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Endocrine > Thyroid physiology > Flashcards

Thyroid physiology Flashcards

1
Q

Which hormones does the thyroid secrete?

A

Thyroxine
Tri-iodothyronine
Calcitonin

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2
Q

What number is given to thyroxine?

A

T4

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3
Q

What number is given to tri-iodothyronine?

A

T3

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4
Q

Which hormones does the parathyroid gland secrete?

A

Parathyroid hormone

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5
Q

Which cells within the thyroid are responsible for producing T4 and T3?

A

Follicle cells

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6
Q

Histologically, how are follicle cells described?

A

simple cuboidal epithelial

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7
Q

What structure are the follicular cells surrounding?

A

Colloid

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8
Q

Which cells are scattered around the follicular cells?

A

Parafollicular C cells

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9
Q

What do parafollicular C cells secrete?

A

Calcitonin

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10
Q

Which receptors respond to TSH?

A

Thyrotopin

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11
Q

Describe iodines pathway to the colloid?

A

Diffuses across the endothelium from capillaries to the follicular cell and diffuses again to the colloid

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12
Q

How many units can DIT link to?

A

2

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13
Q

By what mechanism does thyroglobulin leave the colloid?

A

Pinocytosis

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14
Q

How are T3 and T4 released from thyroglobulin?

A

Enzymatic degeneration by lysosomes which releases thyroglobulin into T3 and T4

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15
Q

Which amino acid does iodine attach to in the follicle?

A

Tyrosine

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16
Q

What is formed when iodine and tyrosine attach?

A

MIT

DIT

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17
Q

What is formed when MIT and DIT couple?

A

T3

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18
Q

What is formed when 2 DITs couple together?

A

T4

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19
Q

Where are T3 and T4 stored?

A

In colloid thyroglobulin

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20
Q

Which hormone is the biologically active one?

A

T3

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21
Q

Where is T4 converted to T3?

A

Liver and kidney

22
Q

Which of the hormones are most abundant?

A

T4 (90%)

23
Q

What plasma proteins do T3 and T4 bind to?

A

TBG
TBPA
Albumin

24
Q

Why do T3/4 bind to plasma proteins?

A

They are hydrophobic

25
Q

What happens when T3 and T4 are bound to plasma proteins?

A

They are inactive.

26
Q

Does pregnancy increase or decrease T4?

A

Increases total. No effect on free

27
Q

Does corticosteroids increase or decrease T4?

A

Decreases total. No effect on free

28
Q

Does hepatitis A increase or decrease T4?

A

Increases total. No effect on free

29
Q

What effect do anti-epileptics have on T4?

A

Decrease total. No effect on free

30
Q

Why does hyperthyroidism cause weight loss?

A

Increased BMR due to increased number and size of mitochondria therefore increased ATP hydrolysis

31
Q

Which hormone, important in children, relies on the presence of thyroid hormones?

A

Growth hormone releasing hormone and therefore growth hormone

32
Q

Which hormone, used in regulating thyroid hormones, is produced in the hypothalamus?

A

Thyrotrophin releasing hormone

33
Q

What does TRH stimulate the release of?

A

TSH

34
Q

Where does TSH live?

A

Anterior pituitary

35
Q

What does TSH do?

A

Stimulates release of T3 and T4

36
Q

How is the negative feedback loop closed?

A

Presence of T3 and T4

37
Q

When are thyroid hormones at their highest levels?

A

Late at night

38
Q

What causes exopthlamos?

A

Water retaining carbohydrate build up behind the eyes

39
Q

Physiologically, why might a hypothyroid be cold?

A

Thyroid hormones involved in thermogenesis.

40
Q

When is propanolol used in hyperthryoidism?

A

To reduce sympathetic effects e.g. increased HR

41
Q

During pregnancy, what is the effect of the mother being hypothyroid?

A

Low IQ of baby

42
Q

Which is of greater significance:

Diurnal rhythm in cortisol or in thyroid hormones?

A

Cortisol

43
Q

Which part of the thyroid connects the right and left lobe?

A

Isthmus

44
Q

Apart from T3 and T4 what else does the thyroid secrete?

A

Calcitonin

45
Q

What is the role of calcitonin?

A

Regulates calcium

46
Q

True or False

An underactive thyroid causes heat intolerance

A

False.

Causes cold intolerance

47
Q

Which antibodies can interfere with thyroid measurement?

A

Heterophile antibodies

48
Q

Why does a raised TSH cause hypothyroidism?

A

Too much TSH causes negative feedback. No TSH then can’t release T3/4

49
Q

When is TSH tests not reliable?

A

If a primary problem with anterior pituitary or hypothalamus

50
Q

If TSH is suppressed what is the condition present?

A

Hyperthyroid

Endocrine (20 decks)

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