The living body possesses a remarkable communication system to coordinate its biological functions. This is achieved by two distinctly organized functional systems .

The nervous system coordinates the body functions through the transmission of electrochemical impulses.


·        The endocrine system acts through a wide range of chemical messenger known as hormones.
Hormones are conventionally defined as organic substances, produced in small amounts by specific tissues (endocrine glands),secreted into the blood stream to control the metabolic acid and biological activities in the target cells .Hormones may be regarded as the chemical messengers involved in the transmission of information from one tissue to another and from cell to cell. The major endocrine organs in body are controlled and regulated by hormones.

Classification of Hormones: 

Hormones may be classified in many ways based on their characteristics and functions. Based on the chemical nature the hormones can be categorized into three groups considering their chemical nature. They are protein, steroid and amino acid derivative hormones respectively.

Hypothalamic and Pituitary Hormones: 

The pituitary or hypophysis (weighing about 1g) is located below the hypothalamus of the brain It consists of two distinct parts-the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis) connected by pars intermedia. The later is almost absent in humans, although found in lower organisms.

Hypothalamus is a specialized center in the brain that functions as a master coordinator of hormonal action .In response to the stimulus of central nervous system, hypothalamus liberates certain releasing factors of hormones .These factors stimulate or inhibit the release of corresponding tropic hormones from the anterior pituitary. Tropic hormones stimulate the target endocrine tissues to secrete the hormones they synthesize. The relationship between hypothalamus and pituitary with endocrine gland is illustrated. For instance, adrenocorticotrophic hormone (ACTH) inhibits the release of corticotrophin releasing hormone (CRH).

Growth hormone: The growth hormone (or somatotropin) is produced by somatotropes, a special group of acidophilic cells of anterior pituitary.

Regulation of growth hormone release: Two hypothalamic factors play a prominent role in the release of growth hormones. These are the growth hormone –releasing hormone (GRH) that stimulates and the growth hormone is released. Growth hormone production is influenced by many factors such as sleep, stress (pain, cold, surgery),exercise food intake etc.

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