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HOS Final > 5 Thyroid endocrinology > Flashcards

5 Thyroid endocrinology Flashcards

1
Q

what do you find inside the thyroid follicles?

A

colloid AKA iodinated thyroglobulin

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2
Q

where do you find the parafollicular cells?

A

they are the clear cells that are scattered in between the follicles and they secrete calcitonin.

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3
Q

What is reverse T3?

A

the inactive form of T3

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4
Q

tyrosine + I2 equals what?

tyrosine + (2)I2 equals what?

A

1) Monoiodotyrosine (MIT)

2) Diiodotyrosine (DIT)

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5
Q

MIT + DIT equals what?
DIT + DIT equals what?
DIT + MIT equals what?

A

1) MIT + DIT = T3
2) DIT + DIT = T4
3) DIT + MIT = reverse T3

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6
Q

What is tetraiodothryronine?

A

Tetraiodothyronine=T4=thyroxine

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7
Q

on which side of the membrane is T3 released?

A

basolateral membrane

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8
Q

How does I2 get into the follicular cell?

A

Na+/I2 symport (NIS transporter)

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9
Q

how does the colloid get back into the follicular cells to release t3 and t4?

A

pinocytosis

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10
Q

What is the function of TPO in the follicular cell?

A

TPO= thyroid peroxidase
TPO converts iodide ions to iodine by oxidizing it.
Also binds together MIT/DIT with another MIT/DIT

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11
Q

Where is thyroglobulin made?

A

in the RER of the follicular cell.

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12
Q

What happens to the oxidized iodine?

A

it combines with the tyrosine residue on thyroglobulin to make MIT and DIT (colloid). It occurs on the apical membrane of the follicular cell.

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13
Q

Does T3 or T4 have the higher clearance rate? Half life?

A

T4 has the lower clearance rate and longer half life.

T3 has the higher clearance rate and shorter half life.

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14
Q

How is T3 and T4 transported in the blood?

A

1) Thyroxine binding globulin (TBG)
2) transthyretin (TTR delivers to CNS)
3) Free hormone (very little)

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15
Q

What is the major regulator for T3 and T4 release?

A

TSH

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16
Q

What does TSH do?

A

increases iodinated thyroglobulin breakdown
increased iodide pump
increased size/number of thyroid cells
increased T3 and T4 formation

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17
Q

where does TSH bind the follicular cells?

A

basolateral membrane

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18
Q

What happens to TRH expression with exposure to cold?

A

It goes up

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19
Q

what do high concentrations of blood iodine do to the thyroid gland?

A

decreases size and blood supply to gland
decrease iodide trapping
decrease formation of colloid

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20
Q

Thyroid hormones generally affect every cell in the body except?

A

1) brain

2) testis

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21
Q

Once released from the thyroid gland and near the target organ, what happens to the hormone?

A

it breaks apart from the TBG protein (carrier) and becomes T4. From there, within target tissue cytoplasm, T4 is deiodinated to form T3.

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22
Q

T/F T3 binds to the nuclear receptors with 10x higher affinity and activates or represses gene transcription?

A

true

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23
Q

The T3 receptor binds to DNA as a heterodimer/homodimer?

A

heterodimer unlike steroid hormones.

24
Q

T3 binds to the thyroid hormone receptor and heterodimerizes with what to bind to the thyroid response element?

A

retinoid X receptor (RXR)

25
Q

T/F T3 only binds to DNA?

A

False, it can also bind to ribosomes, mitochondria, plasma membrane to up the non genomic responses.

26
Q

How does t3 and t4 enter the target cell?

A

facilitated diffusion

diffusion (standard)

27
Q

is T3 associated with a HSP?

A

no

28
Q

with increases in T3 you also see?

A

increased: (everything except muscle mass)
a) metabolic rate
b) oxygen consumption

Decreased:
a) muscle mass

29
Q

T/F brain function increases with increased T3 levels?

A

True, but only with babies. Generally in adults, T3 does not affect the brain of testis.

30
Q

T/F With T3 increases, you see increased anabolism and catabolism?

A

true

31
Q

T3 and T4 in fetal development is required for what?

A

everything! especially:

1) promoting linear growth
2) promotes brain growth and function
3) tooth/skin/hair development

32
Q

what do thyroid hormones do the free fatty acid levels in the blood?

A

elevates them

33
Q

what do thyroid hormones do to the cholesterol levels in the blood?

A

it decreases them because more is being secreted into the bile.

34
Q

what do you usually see with hypothyroidism?

A

increased cholesterol

35
Q

T/F very high levels of thyroid hormones can cause weight loss?

A

true if high enough because it dramatically raises the BMR

36
Q

what do thyroid hormones do to the heart?

A

1) increases heart rate
2) increases contractility
3) increases CO

37
Q

increased levels of thyroid hormone can cause anxiety, and increased respiratory rates?

A

true

38
Q

what do thyroid hormones do to the GI tract?

A

increases motility and secretions

39
Q

Can Thyroid hormones cause osteoporosis?

A

Yes when in high concentrations

40
Q

If you have constant lethargy and difficultly sleeping, what could this indicate about your thyroid levels?

A

thyroid hormone levels are high.

note hypothyroidism can cause lethargy as well but not generally sleeping problems

41
Q

what are some sexual changes that happen with hyper/hypo excretion of thyroid hormone?

A

high=impotence in male, and oligomenorrhea (infrequent menstruation) in female.

Low= loss of libido in male and female, and excessive or frequent menstruation in females.

42
Q

what generally causes hyperthyroidism?

A

thyroid adenoma or graves disease

43
Q

would TSH levels be high or low in graves disease?

A

Low because of neg. feedback

44
Q

when do you see exopthalmos?

A

only in graves disease and not with the adenoma

45
Q

what are some common characteristics with hyperthyroidism?

A 
intolerance to heat
weight loss
psychic disorders
inability to sleep
exothalmos (graves only)
46
Q

what do thiouracil drugs do?

A

suppress T3 and T4 activity

47
Q

What is thyroid storm?

A

a life threatening condition caused by untreated hyperthyroidism. Brought on by stress and can cause changes in alertness, tachycardia, heart failure, pulmonary edema.

48
Q

what are some causes of hypothyroidism?

A

autoimmunity, endemic colloid goiter, non toxic colloid goiter.

49
Q

what is myxedema?

A 
bagginess under eyes and swelling of face. 
weight gain
lethargy
thin hair
high cholesterol
decreased BMR
50
Q

what is myxedema coma?

A

a condition that usually occurs in older people as a result of not taking thyroid medications. Causes them to develop hypothermia and slip into a coma.

51
Q

what is cretinism?

A

lack of thyroid hormone in infants causing stunted growth, retardation, and enlargement of soft tissues.

52
Q

what is the most common type of endocrine neoplasm?

A

thyroid cancer

53
Q

T/F Thyroid cancer affects more women than men and is more common in Asians?

A

true

54
Q

what often happens with a MEN2 gene mutation?

A

multiple endocrine neoplasms including the thyroid.

55
Q

how do you treat thyroid cancer?

A

1) radioactive iodine

2) thyroidectomy

HOS Final (12 decks)

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