The illustration shows the thyroid gland with its two lobes and connecting isthmus. The thyroid gland produces hormones that have an effect on growth and metabolism. The parafollicular cells inside the basal membrane produce calcitonin, which lowers the blood`s calcium level. The thyroid gland also stores and releases the hormones thyroxin (T3) and triiodothyronine. These hormones regulate the metabolism of carbohydrates, fat, and proteins, the physical and mental development, and the water balance. A controlling mechanism is the negative feedback loop between thyroid gland, pituitary gland, and hypothalamus.