Endocrinology is the diagnosis and treatment of endocrine diseases. The endocrine glands secrete hormones - natural chemicals that enter the bloodstream and affect all bodily functions. Major endocrine glands include the pituitary, thyroid, adrenals, pancreas, ovaries and testes. Hormones regulate reproduction, growth and development, responses to stress, activity levels, blood circulation, metabolism, appetite, thirst, digestion and excretion. Endocrinologists treat a correspondingly wide variety of disorders, including diabetes, hyperthyroidism or hypothyroidism, infertility, growth hormone deficiency, genetic dysfunction, hormonal imbalances, osteoporosis, obesity and glandular cancers. An endocrinologist may practice general endocrinology or subspecialize, with particular expertise in disorders of one or two glands.