stimulates the release of T4 and T3 1. Stimulates the iodide pump 2. Increases iodination of Y 3. Increase thyroid cells

Question 34

What is the effect of stress on secretion?

Answer 34

Inhibited

Question 35

What is the half-life of TSH?

Answer 35

~60 minutes

Question 36

What causes a goiter?

Answer 36

TSH will stimulate hyperplasia of the thyroid

Question 37

How is TSH transported in the blood?

Answer 37

Bound to plasma proteins--specifically, thyroxine binding globulin (TBG)

Question 38

What is transthyretin (TTR)?What two things does it bind to?

Answer 38

an additional semi-specific thyroid-binding protein found in the plasma, that can also bind retinol

Question 39

What is the form of T3/T4 that actually interacts with target cells?

Answer 39

Free form

Question 40

What predominates in the circulation: T3 or T4?

Answer 40

T4

Question 41

What is the purpose of having T3/T4 bound to proteins in the plasma? (2)

Answer 41

Serves as a store, and prevents loss through urination

Question 42

What are the receptors that take up T3/T4 into target cells? Where on/in the cell are they located? Are they energy dependent?

Answer 42

Thyroid hormone receptors located in the nucleus, bound to DNA. These are energy dependent

Question 43

Where is the thyroid hormone receptor bound?

Answer 43

To the Thyroid hormone response element on the cell's DNA

Question 44

Deficiency of thyroid hormone in kids causes what?

Answer 44

Failure of body growth, and MR

Question 45

What is cretinism?

Answer 45

Disease caused by extreme hypothyroidism early in life

Question 46

What is the hormone that converts T4 to T3?

Answer 46

Iodinase

Question 47

How long does it take for T3/T4 to take effect (relatively)?

Answer 47

Long time

Question 48

What does hypothyroidism do to plasma [cholesterol]?

Answer 48

Increases

Question 49

What does thyroid hormone do to cardiac output?

Answer 49

Increases

Question 50

What is the clinical measurement of thyroid function?

Answer 50

TSH

Question 51

Why is [TSH] high in hypothyroidism, and low in hyperthyroidism?

Answer 51

TSH will be regulated via feedback inhibition

Question 52

What happens to the number of beta receptors on the heart with increases in TSH?

Answer 52

Increases

Question 53

What are the receptors that are stimulated in Grave's disease?

Answer 53

TSH receptors o the thyroid

Question 54

Which causes menstrual irregularities: hyper or hypothyroidism?

Answer 54

Hyper

Question 55

Which causes osteoporosis: hyper or hypothyroidism?

Answer 55

Hyperthyroidism

Question 56

What are the lab values ([TSH], [T4], [T3]) for someone with hyperthyroidism?

Answer 56

[TSH] = low | [T4], [T5] = high

Question 57

What is Hashimoto's thyroiditis?

Answer 57

Type of hypothyroidism where there are autoimmune antibodies directed against thyroglobulin or thyroid peroxidase

Question 58

Is Hashimoto's thyroiditis hyper or hypothyroidism?

Answer 58

Hyper first if there is an acute immune response. This will be followed by hypothyroidism. If there is no acute response, could be mild hyperthyroidism, followed by long term hypothyrodisim

Question 59

What is the difference between primary and secondary hypothyroidism? Tertiary?

Answer 59

``` Primary = prob w/ thyroid Sec = prob with pituitary Tert = Hypothalamus prob ```

Question 60

What is Myxedema

Answer 60

deposition of mucopolysaccharides in the dermis, which results in swelling of the affected area. This is seen in hypo/hyperthyroidism