Introduction to Endocrine System

The endocrine system is a collection of ductless glands that secrete chemical messages, known as hormones.

The role of the endocrine system is to maintain homeostasis and long-term control of the human body using chemical signals (the hormones).  Also, the endocrine system works in parallel with the nervous system to control growth and maturation along with body homeostasis.The hormones produced by the glands of the endocrine system are passed through the blood circulation to arrive at a target organ, which possesses a series of cells that bear an appropriate hormone receptor. This receptor binds with the hormone molecule and triggers a series of chemical reactions inside the cell.  As mentioned before, the endocrine system is constituted by the endocrine glands – which secrete hormones.

The major endocrine glands include:

• the hypothalamus
• the pituitary gland
• the thyroid gland
• the pancreas
• the adrenal glands
• the gonads or sex organs

 

HORMONES

A hormone is a messenger molecule synthesized and secreted by a group of specialized cells that constitute an endocrine gland. These glands are ductless, which means that their secretions (hormones) are released directly into the bloodstream and travel elsewhere in the body to target organs, upon which they act. Note that this is in contrast to the exocrine glands, which have ducts for releasing the substances that they produce. Exocrine glands (not part of the endocrine system) secrete products that are passed outside the body. Sweat glands and salivary glands are examples of exocrine glands.

There are three general groups of hormones. These are classified as follows – according to their chemical structure:

• Steroid hormones including prostaglandins which function especially in a variety of female functions and the sex hormones all of which are lipids made from cholesterol.
• Amino acid derivatives (like epinephrine) which are derived from amino acids, especially tyrosine.
• Peptide hormones (like insulin) which are the most numerous/diverse group of hormones.