Endocrinology is the study of hormones. Hormones are essential for our every-day survival. They control our temperature, sleep, mood, stress, growth and more. Hormones are found in all organisms with more than one cell, and so they are found in plants and animals. They influence or control a wide range of physiological activities, such as growth, development, puberty, level of alertness, sugar regulation and appetite, bone growth, etc. You also find that problems with hormones and the way they work contribute to some of the major diseases of mankind; for example, diabetes, thyroid conditions, pituitary conditions, some sexual problems, some neurological problems, appetite and obesity, bone problems, cancer, etc.