Hormones are chemicals that naturally occur in the body. These chemicals direct many biochemical events, including energy storage and utilization, maintenance, and growth. Hormones are released mainly by the endocrine glands. Specific endocrine glands include the pituitary, thyroid, adrenals, parathyroids, gonads (e.g., testes and ovaries), and the islets of Langerhans which are located in the pancreas. The endocrine glands release very small quantities of hormones into the blood, but these small quantities have a large impact throughout the body.

From a chemical standpoint, hormones can be divided into three categories. The first category is made up of hormones that are derived from tyrosine, a type of amino acid. Specific hormones that belong to this category are epinephrine and norepinephrine. The second category of hormones are those that are derived from steroids, a class of chemicals based on cholesterol. Steroidal hormones include testosterone, estradiol, progesterone, cortisol, and aldosterone...