The endocrine system is an intricate "feedback" system, in which hormones release or suppress other hormones, controlling the way the body works. Balance is crucial, because an unhealthy component (gland) could cause repercussions to cascade down into all parts of the body. For example, an unhealthy pituitary can produce too much growth hormone (leading possibly to giantism) or too little, which can lead to premature aging and wasting of tissue.
The hypothalamus gland produces a releasing factor known as thyroid stimulation hormone releasing factor, or TSH-RF. It is a secretion of the brain that controls the pituitary gland. It regulates survival processes, such as reproduction, nourishment, and self-defense, by initiating the appropriate physical response through nerve impulses and chemical messengers.
The pituitary, which is controlled by the hypothalamus, has two distinct parts, the anterior and posterior lobes. Each one releases different hormones. The hypothalamus is and essential link between the brain and the pituitary. For example, the hypothalamus releases hormones stored in the posterior pituitary, including: oxytocin, vital in childbirth and nursing, and vasopressin, the water-regulating hormone; it also releases "turn on" hormones form the anterior pituitary, which stimulates secretions by other endocrine glands.
The pineal gland works in harmony with the hypothalamus gland, directing the body's thirst, hunger, sexual desire and the biological clock that determines our aging process. It is the "third eye" of the brain, responsible for telling the brain when it is day or night. It also controls the body's hormonal systems, sleep-wake cycle, and other so-called "circadian" (24-hour) body rhythms. It is in essence, the body's internal clock.
Various functions and rhythms of the human body are controlled by hormones which might be defined as chemical messengers. Most of these hormones are produced by these and the other major endocrine glands, but several other organs also manufacture hormones – the stomach, liver, intestines, kidneys, and heart all contain groups of hormone-secreting cells.