Eli Andretus, age 15 of Portland, Ore., for his question:
WHAT IS THE ENDOCRINE SYSTEM?
The endocrine system is made up of the associated organs and tissues of the body that collectively release substances known as hormones. Endocrine organs are known also as ductless glands because their secretions are released directly into the bloodstream, in contrast to exocrine glands, which discharge their secretions on such external or internal surface tissues as those of the skin, the lining of the stomach or the lining of the pancreatic ducts.
The endocrine glands and their hormones regulate the growth, development and function of certain tissues and coordinate many of the metabolic processes within the body.
Endocrinology is the study of the endocrine glands, the hormonal substances they produce, their physiological effects and the disorders and diseases that involve their malfunction.
The endocrine system includes the hypothalamus, the pituitary, the parathyroid, the thyroid, the pancreas, the adrenal, the ovary and the testes.
Each type of endocrine gland produces one or more hormones. The activity of the gland is controlled so that the proper amount of hormone is released at the proper time. The pituitary gland, which acts as a regulator, carries out much of this control. It is located at the base of the brain and had been called the master controlling gland of the body.
The hypothalamus must be considered an endocrine organ even though it is part of the base of the brain itself. It produces hormones that are needed by the body.
The thyroid gland, located in front of the windpipe, secretes hormones that regulate metabolism, the rate at which the body uses oxygen and food.
The parathyroid glands, located on the back surface of the thyroid gland, produce a hormone that regulates the way the body uses calcium and phosphorus.
The thymus, found in the chest cavity, stimulates the production of lymphocytes, white blood cells that fight infections.
The pancreas has cells that produce two hormones: glucagon and insulin. Glucagon acts on the liver, causing it to release stored sugar into the blood stream. Insulin helps blood sugar gain entrance to the body cells so that it can be used for energy.
There are two adrenal glands, one above each kidney. Each has two important parts: the medulla, or core, and the cortex, or outer portion. The medulla forms epinephrine, known also as Adrenalin, and norepinephrine. They help to stimulate the body when a person becomes very angry or frightened. The cortex produces many hormones that are needed by the body so that it can adjust to the stress of living.
The ovaries are the female sex glands. They produce hormones that make it possible for women to bear children.
The male sex glands are called testes. They produce a hormone that is responsible for stimulating the development of such male characteristics as the beard and the deep voice.