Endocrinology studies the physiology and pathology of endocrine glands. Endocrine glands produce hormones that sustain metabolism, control sexual secondary characteristics, regulate temperature, influence behaviour, personality and mood, and many other physiological functions. Amongst most organs in the body, endocrine glands are probably the most important in relation to body shape and the quality of tissues. For example a low function of the thyroid during development, due to lack of oligo elements or essential nutrients could influence the phenotype by changing its expression independently from the genetic makeup. And the production and levels of hormones can significantly influence our thoughts, actions and behaviours.