Endo - Thyroid Flashcards Preview

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Flashcards in Endo - Thyroid Deck (16):
1

TH differences from amine hormones

no rapid synth
not stored in granules
not water soluble
no short half life
no membrane receptor

2

TH steps (broad)

1. uptake/conc of iodide
2. ox and incorporation of I into phenol ring of tyrosine
3. coupling of 2 iodinated tyrosine molecules to make T3 or T4

3

TH steps (specific)

1. iodide comes into follicular cell (w/ Na) via NIS (I trap)
2. thyroglobulin made from tyrosine in rER, vesicle-d in golgi and exocytosed into lumen
3. iodide goes into lumen via pendrin
4. thyroid peroxidase combines thyroglobulin + iodide --> MIT, DIT --> T3, T4
5. all go back into cell via megalin
6. lysosome hydrolyze Tg, MIT/DIT are deiodinated and recycled
7. T3 and T4 are released into blood

4

T4/T3 blood transport

70% bound to thyroxine-binding globulin
29.5% bound to prealbumin/albumin
rest is free (available for activity)

5

free vs bound Ts

if free drops, bound releases
if more TGB, free will bind and thyroid will compensate
must look at free for Dx

6

why is T3 active and T4 isn't

T3 has higher affinity for receptor
T4 has high affinity or TBG

7

key T3 actions

up BMR
up mito
up FA use
up Na/K ATPase
up CO
bone development/growth
CNS maturation

8

how T3 ups CO

up HR and SV
(up Ca ATPase activity, myosin ATPase and AC --> faster contraction and relaxation)

9

T3 permissive effects

E
NE

10

neonatal hypothyroidism

inpaired brain growth
inpaired axon proliferation/myelinization
need to treat immediately after birth
sx: short, malformed legs, intellectual disabilities, delayed puberty, muscle weakness

11

primary hypothyroidism

thyroid failure
Hashimoto's - most common cause
autoimmune, thyroid Abs damage thyroid
T3/4 down
TSH up
possible goiter

12

secondary hypothyroidism

pituitary/hypothalamus failure
T3/4 down
TSH down
no goiter
problem is not enough TSH

13

iodide insufficiency

primary
T3/4 down
TSH up
possible goiter

14

primary hyperthyroidism

prob in thyroid
Grave's disease
thyroid stimulating immunoglobulins (autoimmune - Ab target thyroid receptor - stim synth - act like TSH)
T3/4 up
TSH down (feedback in tact)

15

secondary hyperthyroidism

excess TSH or TRH
T3/4 up
TSH up

16

hypersecreting thyroid tumor

aka toxic adenoma
T3/4 up
TSH down