Endo - Thyroid

Question 1

TH differences from amine hormones

Answer 1

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

Question 2

TH steps (broad)

Answer 2

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

Question 3

TH steps (specific)

Answer 3

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

Question 4

T4/T3 blood transport

Answer 4

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

Question 5

free vs bound Ts

Answer 5

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

Question 6

why is T3 active and T4 isn’t

Answer 6

T3 has higher affinity for receptor

T4 has high affinity or TBG

Question 7

key T3 actions

Answer 7

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

Question 8

how T3 ups CO

Answer 8

up HR and SV

up Ca ATPase activity, myosin ATPase and AC –> faster contraction and relaxation

Question 9

T3 permissive effects

Answer 9

E

NE

Question 10

neonatal hypothyroidism

Answer 10

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

Question 11

primary hypothyroidism

Answer 11

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

Question 12

secondary hypothyroidism

Answer 12

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

Question 13

iodide insufficiency

Answer 13

primary
T3/4 down
TSH up
possible goiter

Question 14

primary hyperthyroidism

Answer 14

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)

Question 15

secondary hyperthyroidism

Answer 15

excess TSH or TRH
T3/4 up
TSH up

Question 16

hypersecreting thyroid tumor

Answer 16

aka toxic adenoma
T3/4 up
TSH down