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
