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Endocrine > Thyroid 1 > Flashcards

Thyroid 1 Flashcards

1
Q

What does the thyroid gland secrete?

A

Thyroxine (T4), Tri-iodothyronine (T3), Calcitonin

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2
Q

What do the parathyroid glands secrete?

A

PTH

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3
Q

What structure makes up the thyroid gland?

A

Follicles

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4
Q

What makes up follicles?

A

Follicular cells and inner colloid

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5
Q

What is the colloid?

A

Tyrosine containing thyroglobulin filled spheres enclosed by follicular cells

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6
Q

What do parafollicular C cells secrete?

A

Calcitonin

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7
Q

What happens in iodide sequestration?

A

Inorganic iodide is trapped by the gland by an enzyme dependent system, oxidised and incorporatd into the glyco protein thyroglobulinto form mono and diiodotyrosine, thyroid hormone precursors.

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8
Q

What coupling occurs after the production of MIT and DIT, and where are they stored?

A

MIT+DIT (T3), AND 2 DITs(T4) which are stored in colloid thyroglobulin till required

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9
Q

How much of the thyroid hormones secreted is T4?

A

~90%

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10
Q

How many times more potent is T3 than T4?

A

Roughly 4x

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11
Q

What organs convert T4 to T3?

A

Liver, kidney, (and muscle)

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12
Q

How do T3 and T4 move from the colloid to follicular cell?

A

Pinocytosis

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13
Q

Why do T3 and T4 bind to plasma proteins when released from follicular cells?

A

As they are hydrophobic and lipophilic

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14
Q

What plasma proteins do T3 and T4 bind to in the blood stream?

A

Thyroxine binding globulin (around 70%), Thyroxine binding prealbumin (TBPA around 20%), albumin (around 5%)

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15
Q

In what form at T3 and T4 biologically active?

A

Unbound

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16
Q

How much less avidly is T3 bound by TBG and TTR than T4?

A

10-20x less avidly by TBG, and not significantly at all by TTR

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17
Q

What does an increased /decreased TBG level cause?

A

Increased/decreased total T4 but not free T4

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18
Q

What are some causes of an increased TBG?

A

Pregnancy, newborn state, oestrogen sources, Tamoxifen, Hep A

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19
Q

What are some causes of decreased TBG?

A

Androgens, large doses glucocorticoids, Cushings S, active acromegaly, severe systemic illness

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20
Q

What do carbimazole and propylthiouracil inhibit in the treatment of hyperthyroidism?

A

Iodine attachment to tyrosine residues to form MIT and DIT

21
Q

What do thyroid hormones do the basal metabolic rate and thermogenesis?

A

Increase them

22
Q

What do thyroid hormones do to carbohydrate metabolism?

A

Increase blood glucose, and increase insulin-dependent glucose uptake into cells

23
Q

What do thyroid hormones do to lipid metabolism?

A

Mobilise fats from adipose tissue, increase fatty acid oxidation in tissues

24
Q

What do thyroid hormones do to protein metabolism?

A

Increase protein synthesis

25
Q

Why are thyroid hormones important in growth?

A

GHRH production and secretion, glucocorticoid-induced GHRH release and GH/somatomedins require thyroid hormones or the presence of them for activity

26
Q

How do thyroid hormones effect development of foetal and neonatal brain?

A

Myelinogenesis & axonal growth require thyroid hormones

27
Q

What are the effects of thyroid hormone on the sympathetic nervous system?

A

Increased catecholamine sensitivity and B-adrenergic receptor numbers in heart, skeletal muscle, adipose cells and lymphocytes, and decrease cardiac alpha-adrenergic receptors

28
Q

What are the effects of thyroid hormone on the CVS?

A

Increases HR and CO

29
Q

What stimulates TSH release from anterior pituitary?

A

Thyrotrophin releasing hormone (TRH) from hypothalamus

30
Q

What do low temperatures do to thyroid hormone regulation?

A

In babies/young children, cold environments stimulate TRH release, stimulates TSH release so increases T3 and T4 release

31
Q

What does stress do in thyroid hormone regulation?

A

Inhibits TRH and TSH

32
Q

What is the circadian rhythm in thyroid hormone production?

A

Highest late at night, lowest in morning

33
Q

What subfamily of enxzymes are important in the activation/deactivation of thyroid hormone at tissue level?

A

Delodinase enzymes (Type 1,2,3)

34
Q

How do delodinase enzymes make thyroid hormone inactive?

A

Addition or removal of an iodine atom in outer ring

35
Q

What delodinase enzyme activates T4 to T3 in tissues?

A

D2

36
Q

Where is D1 found?

A

Commonly in liver and kidney

37
Q

Where is D2 found?

A

Heart, skeletal muscle, CNS, fat, thyroid, pituitary

38
Q

Where is D3 found?

A

Fetal tissue, placenta, brain (except pituitary)

39
Q

What are the most common types of thyroid cancer?

A

Papillary (76%), follicular (17%)

40
Q

What hormone drives DTC?

A

TSH

41
Q

iS DTC more commen in men or women?

A

Women

42
Q

What are the differentiated thyroid cancers?

A

Papillary and follicular

43
Q

How does papillary thyroid cancer spread and where to?

A

Via lymphatics-local spread. Haematogenous spread to lungs, bone, liver and brain

44
Q

What thyroid condition is papillary thyroid cancer associated with?

A

Hashimoto’s thyroiditis

45
Q

What is the prognosis of papillary thyroid cancer?

A

Good-better if young and female

46
Q

How does follicular carcinoma tend to spread?

A

Haematogenously to lung and bone.

47
Q

What is the prognosis of follicular carcinoma?

A

Good

48
Q

What investigations are required in DTC?

A

After initial thyroid tests, US guided FNA, can involve excision biopsy of LN

49
Q

What is the usual management of DTC?

A

Surgery- lobectomy with isthmusectomy, sub-total or total thyroidectomy

Endocrine (14 decks)

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