The endocrine system is comprised of the glands and tissues that release hormones into the bloodstream, usually in response to a signal from the hypothalamus or pituitary gland. Hormones are synthesised, stored and secreted by the gland, and serve to regulate the function of distant organs or tissues. Hormone secretion occurs in response to a specific stimulus and is highly regulated, usually on several levels including the hypothalamus, the end organs and the gland itself. Hormones may have secondary effects that are not as tightly regulated, which at times may result in pathological states. For example, insulin is released in response to blood glucose concentration in a highly regulated manner, but the increased blood insulin needed to maintain euglycaemia in a horse with insulin dysregulation results in alterations in fat and protein metabolism. Thus, the result of chronic hyperinsulinaemia can be decreased fat mobilisation and increased adiposity.