Thyroid

The thyroid sits at the front of the neck, wrapped around the windpipe just below the voice box in a shape early anatomists compared to a butterfly or a shield, which gave the gland its name. It draws iodine from the diet to manufacture two hormones, thyroxine and triiodothyronine, that set the pace of metabolism in nearly every tissue in the body, governing how fast cells burn energy, how the body regulates its own temperature, and how children grow. Too little of these hormones slows the whole system down, producing fatigue, weight gain and cold intolerance, while too much speeds it up toward rapid heartbeat, weight loss and heat intolerance. Because the gland depends on dietary iodine, a shortage of it was for centuries a leading cause of goiter, a visibly swollen thyroid straining to compensate, before iodized salt made the deficiency rare across most of the world.

Hatha yoga's subtle body reads the same throat as the seat of a different kind of output. In Swami Satyananda Saraswati's synthesis in Asana Pranayama Mudra Bandha, the thyroid correspondence sits with Vishuddha, the Throat chakra, the center the tradition reads as communication, self expression and the voice, the point where inner reality is said to be spoken into the world. The gland's location beneath the literal voice box gives the two accounts an unusually direct anatomical overlap, though the tradition's reading of that overlap is its own claim and not a finding the endocrine account makes.