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54 Cards in this Set

  • Front
  • Back
T4 and T3 can dissociate from binding proteins instantaneously.
T4 and T3 enter cells by specific processes that are
Energy and Na+ dependent.
What mediate most of the physiological actions of the thyroid hormones?
Nuclear receptors(T3)
Nuclear receptor binds to
T3 more avidly.
In vivo,virtually all of nuclear bound hormone is
What are the 2 types of nuclear receptors?
-Alpha:3 forms
-Beta:2 forms
B1 receptors found in
Brain,kidney,liver and heart
B2 receptors found in
Pituitary and hypothalamus
Thyroid hormone RECEPTOR(TR) binds to
thryoid response element(TRE)
What happens after TR binds to TRE?
Stabilization by TRAP and transcription silencing by CoR.
What happens then when T3 binds to TR?
Formation of TR-T3 complex resulting in dissociation of CoR and recruitment of CoA.
Regulation of thyroid hormone production is via
Hypothalamic-pituitary-thyroid axis.
Thyrotrophin is also known as
Sequence of actions leading to T3/T4 release:-
TRH from hypothalamus--->TSH secretion from pituitary--->T4/T3 secretion(-ve feedback on hypothalamus and pituitary.
What regulates extrathyroidal conversion of T4 to T3?
Nutritional,hormonal and illness related factors.
Is TRH measurement useful clinically?
Not really measured except when given as injection to test ability of pituitary to produce TSH
TRH synthetized as
Large,pre-pro TRH protein in several tissues.
TRH is released from
Axon terminals close to hypo-pituitary portal plexus(which travel thru median eminence)
TRH producing neurons are densely innervated by
Catecholamines and Neuropeptide Y containing axons.(somatostain axon also involved)
TRH receptor is
G-protein coupled receptor with 7 transmembrane domains.
TRH binds to
Specific receptor in plasma mb of thyrotroph
heterodimer with alpha and beta subunits
Alpha subunit of TSH is
Common to those of FSH,LH and hCG.
What subunit of TSH confers specifity?
Normal bioactivity of TSH requires
TSH regulated by
TSH receptor is usually
A target of immune system.
What are the 2 forms of TSH receptor?
-Low affinity
-High affinity
Mediation of TSH actions
-activation of adenyl cyclase
-CAMP activates cAMP dependent kinases.
TSH actions?
-stimulates every step in thyroid hormone synthesis and secretion in thyroid.
-Stimulates intermediary metabolites.
-stimulates expression of many genes in thyroid tissues.
-causes thyroid hyperplasia and hypertrophy.
Signs and Symptoms of Graves disease:
-shaking arms,legs,hands
-weight loss
-sore eyes with blurry vision
-marked hunger
-extreme heat intolerance
On examination of pt with Graves?
-Thyroid diffusely enlarged with bilateral bruits.
-Obvious stare with lid retraction
-Brisk ankle jerks
Presence of which antibodies in Graves?
TSH receptor antibodies in higher levels.
Thyroid hormones levels in Graves/
High levels of T4 and T3 but low levels of TSH.
Thyroid stimulating Ab stimulates
Cells to produce T4/T3
What is hot nodule?
When Technecium injected in thyroid ,technecium accumulates where thyroid is working alot.-->black area.
High levels of hCG having TSH like effects can cause
hCG and TSH beta subunits have
considerable homology.
Hyperemesis gravidarum ?
Occurs during early pregnancy when hCG levels are high-->stimulate thyroid and increase T4 and T3.
Presentation of H.gravidarum?
-Severe vomiting
High hCG levels can also cause
Hydatidiform mole or choriocarcinoma.
Treatments for hyperthyroidism:-
-Ablative:either surgery or radioactive iodine.
Name 2 antithyroid drugs.
Effects of antithyroid drugs?
-Inhibit peroxidase system,preventing oxidation of trapped iodine & subsequent incorporation into iodotyrosines and ultimately iodothyronine.
-Inhibit coupling with iodotyrosines
-Inhibit conversion of T4 to T3 in peripheral tissues
-mild immunosuppressive effects
Antithyroid drugs bind to peroxidase at
Same site as iodide or nearby preventing binding of iodine.
What is resistance to thyroid hormones?
Inherited syndrome with reduced responsiveness of target tissue to thyroid hormone.
Where is the abnormality?
mutations in the Thyroid hormone Receptor-beta in T3 binding domain(101 mutations recognised)
What are the findings in this syndrome?
high T4 and T3 with normal or increased TSH.
Clinical features?
-Clinically euthyroid
-Goitre(due to high TSH)
-attention deficit disorder
-emotional disturbances
-recurrent ear and throat infections
-delayed bone age
-learning disability and retardation
-short stature.
Clinical findings with hypothyroidism due to pituitary failure?
-Low T4 and T3 + low TSH
-deteriorating eyesight
-feeling cold more than usual
weight gain,CONSTIPATION,dry skin.
What type of hypothyroidism is it ?
Secondary due to pituitary failure.
Somatostatin release from hypothalamus
Inhibits pituitary
Causes of hypothyroidism
-Central hypothyroidism:TSH/TRH deficiency:
-->pituitary tumour
--> pituitary surgery or radiation
--> infiltration-hypophysitis,hemochromatosis
-->infarction/apoplexy(sheehan syndrome)
-->CNS radiation
-->infiltrative lesions
Lab dx. of hypothyroidism
-total and free T4 decreased
-total and free T3 decreased
-TSH up(EXCEPT in central hypo. where it is normal or decreased)