Thyroid Gland Flashcards
Structure
Follicle
sphere of
T3/T4
TG (binding protein)
Parafollicular cells aka, location
secretes
functional unit, secretes 2 hormones & binding protein
cells filled w colloid
Tri-iodothyronine, tetra-iodothyronine (thyroxine)
Thyroglobulin
C cells, outside follice
calcitonin
Thyroid hormone synthesized from
requires
Iodide trapping is an _____
normal thyroid: serum conc gradient
Also occurs in
Competitively inhibited by
results in
2 tyrosine residues attached to TG molecules in follicle lumen
iodine
active trasport process of NaI symporter
30:1 (can be up to 400:1)
Kidney, salivary gland, intestinal mucosa, mammary gland, placenta
other anions (goitrogens) such as perchlorate/Thiocyanate
dec iodide uptake
Thyroid hormone helps to
_____ of iodide after transport to lumen, creating I2
TG is then _______
catalzed by
synthesize/exocytose TG
oxidation
iodinated on tyrosine residues
thyroperoxidase (TPO)
Thyroid gland fxn controlled by
____ of iodine, forms ___ via TPO
Coupling of MIT/DIT leads to
stored in ______ w TG forming ______
TSH
organification, MIT/DIT
formation of T4 and T3, 10:1 ratio
lumen
colloid
In response to TSH
____ of TG
____ of colloid droplets with lysomomes, ____ of TG
_____ t3 and T4
_____ of MIT/DIT
AA are then ______ for TG synthesis
Iodine is ______
Secretion
endocytosis
fusion, hydrolysis
release
deiodination
re-used
recylced, providing 2x more of NaI symporter
Thyroid hormones in plasma
over 99% is _____ bc they are poorly solubilized
Most is bound to ______ synthesized by
Remainder bound to
Some T4 is weakly bound to
bound to plasma proteins
TBG, liver
albumin
TBPA or TTR
T3 vs T4
_____ together, more? plasma conc?
TBG binds __ more tightly
T3 is
Half lives
Interconversion, in serum
in target tissues, DIOs convert
DIO1
DIO2
DIO3 location
T4 is precursor to
T4 is _____ at physio levels, binding to receptors w
released, more T4
T4
faster acting, more potent
T3=2days, T4=&7 days
1/3 of T3 comes from T4
T4 to T3 when it enters cell
thyroid, liver, kidney
brain, PG, thyroid, placenta, muscle (necessary for NF and IC T3 levels)
Brain, placenta, skin (inactivates T3/T4)
T3
inactive, less affinity
CNS controls will ___ TRH and TSH synthesis/secretion
such as
TSH ____ fxns of gland
___ hyperplasia, results in
___ bloodflow
____biosynthetic pathway
_____T3/T4 synth, sec
Actions on other tissues
T3/T4 exert ____ on TRH/TSH
inc
temp, stress (dec TSH), diurnal rhythm
inc all
inc, goiter/enlarged gland
inc
inc
inc
direct actions
NFA
Thyroid hormones
effects are
Have both ___ and ___ effects
Affects ___ of cells
Multiple receptor ___, such as
Unoccupied thyroid hormone nuclear receptors are _____, resulting in
hormone binding leads to
enter cells via _____
such as
time course, duration
not essential for life, but for quality of life
diffuse, all tissues express TH receptors
genomic (gene trxn via nuclear receptors) and nongenomic
metabolism
isoforms, TRA1, TRB1, TRB2
bound to DNA to repress trxn
initiates modulation of gene trxn
membrane transporters
OAT1C1 (T4), MCT8 (T3)
Slow, prolonged
Calorigenic/thermogenic effect of TH
____ BMR
____ O2 consumption, heat production and fuel metabolism
deficiency leads to
excess leads to
inc
inc
hypothyroid, low BMR, cold, dec appetite
hyperT, high BMR, heat, inc appetite/catabolism
Sympathomimetic effect
_____ B adrenergic receptors, mimics activation
B blocking drugs (propanolol) will
Important in ___ in fetus/infant
deficiency results from
leads to
to avoid cretinism, administer ____ w/in 3 wks
inc, of SNS
inhibit sx of hyperT, exacerbates hypoT
CNS maturation
decreased uptake of iodide in pregnancy/neonatal life
mental retard, stunted growth (cretinism)
TH
TH needed for _____, esp alertness/reflexes
important for ____
esp ___, indirect effect on
can affect
deficiency in kids leads to
normal reactions, inc CNS conduction velocity, irritability of neurons
normal growth
GH syn/sec, bone formation
bone maturation/age
short stature, retarded bone age
TH and fuel metabolism
INC glcusoe ______, as well as
inc ____, leading to dec
inc ___ at normal levels, inc ____ at high levels
CV effect
Calorigenic effect
Repro system
essential for
excess/defic can lead to
absorption/oxidation, glycogenolysis/gluceoneogenesis
lipolysis, dec serum cholesterol
protein synth, protein catabolism
HR/contractility/CO
inc heat load, leading to VD and dec TPR, ultimately inc CO
normal fxn in both sexes
dec fertility
primary HypoT caused by
lab values, due to
potential etiologies
secondary to dec pituitary fxn
tertiarty to dec CNS fxn
Iodine def lab values
Rare potential cause
dec Thyroid gland fxn
dec T3/T4, inc TSH due to lost NFM of T3/T4
destroyed gland, Ca, irritation, thyroiditis, enzyme defect, anithyroid drug, AI (Hashimoto)
dec TSH, dec T3/T4
Dec TRH/TSH/T3/T4
Dec I, dec T3/T4, inc TSH
thyroid hormone receptor defect
HypoT
Sx in adults
S, W, dec H/G, dec L/F, M, G
Somnolence, weakness, dec HR, GI motility (const), dec libido/fertility, myxedema (SubQ deposit of mucopolysaccharide in eyelids/finger/lips), Goiter (high TSH)
