Each human body is composed of billions upon billions of cells; more cells than there are people in the whole world. Each cell has thousands upon thousands of simultaneous activities happening at the edge of dynamic order and chaos. Keeping them in working cooperation would certainly require executive orders called hormones, which may be steroids, polypeptides, or amines. These make sure every part of the body is doing its share, no more and no less. They also regulate and organize enzyme production and distribution. Hormones are produced by various organs called glands. Some produce fluids that pass thru systems of little tubes called ducts while others pass fluids thru thin membranes and the hormones directly enter the bloodstream, carrying them to all parts of the body. These are classified as endocrine (ductless) and exocrine (duct) glands. Like muscles, both endocrine and exocrine glands are biological effectors that respond to stimulations by nerve impulses and bring about body’s responses and effect body’s changes.

There are 9 major endocrine glands. Not in any particular order, these are (1) hypothalamus, (2) pituitary, (3) thyroid, (4) parathyroid, (5) pancreas, (6) adrenal, (7) gonads, ( pineal, and (9) thymus. Among them only the pancreas secretes both duct digestive fluids and ductless hormones. The pituitary is the CEO while the hypothalamus is the board of director of hormone production and distribution. It regulates blood temperature, monitors chemical compositions, and other metabolic functions. It also controls heart rate, breathing rate, blood pressure, and sleep patterns. Surgical removal of some glands such as the parathyroid or the adrenal would mean instant death while removal of one lung, one kidney, or the whole stomach can still keep the body alive but not at its maximum healthful conditions. The working of hormones is still much of a mystery. They are much less understood than enzymes or vitamins. However, it is known that one of the most important protein hormones of the pituitary gland is so small that it consists of only 8 amino acids strung together representing the 8 properties of directional invariance.