The endocrine system is a complex collection of hormone-producing glands that control basic body functions such as metabolism, growth, and sexual development. Many of the hormones produced by the endocrine glands interact with each other to maintain balance. The amount of hormones produced by each gland is carefully balanced.

Too much or too little of a certain hormone can have effects throughout the body and cause various endocrine disorders. Although many endocrine disorders that affect adults can affect children, the disorders may produce different symptoms in children.

Metabolism is the chemical activity that occurs in cells, releasing energy from nutrients or using energy to create other substances, such as proteins. The basal metabolic rate (BMR) is a measurement of energy required to keep the body functioning at rest. Measured in calories, metabolic rates increase with exertion, stress, fear, and illness.