The endocrine system is made up of glands that secrete hormones directly into the bloodstream to regulate bodily functions. The major glands include the pituitary, thyroid, adrenals, ovaries and testes. Hormones control mood, growth, tissue function and metabolism. Endocrinology is the study of endocrine gland disorders. While endocrine glands are ductless, other organs like the kidneys and liver have secondary endocrine roles by secreting hormones.