Examples of endocrine signaling are hormones being secreted into the bloodstream. The endocrine glands which secrete hormones include: the pituitary gland, pancreas, thyroid, and gonads. The pituitary gland secretes growth hormone, which functions to encourage growth of cartilage cells and the skeleton. The pancreas secretes glucagon and insulin, which control the level of glucose into the blood. Somatostatin is another hormone that is also secreted by the pancreas which inhibits the release of glucagon and insulin. The primary hormones released by the thyroid are thyroxine (T4) and triiodothyronine (T3). These hormones have significant roles in regulation of weight, internal temperature, energy levels, and nail growth. The third hormone released by the thyroid gland is calcitonin, which is involved in calcium and bone metabolism. Calcitonin prevents the degradation of the bone, and it decreases the levels of calcium in the blood. Gonads are glands that secrete hormones involved in reproduction, like testosterone and estrogen. Sex hormones are vital for the development and function of reproductive structures.