With Riedel’s thyroiditis, thyroid- refers to the thyroid gland, and -itis means inflammation. So, Riedel’s thyroiditis is a condition where there is inflammation of the thyroid gland, which slowly causes fibrous tissue to replace the normal thyroid tissue. The condition is named after the German surgeon - Dr. Bernhard Moritz Carl Ludwig Riedel - who first described it.
Normally, the hypothalamus, which is located at the base of the brain, secretes thyrotropin-releasing hormone, known as ΤRH, into the hypophyseal portal system - which is a network of capillaries linking the hypothalamus to the anterior pituitary gland. The anterior pituitary then releases a hormone of its own, called thyroid-stimulating hormone, 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”. If we zoom into the thyroid gland, we’ll find thousands of follicles, which are small, hollow spheres whose walls are lined with follicular cells and are separated by a small amount of connective tissue. 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, but 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 then it can exert its effect. T3 speeds up the basal metabolic rate. So as an example, they might produce more proteins and burn up more energy in the form of fats and sugars. It’s as if the cells are in a bit of a 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.