ENDOCRINE SYSTEM

The endocrine system consists of cells, tissues, and organs that produce hormones or other chemical substances. The organs of endocrine system act together to control body activities and maintain homeostasis. In most people, the pancreas, the adrenal, pituitary, thyroid, and parathyroid glands, and ovaries or testicles work in tandem. The endocrine system regulates various functions of a human organism. It functions as a control system for the human body. Unlike other organs and body parts that enable to move, breathe, eat,

or sense the world around us, the endocrine system influences the body's processes. Along with nervous system, it coordinates the body's activities and responses to usual and unusual events.

Although both the endocrine system and the nervous system regulate the activities of structures in the body, they do so in different ways. These two systems cannot be separated completely either anatomically or functionally. For example, some hormones secreted by endocrine glands affect the nervous system and markedly influence its activity.

The key mechanism of the endocrine system is the hormone. Different types of endocrine hormones are secreted by different glands (pituitary gland, thyroid gland, parathyroid glands, pancreas, adrenal glands, gonads: ovaries and testicles, pineal gland, and thymus gland). Most of these hormones are released into the bloodstream so that they can deliver instructions to various organs and tissues. The pancreas, for example, secretes the insulin hormone, which enables the body to regulate the amount of sugar in the bloodstream. In response to stress or other stimuli, the adrenal glands secrete adrenaline, which produces a sudden and remarkable burst of energy.

Similarly, the pituitary, thyroid, parathyroid, and gonadal glands influence certain body functions. Glands, which send the chemical substances into ducts leading to external body surfaces, are called exocrine glands. They are mammary, salivary, lacrimal and sweat glands.

A hormone is an organic substance with a special molecular structure secreted by definite cells that has an effect on the function of another cells. Although hormones circulate throughout the body via the bloodstream, each hormone influences on only certain organs (target organs) or tissues. So, several types of chemicals are produced by cells and act as chemical messengers, but not all of them are hormones.

Hormones are proteins, glycoproteins, polypeptides, derivatives of amino acids, or lipids (steroids or derivatives of fatty acids).

As a rule, the greater the amount of a particular hormone in the bloodstream, the greater activity of the target organ. Some hormones (such as several of those produced by the pituitary gland) control other glandular activity, but virtually every system in the body is subject to the influence of the hormones, either directly or indirectly.