Peds Thyroid issues Flashcards
In the endoplasmic reticulum, thyroglobulin molecules are produced, packaged in vesicles by the Golgi, and exocytosed into the lumen of the follicle and then Iodide (I − ) (from the diet) enters the follicle cell via basolateral :
Na + /I − cotransporters (the I‐trap)
In the follicular lumen, I − is oxidized to iodine by ______and substituted for H + on the benzene ring of tyrosine residues of thyroglobulin.
thyroid peroxidase
Binding of one iodine molecule will form monoiodotyrosine (MIT), and binding of two iodine moieties will form diiodotyrosine (DIT). This reaction is termed________. Thyroid peroxidase also catalyzes the binding of DIT to another DIT, forming T4. Some DIT will also bind to an MIT, forming T3. These products remain linked to the
organification
thyroglobulin (Tg).
The mature Tg, containing MIT, DIT, T4, and T3 (in order of greater to lesser abundance), is endocytosed back into the follicle cell and can be stored as______ until secreted
colloid
Proteolysis of the colloid is stimulated by____ and releases the constituent molecules. MIT and DIT reenters the synthetic pool, and T3 and T4 exit the basolateral membrane into the blood.
TSH
Most iodine in the diet is excreted into the urine without being taken up by the thyroid gland. Only about____% of ingested iodine is taken up by the thyroid. Of that, about ___ is organified; the other ¼ leaks out and winds up in the urine.
20
¾
Most of the _____ iodine is removed in the tissue and excreted in the urine. Only a very small percentage of the ingested iodine winds up in the stool (still in the organified state)
hormone‐associated
In the initial steady state, TBG is ____ saturated with T4.
As TBG concentration increases, causing more T4 to be bound, we see reducing of the_____ concentration. This stimulates___ secretion, which leads to an increase in the release of T4 from the thyroid
one‐third
free T4
TSH
*) T4 becomes redistributed between the bound and the free states, leading to a new steady state with the same free T4 concentration but an increased total T4.
Because T4 and T3 are bound >99% to TBG in plasma, the half‐life of T4 is ___ days and T3 is __ day. When making adjustments in LT4 therapy, it takes weeks to see a physiological effec
Congenital hypothyroidism
how common is it
gender preference?
Hypothyroidism present at birth is seen in 1/2000 to 1/4000 babies (Wisconsin 1/3350). It is most common in Hispanics and least common in African‐Americans. Girls are affected more often than boys (2:1).
The most common underlying reason of congenital hypothyroidism is__________seen in 75‐85% of cases. Most of these cases are sporadic (only 2% familial)
failure of the gland to form properly (absent, ectopic or dysplastic gland)
What causes Congenital hypothyroidism in 10% of the children?
About 10% of the cases are due to an enzyme defect in thyroid hormone synthesis (dyshormonogenesis) due to genetic defects (mostly autosomal recessive)
Worldwide, many cases are due to ______ but this is uncommon in developed countries (due to use of iodized salt).
iodine deficiency
About 5% of congenital hypothyroidism are cases are due to _______(lack of TSH secretion), mostly in association with other missing pituitary hormones.
central hypothyroidism
Is congenital hypothyroidism a lifelong disease?
sometimes, but sometimes not: about 10% of all newborns diagnosed, the hypothyroidism turns out to be transient (either due to late maturation of the thyroid axis or due to transient suppression by maternal antibodies).
