Hormones are types of chemicals that are released into the body by glands. They carry messages to the cells to instruct them what to do. There are two types of hormones, ones that are dissolved in fats (known as lipids), and ones that are dissolved in water.
Fat-Soluble Hormone Characteristics
Fat soluble hormones are derived from cholesterol. The main class of these hormones are Steroids.
As they do not dissolve in water, they need a protein "carrier" to deliver their message. They are able to pass through the membrane of a cell directly, after which they bind to a protein molecule which allows them to carry the signal to the nucleus. These types of hormones tend to have a long half life.
Examples: testosterone, cortisol, fludrocortisone estrogen, progesterone, dihydrotestosterone.
Water-Soluble Hormone
Water-soluble hormones are derived from Amino Acids and are mostly Peptides. Unlike fat-soluble hormones, they cannot pass through the membrane into the cell, so they bind with protein receptors on the outside of the membrane and rely on a "second messenger" system. This changes the shape of the protein which activates with another protein inside the cell to transfer the message. They are excreted quickly through the kidneys, so have a short half-life.
Examples: Thyroid
Releasing Hormone
(TRH), Vasopressin, Growth Hormone (Somatropin), Prolactin.
