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Thyroid hormone
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Thyroid hormone is what sets the body's pace: it controls metabolism, that is, the speed at which energy is burned, along with growth and other functions. It comes in two main forms, thyroxine and triiodothyronine.
Its production is not left to chance. It is controlled by a loop that regulates itself, the hypothalamic-pituitary-thyroid axis: the hypothalamus, in the brain, releases thyrotropin-releasing hormone, and that hormone prompts the anterior pituitary, the gland that hangs below the brain, to release thyroid-stimulating hormone, the one that tells the thyroid to get to work.
Making the hormone takes iodine, an essential trace element, meaning the body needs very little of it but cannot do without it; it is absorbed in the small intestine and is part of both forms of the hormone. Once in the blood, the hormone does not travel free: it moves bound to carrier proteins. And when it reaches its destination it works like an order that changes what the nucleus commands, because it acts on nuclear receptors that switch on certain genes.
In brief
Thyroid hormone controls metabolism, growth and other functions; its main forms are thyroxine and triiodothyronine.
A self-regulating loop, the hypothalamic-pituitary-thyroid axis, controls it: the hypothalamus releases thyrotropin-releasing hormone and the anterior pituitary responds with thyroid-stimulating hormone.
Iodine, an essential trace element absorbed in the small intestine, is part of both forms; the hormone travels bound to carrier proteins and acts on nuclear receptors that switch on certain genes.
It is an order that comes in and changes what the nucleus commands.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Thyroid Hormone, StatPearlsPublished
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