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Physiology > Thyroid physiology > Flashcards

Thyroid physiology Flashcards

1
Q

Where are thyroid receptors found?

A

In virtually all tissues

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2
Q

What is the importance of thyroid hormone?

A

Maintenance of energy homeostasis and regulating energy expenditure

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3
Q

What are the physiological effects of thyroid hormone?

A

Stimulates cell metabolism and activity

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4
Q

What is the most common preventable cause of brain damage?

A

Iodine deficiency, causing a lack of thyroid hormone

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5
Q

What is the innervation of the thryroid?

A

• Sympathetic innervation: vasomotor but not secretomotor

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6
Q

What is the blood supply to the thyroid?

A

Bilateral superior and inferior thyroid arteries

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7
Q

What are the three, bilateral veins to the thyroid?

A

superior, middle and inferior

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8
Q

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

A

True

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9
Q

What is the functional unit of the thyroid gland?

A

Thyroid follicles

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10
Q

What type of epithelium surround thyroid colloid?

A

Simple cuboidal

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11
Q

What is the main constituent of thyroid follicles?

A

Thyroglobulin

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12
Q

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

A

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

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13
Q

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

A

Secrete Calcitonin

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14
Q

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

A

iodothyronines

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15
Q

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

A

2 months worth

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16
Q

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

A

Kidneys will hold onto more

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17
Q

• People with diets deficient in iodine can form what?

A

iodine deficiency goiter

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18
Q

Thyroid hormone is synthesized where?

A

In the colloid of the thyroid

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19
Q

What transports iodide into the thyroid epithelial cells?

A

Na/I symporter

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20
Q

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

A

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

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21
Q

Process of concentrating iodide in the cell is called what?

A

Iodide trapping

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22
Q

What happens to iodide when it enters the colloid?

A

Immediately oxidized to iodine and attached to tyrosine

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23
Q

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

A

Pendrin

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24
Q

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

A

Thyroglobulin, made up of Y residues

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25
Q

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

A

Organification

26
Q

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

A

Thyroid peroxidase (TPO)

27
Q

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

A

Low iodide

28
Q

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

A

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

29
Q

Thyroxin = ?

A

T4

30
Q

What is RT3? Is it active?

A

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

This is inactive.

31
Q

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

A

Thyroid releasing hormone (TSH) stimulates thyrotrophs to release TSH

32
Q

What is the feedback mechanism for TSH?

A

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

33
Q

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

A

Stimulates the release of T4 and T3

  1. Stimulates the iodide pump
  2. Increases iodination of Y
  3. Increase thyroid cells
34
Q

What is the effect of stress on secretion?

A

Inhibited

35
Q

What is the half-life of TSH?

A

~60 minutes

36
Q

What causes a goiter?

A

TSH will stimulate hyperplasia of the thyroid

37
Q

How is TSH transported in the blood?

A

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

38
Q

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

A

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

39
Q

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

A

Free form

40
Q

What predominates in the circulation: T3 or T4?

A

T4

41
Q

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

A

Serves as a store, and prevents loss through urination

42
Q

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

A

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

These are energy dependent

43
Q

Where is the thyroid hormone receptor bound?

A

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

44
Q

Deficiency of thyroid hormone in kids causes what?

A

Failure of body growth, and MR

45
Q

What is cretinism?

A

Disease caused by extreme hypothyroidism early in life

46
Q

What is the hormone that converts T4 to T3?

A

Iodinase

47
Q

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

A

Long time

48
Q

What does hypothyroidism do to plasma [cholesterol]?

A

Increases

49
Q

What does thyroid hormone do to cardiac output?

A

Increases

50
Q

What is the clinical measurement of thyroid function?

A

TSH

51
Q

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

A

TSH will be regulated via feedback inhibition

52
Q

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

A

Increases

53
Q

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

A

TSH receptors o the thyroid

54
Q

Which causes menstrual irregularities: hyper or hypothyroidism?

A

Hyper

55
Q

Which causes osteoporosis: hyper or hypothyroidism?

A

Hyperthyroidism

56
Q

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

A

[TSH] = low

[T4], [T5] = high

57
Q

What is Hashimoto’s thyroiditis?

A

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

58
Q

Is Hashimoto’s thyroiditis hyper or hypothyroidism?

A

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
Q

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

A 
Primary = prob w/ thyroid
Sec = prob with pituitary
Tert = Hypothalamus prob
60
Q

What is Myxedema

A

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

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