The endocrine system and the nervous system act individually and together for internal communication, messaging, control and regulation. The nervous system is made up of specialized cells called neurons, which convey high–speed electrical signals, where as endocrine system is a collection of all hormone secreting cells.

The signals communicated through neurons control the movement of body parts in response to sudden environmental changes, such as occur when you jerk your hand away from a hot pan or when your pupils dilate as you enter a dark room.

Hormones coordinate slower but longer–acting responses to stimuli such as stress, dehydration and low blood glucose levels. Hormones also regulate long–term developmental processes by informing different parts of the body how fast to grow or when to develop the characteristics that distinguish male from female or juvenile from adult. Hormone–secreting organs, called endocrine glands, are referred to as ductless glands because they secrete their chemical messengers directly into extracellular fluid and from there, these chemicals diffuse into the circulation through blood.