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Flashcards in Thyroid gland Deck (40)
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1

thyroid anatomy

in the neck, bilobular form w/ central isthmus -'butterfly'
follicular cells & C cells

2

Follicular cells

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

3

C cells

make clacitonin

4

thyroid hormone precursor

tyrosine residue on the thyroglobulin

5

Iodine involvement in thyroid hormones

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

6

T3 2 base components

MIT + DIT

7

T4 2 base components

DIT + DIT

8

TSH stimulation on T3 & T4

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

9

MIT

3-monoiodiotyrosine
has one iodine in 3' position on ring

10

DIT

3,5-diiodotyrosine
has 2 iodines on 3' & 5' position on ring

11

biologically active thyroid hormone

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

12

regulation of thyroid

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

13

5'-deiodinase

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

14

type 1 5'-deiodinase

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

15

type 2 5'-deiodinase

located in brain & pituitary
keeps T3 constant level in the brain

16

type 3 5'-deiodinase

form deiodinates T3 to T2 & becomes completely inactive

17

transport of thyroid hormones

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

free T3 levels in the blood

0.4%

19

thyroid hormone cell action

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

thyroid hormones affect

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

21

thyroid effects

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

thyroid stimulating hormone TSH assay

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

23

serum total T4 or serum total T3 assay

RIA, chemiluminometric or immunometric

24

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

dialysis kit method

25

thyroglobulin assay

should not be in circulation bc they are in the thyroid
used to diagnose thyroid cancers

26

thyroid binding globulin TGB assay

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

27

thyroid stimulating antibody or TSAb or TSI

no TSH but thyroid TSH receptor is being activated by antibody

28

TSH receptor antibodies - TRAb or TSHR-Ab

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

29

Anti-thyroid peroxidase antibody or Anti-TPO Ab

attacks TPO which helps form thyroid hormones & process them

30

Graves disease general

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