Hypothyroidism
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Hypothyroidism
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USMLE® Step 1 style questions USMLE
of complete
| Laboratory value | Result |
| Sodium | 137 mEq/L |
| Potassium | 4.8 mEq/L |
| Chloride | 97 mEq/L |
| Glucose | 97 mEq/L |
| Creatine kinase (CK) | 145 U/L |
| Aspartate aminotransferase | 66 U/L |
| Alanine aminotransferase | 77 U/L |
Which of the following medications was this patient most likely taking?
Memory Anchors and Partner Content
External References
First Aid
2024
2023
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Amiodarone p. 327
hypothyroidism p. 248
hypothyroidism with p. 345
Autoimmune hypothyroidism p. 172
Fetal hypothyroidism p. 345
Goiter
maternal hypothyroidism from p. 345
Hypothyroidism p. 344, 345
amiodarone and p. 327
anemia p. 426
in anemia taxonomy p. 423
carpal tunnel syndrome and p. 452
as drug reaction p. 248
hormone replacement p. 360
lithium p. 592
Lithium p. 592
hypothyroidism p. 345
Pregnancy p. 651
hypothyroidism in p. 346
Sulfonamides p. 191
hypothyroidism p. 248
Transcript
Content Reviewers
In hypothyroidism, ‘hypo' refers to having too little, and ‘thyroid’ refers to thyroid hormone, so hypothyroidism refers to a condition where there’s a lack of thyroid hormones.
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, and 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.
Thyroid hormone is important - and the occasional increase can be really useful when you need a boost to get through the final rounds of a sporting competition or when you’re trying to stay warm during a snowstorm!
Now, hypothyroidism can happen a few different ways - and all of them result in a lack of thyroid hormones and a decreased basal metabolic rate, where cellular reactions are happening slower than normal.
Summary
Hypothyroidism refers to a condition where there's a lack of thyroid hormones (triiodothyronine (T3) and thyroxine (T4)), which normally help control the body's metabolism.
Hypothyroidism can be primary or secondary. In primary hypothyroidism, the thyroid gland isn't working properly, because of an autoimmune disease like Hashimoto's thyroiditis, hyperthyroidism treatment, or a congenital defect. In secondary hypothyroidism, either the anterior pituitary gland or the hypothalamus is the problem, usually because of a tumor or damage from surgery.
Symptoms of Hypothyroidism include weight gain, mental slowness, swelling in the skin and soft tissues, and a slower heart rate.
Sources
- "Robbins Basic Pathology" Elsevier (2017)
- "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
- "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
- "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
- "Harrison's Endocrinology, 4E" McGraw-Hill Education / Medical (2016)
- "Hypothyroidism" The Lancet (2017)
- "Hypothyroidism in Context: Where We’ve Been and Where We’re Going" Advances in Therapy (2019)
- "Hypothyroidism" The Lancet (2017)
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