The endocrine system consists of several glands that are located throughout the body. These glands secrete hormones or chemical messengers that signal the body to perform essential functions. These are usually related to growth and metabolism. These hormones are released directly into the bloodstream and travel throughout the body, affecting any cell that contains a receptor for the hormones. Their effect is widespread, slow and they are long-lasting. They regulate all types of bodily functions. They are controlled by the collaboration between hypothalamus and pituitary gland. An imbalance in these hormones causes disorders. The endocrine system consists of pineal gland, pituitary gland and hypothalamus, thyroid and parathoid gland, thymus, pancreas, adrenal glands, overing the female and testes or testicle in the male and placenta in the female during pregnancy. This brings us to the question how do hormones work? These hormones are involved in regulating all kinds of bodily functions. These hormones are controlled through the interaction between hypothalamus in central nervous system and the pituitary gland in the endocrine system. Hormones coordinate the physiology and behavior of an individual by regulating and integrating and controlling bodily functions. Another example of endocrine regulation of physiological and behavioral function is provided by pregnancy. Estrogens and progesterone concentrations are elevated during pregnancy. And these hormones are often involved in mediating maternal behavior in the mothers. We also need to understand that not all cells are influenced by each and every hormone. The hormone is effective only if there are specific receptors for that specific hormone. There must be a sufficient number of receptors available for a specific hormone to produce any effect. We must clearly understand that hormones do not cause behavioral change. They influence the three systems.