FUNCTIONS OF HORMONES

The secretory products of endocrine glands are hormones. Traditionally a hormone is defined as a substance that is produced in minute amounts by a collection of cells, is secreted into the interstitial spaces, enters the circulatory system on which it is transported some distance, and acts on specific tissues called target tissues at another site in the body to influence the tissues' activity.

The hormones produced by the pancreas enable the body to break down (metabolize) the food you eat. They regulate the body's use of glucose, a simple form of sugar that is an energy source for much of the daily activities of all human cells. Three hormones are produced by the pancreas. The first is insulin, which is produced when the concentration of glucose in the blood increases. This normally occurs shortly after a person eats a meal. Muscle and fat cells are stimulated by insulin to absorb the glucose they need as fuel for their activities. The second pancreatic hormone is glucagon. When needed, it breaks down the glycogen stored as fuel into the bloodstream. In effect, this raises the concentration of sugar in the blood. The third hormone produced by the pancreas, somatostatin, is a factor in regulating the production and release of both insulin and glucagon.

When secreted into the bloodstream adrenal medulla hormones increase cardiac output, blood flow to skeletal muscles and heart, and release of glucose and fatty acids into blood. The cortex produces a group of hormones called corticosteroids, of which there are three kinds. One kind is the sex hormones. They affect sexual development and reproduction. Another kind includes glucocorticoids. They influence the conversion of starchy foods into glycogen in the liver. The third kind is the mineralocorticosteroids. They control the body's use of minerals, sodium and potassium. The hormones of the adrenal gland affect virtually every system in the human body to some degree.

The thyroid gland helps set the rate at which the body functions. It responds to instructions from the pituitary gland to secreting the hormone thyroxine, whose actions control the rate of chemical activity in the body. Such activities vary directly with the quantity of thyroxine present: the more hormones circulating in the bloodstream, the greater the speed at which chemical reactions occur.

As you know the pituitary gland (hypophysis) consists of two parts, the front (anterior) lobe and the posterior lobe. The anterior lobe produces six distinct hormones, including prolactin to stimulate the production of breast milk and growth hormone to regulate the body's physical growth. The other four hormones influence other parts of the endocrine system, stimulating activities in the thyroid gland, ovaries, testicles, and adrenal glands. The posterior lobe produces two hormones: oxytocin and antidiuretic hormone. Oxytocin prompts contractions during childbirth and stimulates the breast to release milk during breastfeeding. Antidiuretic hormone acts on the kidneys to control urine output.