The thyroid gland is part of the endocrine system. It is situated on the front part of the neck, against the trachea. The secretion of thyroid hormones is regulated by the pituitary gland. Thyroid dysfunction is common (hypertrophy (goiter), hyperthyroidism, hypothyroidism), causing variations in hormone secretion levels and a number of different pathological conditions. In the most severe cases, a thyroidectomy may be indicated.