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Clinical Chemistry > Thyroid gland > Flashcards

Thyroid gland Flashcards

1
Q

thyroid anatomy

A

in the neck, bilobular form w/ central isthmus -‘butterfly’

follicular cells & C cells

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2
Q

Follicular cells

A

make thyroglublin
trap iodine
produce MIT & DIT
store T3 & T4 for release when TSH stimulation occurs

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3
Q

C cells

A

make clacitonin

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4
Q

thyroid hormone precursor

A

tyrosine residue on the thyroglobulin

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5
Q

Iodine involvement in thyroid hormones

A

iodide is oxidized to iodine via thyroid peroxidase (TPO) & attaches to the tyrosine residue

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6
Q

T3 2 base components

A

MIT + DIT

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7
Q

T4 2 base components

A

DIT + DIT

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8
Q

TSH stimulation on T3 & T4

A

the stored T3 & T4 are cleaved from thyroglobulin droplet via lysosome ingestion when TSH stimulates thyroid

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9
Q

MIT

A

3-monoiodiotyrosine

has one iodine in 3’ position on ring

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10
Q

DIT

A

3,5-diiodotyrosine

has 2 iodines on 3’ & 5’ position on ring

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11
Q

biologically active thyroid hormone

A

T3 is the most biologically active form: where iodine is missing from the OUTER ring
T4- significantly less active
T3r- removal of iodine from inner ring & has NO BIOLOGICAL ACTIVITY

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12
Q

regulation of thyroid

A

hypothalamus secretesTRH
pituitary secretes TSH
thyroid gland releases T4 & T3 into circulation
thyroid hormones feedback & shut off TRH & TSH

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13
Q

5’-deiodinase

A

responsible for taking of an iodine off T4 into T3 or T3r

3 types

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14
Q

type 1 5’-deiodinase

A

MOST ABUNDANT
located in liver & kidney!
susceptible to some drugs

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15
Q

type 2 5’-deiodinase

A

located in brain & pituitary

keeps T3 constant level in the brain

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16
Q

type 3 5’-deiodinase

A

form deiodinates T3 to T2 & becomes completely inactive

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17
Q

transport of thyroid hormones

A

TBG: thyroxine-binding globulin; MOST ABUNDANT
TBPA: thyroid-binding pre-albumin
albumin

higher the levels of TBG, the higher the T4 & T3 levels of bound hormone

18
Q

free T3 levels in the blood

A

0.4%

19
Q

thyroid hormone cell action

A
  1. enters cell via thyroid hormone transporter
  2. if T4 a 5’-deiodinase will convert to T3 OR if T3 it will either move on or will be converted to T2
  3. T3 binds to thyroid nuclear receptor(TR) in nucleus
  4. complex causes the alignment of RXR(thyroid responsive gene) & TRE (thyroid responsive element) and forms a protein of ‘action’
    THYROID HORMONES ARE PROTEIN BASED BUT ACT LIKE STEROIDS!!
20
Q

thyroid hormones affect

A 
tissue growth
brain maturation
body heat production
increase 02 consumption
increase b-adrenergic receptors
21
Q

thyroid effects

A

metabolic- increase in 02 consumption, protein catabolism, glucose levels
cardiovascular - increase heart rate, cardiac output, blood volume & decrease in peripheral vascular resistance
CNS- increase in adrenergic activity & sensitivity
GI- increase in motility

22
Q

thyroid stimulating hormone TSH assay

A

3rd generation test method
detects 0.01 mU/L
chemiluminometric assay

23
Q

serum total T4 or serum total T3 assay

A

RIA, chemiluminometric or immunometric

24
Q

free thyroxine or free T4 or free triiodo-thyronine or free T3 assay

A

dialysis kit method

25
Q

thyroglobulin assay

A

should not be in circulation bc they are in the thyroid

used to diagnose thyroid cancers

26
Q

thyroid binding globulin TGB assay

A

may rise in pregnancy & may go down in some diseases
used to determine free hormones
total-TBG
not used very often

27
Q

thyroid stimulating antibody or TSAb or TSI

A

no TSH but thyroid TSH receptor is being activated by antibody

28
Q

TSH receptor antibodies - TRAb or TSHR-Ab

A

can be stimulating or blocking antibody as it competitively binds to TSH receptor

29
Q

Anti-thyroid peroxidase antibody or Anti-TPO Ab

A

attacks TPO which helps form thyroid hormones & process them

30
Q

Graves disease general

A

most common hyperthyroidism- increased T3/T4 & low TSH
positive for TSHR-Ab 70-100% of the cases
may develop anti-TPOAb
women > men

31
Q

Hashimoto’s thyroiditis general

A

hypothyroidism - low T3/T4 & high TSH
looking for antibodies that inhibit hormone synthesis
see anti-TPOAb in 80-99% of cases
normal population has small % with anti-TPOAb

32
Q

hyperthyroidism primary & secondary

A

primary (thyroid gland) : increase in T3/T4 & decrease in TSH
secondary (pituitary): increased T3/T4 & TSH

33
Q

hypothyroidism primary & secondary

A

primary (thyroid gland): decreased T4 & increased TSH

secondary (pituitary): decreased T4 & TSH (example: prolactin tumor)

34
Q

causes of hyperthyroidism

A

excessive ingestion of hormone, leakage of hormone from storage, excessive hormone production:
graves’ disease, toxic adenoma or multinodular goiter

35
Q

lab testing for grave’s disease

A

increase in free T3/ T4
verrrry decreased TSH
increased TSI/ TSH receptor Ab
increased radioactive iodine uptake (RAIU) - scan shows diffuse pattern (!)

36
Q

grave’s treatment

A

surgery or use of radioactive iodine
medication is liver toxic (can cause aplastic anemia) & kill very active centers in the thyroid
monitor ALT, AST for liver function
remission: 20-50% in USA

37
Q

hypothyroidsim diseases

A

thyroiditis- hashimoto’s or viral subacute
congenital - cretinism
iodine deficiency

38
Q

symptoms of hypothyroidism

A 
low body temp, slow movement, weight gain (!), constipation
bradycardia, diastolic hypertension
menstrual irregularity
periorbital edema
congnitive dysfunction
39
Q

lab results for hashimoto’s

A 
increased TSH
decreased T4
decreased Na+ due to inappropriate ADH levels
increased CK due to myopathy
anemia/pernicious anemia
increased lipids
40
Q

Amiodarone

A

used for cardiac arrhythmias
is 37% iodine & can decrease thyroid hormone production
inhibits conversion of T4 to T3

Clinical Chemistry (23 decks)

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