control the rate of energy release (metabolic
rate), and disease results when they
malfunction. Excess storage of surplus energy
causes obesity, one of the most common diseases
of Western society.
hormones T3 and T4 are unique in that iodine (as
iodide) is an essential component of both. In
most parts of the world, iodine is a scarce
component of soil, and for that reason there is
little in food.
Thyroid hormones interact with intracellular
receptors, and it is this ligand-receptor
complex that directly provides the signal,
generally to specific genes whose rate of
transcription is thereby affected.