The endocrine system is made of glands and organs that produce and secrete hormones. Hormones are chemical signals that act as messengers between neighboring cells and distant sites in the body. Many hormones are secreted into the extracellular fluid and move through the circulatory system to reach their target. However, they can only affect cells with receptors for a given hormone. The endocrine system regulates many biological processes through these signals, including metabolism, reproduction, and development. The endocrine and nervous systems mediate intercellular communication and work together to maintain homeostasis, but each has a specific time frame and means of relaying information. Nerve impulses travel quickly through the body through electrical signals and the release of neurotransmitters but stop their effect immediately after removing a stimulus. A person will quickly notice a hot object but will no longer feel the heat after removing their hand. Some hormones can trigger rapid responses, like adrenaline, in fight-or-flight situations. Others initiate long-term signaling, such as reproductive hormones, that have an effect even after their removal.