Endocrinology is a specialty that deals with the endocrine system, its related conditions, diseases, diagnosis as well as hormonal imbalances and disorders. The major endocrine glands are the thyroid and adrenal glands. They are responsible for the production of hormones essential for the body to function, and changes to any of them due to a disease or disorder can lead to hormonal imbalances. The endocrine system produces hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep and mood; and is very closely integrated with the neuroendocrine system. Diseases and conditions may arise when the organs and glands do not function as they should. They include diabetes, infertility, obesity and depression.