00:00 / 00:00
0 / 17 complete
0 / 9 complete
hyperthyroidism p. 348
amiodarone and p. 329
β -blockers in p. 247
choriocarcinomas p. 677
drug reactions p. 250
hCG elevation and p. 657
hydatidiform moles p. 663
mature cystic teratoma p. 671
osteoporosis p. 472
pulse pressure in p. 292
thionamides for p. 362
Normally, the hypothalamus, which is located at the base of the brain, detects low blood levels of thyroid hormones and releases thyrotropin-releasing hormone into the hypophyseal portal system - which is a network of capillaries linking the hypothalamus to the anterior pituitary.
The anterior pituitary then releases thyroid-stimulating hormone, also called thyrotropin or simply TSH.
TSH stimulates the thyroid gland which is a gland located in the neck that looks like two thumbs hooked together in the shape of a “V”.
The thyroid gland is made up of thousands of follicles, which are small spheres lined with follicular cells.
Follicular cells convert thyroglobulin, a protein found in follicles, into two iodine-containing hormones, triiodothyronine or T3, and thyroxine or T4.
Once released from the thyroid gland, these hormones enter the blood and bind to circulating plasma proteins.
Only a small amount of T3 and T4 will travel unbound in the blood, and these two hormones get picked up by nearly every cell in the body.
Once inside the cell T4 is mostly converted into T3, where it can exert its effect. T3 speeds up the cell’s basal metabolic rate.
It’s as if the cells are in a bit of frenzy.
T3 increases cardiac output, stimulates bone resorption - thinning out the bones, and activates the sympathetic nervous system, the part of the nervous system responsible for our ‘fight-or-flight’ response.
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