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Endocrine system




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A 50-year-old woman comes to the clinic due to insomnia and anxiety over the past few months. The patient’s last menstrual period was 1 year ago, but she denies hot flashes or vaginal dryness. The patient notes that her hair has become fine lately, and she has been losing weight without intention. On physical examination, a non-tender, diffuse goiter is noted. Laboratory tests show low TSH and high free T3 and T4 serum levels. The physician suspects that the patient’s condition is due to the most common cause of hyperthyroidism. Which of the following is the most specific finding for this condition?

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Graves disease

hyperthyroidism p. 348

Hyperthyroidism p. 346, 348, 671

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


In hyperthyroidism, ‘hyper’ refers to having too much, and ‘thyroid’ refers to thyroid hormone, so hyperthyroidism refers to a condition where there’s excess thyroid hormones.

The condition is also called thyrotoxicosis, and is generally due to overproduction from the thyroid gland.

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.

So as an example, the cell might produce more proteins and burn up more energy in the form of sugars and fats.

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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  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Harrison's Endocrinology, 4E" McGraw-Hill Education / Medical (2016)
  6. "Hyperthyroidism" The Lancet (2016)
  7. "Hypothyroidism and hyperthyroidism" Acta Bio Medica Atenei Parmensis (2019)

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