Hormones are chemical messengers that are secreted by endocrine glands. These messengers may be lipophilic or hydrophilic (nonpolar or polar molecules, respectively). Hormones are stable enough to travel great distances without being degraded in the body. Because of their ability to travel great distances on occasion, they are target specific. That is, for example, a hormone may have its receptor at only one target tissue location. This specificity prevents the presence of the hormone from unintentionally activating or inhibiting processes on its journey throughout the body.

The adrenal glands, which lie on top of the kidneys, are responsible for releasing epinephrine and norepinephrine—both hormones that are present in the "fight or flight" response. These hormones are responsible for the increase in blood pressure, blood sugar, and heart rate. In a simpler sense, they help produce the means and conditions necessary to generate a surge of energy for quick expenditure in times of impending peril. 

The pituitary gland is also known as the “master gland” and is controlled by the hypothalamus. It is a crucial component of the endocrine system. The pituitary gland is responsible for the release of growth hormone, which stimulates physical development. It also releases oxytocin, allowing for contractions during birth and milk flow for nursing. The pituitary secretes oxytocin during pair-bonding interactions; therefore, the pituitary gland also plays an important role in the development of group cohesion and social trust. Last, the pituitary gland is also known to give secretions that will stimulate the release of hormones in other endocrine glands. 

The hypothalamus is responsible for control of hunger, thirst, body temperature, and the endocrine system. A person experiencing issues associated with the expression and regulation of the endocrine system would most likely have an issue associated with their hypothalamus.

The pituitary gland activates other glands in the endocrine system by releasing hormones. It also releases hormones that are resonsible for growth; sometimes the pituitary gland is known as the "master gland". 

The adrenal glands secrete the hormones epinephrine and norepinephrine to trigger the "fight-or-flight" response that helps the body in times of distress.

Alzheimer's disease is cause by low levels of Acetylcholine in some parts of the brain. This neurotransmitter is responsible for alertness, aggression, and other emotions.

Acetylcholine is a neurotransmitter that helps the brain retain newly learned information. It also aids in the control of the heart’s beat rate.

This called the HPA axis, which is a neuroendocrine system in the body that responds to stress and releases cortisol.

Hormones, or chemicals released by the endocrine system into the bloodstream for delivery throughout the body, have a much longer lifespan than neurotransmitters, and induce changes to body systems that last for hours, days, or which can even be permanent.