Thyroid physiology Flashcards Preview

Physiology > Thyroid physiology > Flashcards

Flashcards in Thyroid physiology Deck (60):
1

Where are thyroid receptors found?

In virtually all tissues

2

What is the importance of thyroid hormone?

Maintenance of energy homeostasis and regulating energy expenditure

3

What are the physiological effects of thyroid hormone?

Stimulates cell metabolism and activity

4

What is the most common preventable cause of brain damage?

Iodine deficiency, causing a lack of thyroid hormone

5

What is the innervation of the thryroid?

• Sympathetic innervation: vasomotor but not secretomotor

6

What is the blood supply to the thyroid?

Bilateral superior and inferior thyroid arteries

7

What are the three, bilateral veins to the thyroid?

superior, middle and inferior

8

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

True

9

What is the functional unit of the thyroid gland?

Thyroid follicles

10

What type of epithelium surround thyroid colloid?

Simple cuboidal

11

What is the main constituent of thyroid follicles?

Thyroglobulin

12

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

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

13

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

Secrete Calcitonin

14

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

iodothyronines

15

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

2 months worth

16

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

Kidneys will hold onto more

17

• People with diets deficient in iodine can form what?

iodine deficiency goiter

18

Thyroid hormone is synthesized where?

In the colloid of the thyroid

19

What transports iodide into the thyroid epithelial cells?

Na/I symporter

20

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

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

21

Process of concentrating iodide in the cell is called what?

Iodide trapping

22

What happens to iodide when it enters the colloid?

Immediately oxidized to iodine and attached to tyrosine

23

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

Pendrin

24

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

Thyroglobulin, made up of Y residues

25

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

Organification

26

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

Thyroid peroxidase (TPO)

27

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

Low iodide

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?

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

29

Thyroxin = ?

T4

30

What is RT3? Is it active?

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

This is inactive.

31

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

Thyroid releasing hormone (TSH) stimulates thyrotrophs to release TSH

32

What is the feedback mechanism for TSH?

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

33

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

Stimulates the release of T4 and T3

1. Stimulates the iodide pump
2. Increases iodination of Y
3. Increase thyroid cells

34

What is the effect of stress on secretion?

Inhibited

35

What is the half-life of TSH?

~60 minutes

36

What causes a goiter?

TSH will stimulate hyperplasia of the thyroid

37

How is TSH transported in the blood?

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

38

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

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

39

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

Free form

40

What predominates in the circulation: T3 or T4?

T4

41

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

Serves as a store, and prevents loss through urination

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?

Thyroid hormone receptors located in the nucleus, bound to DNA.

These are energy dependent

43

Where is the thyroid hormone receptor bound?

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

44

Deficiency of thyroid hormone in kids causes what?

Failure of body growth, and MR

45

What is cretinism?

Disease caused by extreme hypothyroidism early in life

46

What is the hormone that converts T4 to T3?

Iodinase

47

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

Long time

48

What does hypothyroidism do to plasma [cholesterol]?

Increases

49

What does thyroid hormone do to cardiac output?

Increases

50

What is the clinical measurement of thyroid function?

TSH

51

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

TSH will be regulated via feedback inhibition

52

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

Increases

53

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

TSH receptors o the thyroid

54

Which causes menstrual irregularities: hyper or hypothyroidism?

Hyper

55

Which causes osteoporosis: hyper or hypothyroidism?

Hyperthyroidism

56

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

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

57

What is Hashimoto's thyroiditis?

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

58

Is Hashimoto's thyroiditis hyper or hypothyroidism?

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

59

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

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

60

What is Myxedema

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