Animals have two systems of internal communication and regulation: the nervous system and the endocrine system. They both act individually and together to regulate an animals physiology.
Made up of the hormone-secreting cells
Hormones direct slower but longer-acting responses to stimuli such as stress and dehydration
Coveys high-speed electrical signals along neurons
Neural signals control the movements of body parts in response to sudden environmental changes
The nervous and endocrine systems overlap to some extent. For example, the nervous system plays a role in certain sustained responsescontrolling day/night cycles and reproductive cycles in many animals, for exampleoften by increasing or decreasing secretions from endocrine glands.
The fundamental concepts of biological control systems are important in regulation by hormones. A receptor, or sensor, detects a stimulus and sends information to a control center. After comparing the incoming information to a set point, the control center sends out a signal that directs an effector to respond. In endocrine and neuroendocrine pathways, this outgoing signal, called an efferent system, is a hormone or neurohormone, which acts on particular effector tissues and elicits specific physiological or developmental changes. The three types of simple hormonal pathwayssimple endocrine pathway, simple neurohormone pathway, and simple neuroendocrine pathwayinclude these basic functional components.
In a simple endocrine pathway, a stimulus informs a receptor protein of a change in an internal or external variable, which then alerts an endocrine cell which releases a hormone into the bloodstream as an efferent signal that elicits a response from the target effectors.
A common feature of control pathways is a feedback loop connecting the response to the initial stimulussuch as negative feedback, in which the effector response reduces the initial stimulus, and eventually the response ceases. Our own body temperature is kept close to a set point of 37°C by the cooperation of several negative-feedback circuits that regulate energy exchange with the environment: