The endocrine system

The endocrine system is a series of glands that works with the nervous system to maintain homeostasis in the body.  Each gland secretes specific hormones that pass through the blood to the appropriate receptors on specific organs.  The endocrine system uses negative feedback and cycles for regulation.

The main glands of the endocrine system are the pituitary gland, the hypothalamus, the pancreas, the thyroid gland, and the adrenal glands.  The pituitary gland is linked to the hypothalamus to control release of pituitary hormones from the anterior pituitary lobe.  The hypothalamus monitors levels of thyroid and growth hormones in the blood.  The thyroid is located in the neck and controls metabolic rate, regulates growth and development, and regulates the onset of maturity.   Thyroid hormones target almost all body cells (Farabee, 2001).  The pancreas secretes insulin and glucagon.   The adrenal glands are located at the top of the kidneys and secrete epinephrine and norepinephrine, the “fight or flight” hormones.

The hormones used in the endocrine system are grouped into three classes:  steroids, peptides, and amines.  Steroid hormones pass through the plasma membrane to bind to the nuclear membrane receptors.  This produces an activated hormone-receptor complex that binds to DNA and activates specific genes to increase the production of proteins (Faradee, 2001).   The steroids are not stored in cells and are controlled by rate of synthesis.  Non-steroid hormones, on the other hand, are water-soluble and bind to the plasma membrane receptors instead of entering the cell.  Non-steroid hormones generate a chemical signal inside the target cell to trigger second messengers to activate other intracellular chemicals in order to produce an appropriate response (Farabee, 2001).

Peptides and Amines are short chains of amino acids secreted by the pituitary, parathyroid, heart, stomach, liver, and kidneys.  The thyroid and adrenal medulla secrete amines derived from the amino acid tyrosine (Farabee, 2001).  Peptides and amines are stored in secretory granules and cytoplasm to be used when needed.  The hormones secreted by the endocrine system cross over into other systems in the human body.  If any of the glands in the endocrine system are not secreting the proper amounts of a particular hormone, then it could affect one or more of the other systems.  If any of these hormones are lacking or too plentiful, the body is thrown out of homeostasis.

Farabee, M.J. (2001)  The Endocrine System.  Retrieved on March 11, 2012, from www.emc.maricopa.edu/faculty/farabee/biobk/biobookendocr.html