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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
T/F T3 only binds to DNA?
False, it can also bind to ribosomes, mitochondria, plasma membrane to up the non genomic responses.
26
How does t3 and t4 enter the target cell?
facilitated diffusion | diffusion (standard)
27
is T3 associated with a HSP?
no
28
with increases in T3 you also see?
increased: (everything except muscle mass) a) metabolic rate b) oxygen consumption Decreased: a) muscle mass
29
T/F brain function increases with increased T3 levels?
True, but only with babies. Generally in adults, T3 does not affect the brain of testis.
30
T/F With T3 increases, you see increased anabolism and catabolism?
true
31
T3 and T4 in fetal development is required for what?
everything! especially: 1) promoting linear growth 2) promotes brain growth and function 3) tooth/skin/hair development
32
what do thyroid hormones do the free fatty acid levels in the blood?
elevates them
33
what do thyroid hormones do to the cholesterol levels in the blood?
it decreases them because more is being secreted into the bile.
34
what do you usually see with hypothyroidism?
increased cholesterol
35
T/F very high levels of thyroid hormones can cause weight loss?
true if high enough because it dramatically raises the BMR
36
what do thyroid hormones do to the heart?
1) increases heart rate 2) increases contractility 3) increases CO
37
increased levels of thyroid hormone can cause anxiety, and increased respiratory rates?
true
38
what do thyroid hormones do to the GI tract?
increases motility and secretions
39
Can Thyroid hormones cause osteoporosis?
Yes when in high concentrations
40
If you have constant lethargy and difficultly sleeping, what could this indicate about your thyroid levels?
thyroid hormone levels are high. | note hypothyroidism can cause lethargy as well but not generally sleeping problems
41
what are some sexual changes that happen with hyper/hypo excretion of thyroid hormone?
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
what generally causes hyperthyroidism?
thyroid adenoma or graves disease
43
would TSH levels be high or low in graves disease?
Low because of neg. feedback
44
when do you see exopthalmos?
only in graves disease and not with the adenoma
45
what are some common characteristics with hyperthyroidism?
``` intolerance to heat weight loss psychic disorders inability to sleep exothalmos (graves only) ```
46
what do thiouracil drugs do?
suppress T3 and T4 activity
47
What is thyroid storm?
a life threatening condition caused by untreated hyperthyroidism. Brought on by stress and can cause changes in alertness, tachycardia, heart failure, pulmonary edema.
48
what are some causes of hypothyroidism?
autoimmunity, endemic colloid goiter, non toxic colloid goiter.
49
what is myxedema?
``` bagginess under eyes and swelling of face. weight gain lethargy thin hair high cholesterol decreased BMR ```
50
what is myxedema coma?
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
what is cretinism?
lack of thyroid hormone in infants causing stunted growth, retardation, and enlargement of soft tissues.
52
what is the most common type of endocrine neoplasm?
thyroid cancer
53
T/F Thyroid cancer affects more women than men and is more common in Asians?
true
54
what often happens with a MEN2 gene mutation?
multiple endocrine neoplasms including the thyroid.
55
how do you treat thyroid cancer?
1) radioactive iodine | 2) thyroidectomy

HOS Final (12 decks)

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