The thyroid is an endocrine gland located in the front of the neck.
The thyroid gland secretes about 3 parts of thyroxin (T4, or tetraiodothyronine) to one part of triiodothyronoine (T3), and this allows the liver to regulate thyroid function by converting more of the T4 to the active T3 when there is an abundance of energy.
The thyroid also secretes calcitonin.
The thyroid responds to stimulation from the pituitary hormone thyrotropin, also known as thyroid-stimulating hormone (TSH).
Thyroid function correlates with the basal metabolic rate.
In the 1930s, it was standard medical practice to have a little apparatus to allow the person to lie down, usually with an empty stomach, and to breathe oxygen for two minutes, and they would measure how much oxygen was used. And people who had the standard symptoms of low thyroid function would often consume only half the normal amount of oxygen in the allotted time.
Thyroid function can be assessed with the Achilles reflex test. Delayed relaxation of deep tendon reflexes (Woltman sign) is often seen in hypothyroidism.
Hypothyroidism causes cholesterol to increase.
Hypothyroidism causes the thymus gland to atrophy.
Hypothyroidism reduces the function of the liver, causing estrogen to increase.