Thyroid Pt 2 Flashcards
true or false: the thyroid stores lipid soluble hormone
true
how does the thyroid store hormone?
t3 and t4 are made on top of a protein on which it can be stored
benefit of the storage in the thyroid?
good as a reservoir if you’re having deficits in iodine or TSH
how long can the thyroid hormone be stored?
50 days
cons of storage in the thyroid?
if there’s some treatment that releases all the stored T3s and T4, you get thyroid storm (toxic)
effect of thyroid hormone?
stimulates the modulation of gene transcription by their receptors
- growth and development
- maintenance of BMR
which has greater transcriptional efficiency? T3 or T4?
T3
what kind of receptors bind thyroid hormone?
nuclear receptors
true or false: thyroid hormone receptors can only activate transcription
false, they can also inactivate transcription
does thyroid hormone act as a monomor, homodimer, or heterodimers?
all of the above
what’s RXR?
common heterodimer partner
what are the known genes that code for t3 and t4 receptors?
THRA (NR1A1) and THRB (NR1A2), both of which express different isoforms
what makes the different isoforms of the t3 and t4 receptors possible?
alternative splicing
where in the cell are thyroid hormone receptors?
- in the nucleus, typically already bound to the genome at their response elements
- in mitochondria too
how does thyroid hormone access its receptor?
entry by passive diffusion but can be aided by special transport systems
what happens when there’s too much T3?
localized cells can upregulate deiodinase enzymes to convert T3 to its inactive form, rT3
which receptor acts as an inhibitor
alpha 2 (a2)
which receptor is expressed more in the anterior pituitary?
beta 2 (b2)
examples of corepressors in the nucleus?
NCoR, SMRT
examples of coactivators in the nucleus
P160, SRCs, TRAP22
true or false: thyroid hormone has non-receptor activity
true: it can regulate the activity of proteins in the mitochondria (Cytochrome C and UCP-1)
what’s the name of the membrane receptor for TH?
aV and B3
chronotropic meaning
chrono = rate/timing
tropic = increase/grow
increased heart rate
inotropic meaning
increased force
the calorigenic action of TH entails what?
- increased O2 consumption
- increased heat production in metabolically active tissues
- fatty acid mobilization
- increased Na+/K+ ATPase activity
how does increased calorigenesis affect nitrogen excretion?
increased –> increases protein turnover, decreasing skeletal muscle
how does increased calorigenesis affect weight?
weight loss due to catabolism of fat and proteins
how does increased calorigenesis affect children?
positive nitrogen balance since T4 stimulates growth
how does increased calorigenesis affect carotene?
carotenemia
what’s myxedema?
T4 can activate protein metabolism, so lack of it can lead to an accumulation of these proteins. symptoms are puffiness of skin.
when there is an increased body temp, what is done to mitigate this?
- vasodilation in the extremities
- decrease in blood pressure that triggers electrolyte and water balance by the kidneys
- ultimately increases heart activity (force and heart rate)
effect of t3/t4 in the heart?
- increase a-myosin
- reduce expression of b-myosin filaments (weaker)
net result: increase heart rate and force
relationship between T3/4 and catecholamines?
have similar effects; they enhance each others’ sensitivity
true or false; blocking b-adrenergic receptors reduces activity of T3/T4
true
what’s a thyroid storm?
sudden increased secretion of stored T3/4 either because of sudden stimulus, infection, surgery, or trauma leading to dangerously increased effects. this is where b-adrenergic blockers come into play
true or false: nerves convert T4 to T3
false, they require the assistance of astrocytes
effect of TH on the nervous system?
increased responsiveness to catecholamines
lack of T3/T4 can lead to what disorder associated with the nervous system?
cretinism: stunted growth, mental retardation, motor rigidity, deaf-mutism
effect of increased TH on skeletal method
- hyperthyroidism: muscle weakness due to increased protein catabolism
- hypothyroid: muscle weakness, cramps, stiffness (too little growth)
exact mechanisms are still under study
effect of TH on CHO metabolism?
increase absorption of CHO by GI
effect of TH on cholesterol metabolism?
decrease cholesterol levels bc increased LDL receptors in liver
effect of TH on reproductive system?
female: follicular development and ovulation, maintenance of pregnancy
male: spermatogenesis
effect of TH in growth and tissue development?
- increase growth and maturation of bone (like GH)
- positive effect on epidermis (skin), hair follicles, and nails
- increased rate and force of skeletal muscle contraction
- inhibits synthesis and increases degradation of mucopolysaccharides in subcutaneous tissue
symptoms of hypothyroidism?
- fatigue
- coldness (cool, dry skin)
- weight gain
- constipation
- low voice
- swelling of face/hands/legs
- slow reflexes
- myxedema
children: retardation, short stature, swelling of face/hands, possible deafness
what are the types of hypothyroidism?
primary: thyroid gland failure (most common)
secondary: pituitary failure (TSH deficiency)
tertiary: hypothalamic failure (TRH deficiency; tissue resistance)
what’s levothyroxine?
synthetic T4.
what’s goiter?
condition due to iodine deficiency. less iodine leads to less production of T3 and T4, so less negative effect by the pituitary on TSH, which is a tropic hormone that increases growth of the thyroid gland.
hypothyroidism in the mother can carry over to the fetus leading to cretinism
how is goiter treated?
supplement with iodine
what’s thyropause?
increased susceptibility to hypothyroidism in the elderly. makes them more susceptible to winter conditions
what’s hashimoto’s disease?
autoimmune disease where it’s the major cause of hypothyroidism in areas with sufficient iodine. so you still get goiter even with enough iodine. no goiter in older patients
autoimmunity functions against TPO (iodination of TG) and/or TG
common cause of hyperthyroidism?
grave’s disease - autoimmune disease that produces anti-TSH receptor antibodies that elicits the same response as TSH. this leads to increased activity of the thyroid gland (increased growth, goiter symptoms, increased secretion of T3 and T4)
