Endocrine System Health Article

Definition

The endocrine system is a widespread group of glands and organs that acts as the body's control system for producing, storing, and secreting chemical substances called hormones.

Description

The primary glands that compose the endocrine system are the hypothalamus, pituitary, thyroid, parathyroid, adrenal, pineal, ovary, and testes. The pancreas, considered both an organ and a gland, is also part of the system. The thymus is sometimes considered an endocrine-system organ. Although not part of the endocrine system, other organs that secrete hormones are the heart, brain, lungs, kidneys, liver, skin, and placenta. The word "endocrine" means that in response to specific stimuli, the hormones produced by the glands are released into the bloodstream.

Function

Hormones are compounds produced by the endocrine glands. They generally control the growth, development, and metabolism of the body; the electrolyte composition of body fluids; and reproduction. The specific functions of the endocrine glands and pancreas are unique.

Pituitary gland

The pituitary is the master gland of the endocrine system. Located at the base of the brain, the gland, which is about the size of a marble, consists of two parts: anterior and posterior. The anterior pituitary produces hormones that either stimulate other glands (such as adrenal, testis, ovary, and thyroid) to produce target-gland hormones, or directly affect the target organs.

Three of these hormones—adrenocorticotropic hormone (ACTH), gonadotropins, and thyroid-stimulating hormone (TSH)—act on other glands. ACTH stimulates the adrenal cortex to produce corticosteroid hormones and small amounts of male and female sex hormones. Gonadotropins are two hormones that regulate the production of male and female sex hormones and the egg (ova) and sperm (spermatozoa) cells. TSH stimulates the thyroid gland to produce and release thyroid hormone.

Another pituitary hormone, growth hormone (GH), has a central role in controlling the growth and development of the body and its components, including organs, tissue, and muscle. It also affects the metabolism of carbohydrates,

protein, and fat. For example, GH increases glucose levels in the blood by reducing the amount of glucose used by muscle cells and adipose tissue and by promoting glucose production from certain liver molecules. Other functions of GH include increasing the amount of amino acids that cells take from the blood and stimulating the breakdown of lipids (fats) in adipose tissue. The pituitary hormone prolactin acts with other hormones in female breast development and helps regulate breast-milk production (lactation).

Two hormones, vasopressin and oxytocin, are stored but not produced in the posterior pituitary. Vasopressin, also called arginine vasopressin (AVP), helps the body to conserve water by increasing reabsorption of water from the kidneys. Oxytocin stimulates contractions in the uterus during childbirth and activates milk injection caused by an infant sucking on the breast.

Adrenal glands

The adrenals are small glands on top of the kidneys. The adrenals have two parts: an outer layer called the cortex, and an inner layer called the medulla. The adrenal cortex produces a variety of hormones called corticosteroids, including hydrocortisone (cortisol), which helps increase blood glucose levels. It also reduces the amount of glucose absorbed by muscles and adipose tissue. Another function of cortisol is to protect the body from the adverse affects of stress, including emotional and physical trauma.

The adrenal medulla produces adrenaline and noradrenaline, substances that increase the heart rate and blood pressure during times of stress. Their action is referred to as the "fight-or-flight" response.

Thyroid gland

The thyroid gland is composed of two sections in front of the windpipe and below the voice box. It produces two hormones, thyroxine (T4) and tri-iodothyronine (T3), which together are called the thyroid hormones. They help regulate growth and development and help in childhood brain development. The thyroid also contains cells that produce the hormone calcitonin, which helps to maintain normal calcium levels in the blood.

Parathyroid glands

The parathyroid complex is composed of four small glands, each the size of a pea, and each located on the four corners of the thyroid gland. They secrete parathyroid hormone, which regulates calcium levels in the blood.

Pancreas

The pancreas is located in the upper abdomen, just behind and below the stomach. It has two functions: to produce various enzymes that aid in digestion; and to produce insulin and glucagon, hormones that are key to the body's management of glucose (sugar) in the blood.

The primary purpose of insulin is to lower blood-glucose levels in the body. It helps form glycogen, proteins, and lipids, which are stored in the body (usually in the liver, muscles, and adipose tissue) to be used for energy. Glucagon increases blood-glucose levels, an action opposite to that of insulin. A strict balance between the glucagon and insulin is required to maintain proper blood-sugar levels.