Biochemical messengers are molecules that transmit signals within and between cells, playing a crucial role in regulating various biological processes. These messengers include hormones, neurotransmitters, and cytokines, which help coordinate functions such as growth, metabolism, and immune responses. They bind to specific receptors on target cells, triggering a response that can alter cell behavior. Hormones, like insulin and adrenaline, are examples of biochemical messengers produced by glands in the endocrine system. Neurotransmitters, such as serotonin and dopamine, facilitate communication between nerve cells in the nervous system. Together, these messengers ensure that the body responds appropriately to internal and external stimuli.