A suitable terpene chain can be condensed into a four-ring framework
that is typical of another class of lipids: steroids. Cholesterol
(right) is a steroid molecule that is an important part of many
membranes, but which can cause trouble when it occurs as a fatty
deposit in blood vessels and chokes off blood flow. Cortisone, testosterone,
and other steroids are hormones - chemical messengers that are released
in minute amounts at one location in the body, and have profound
regulatory effects at a number of other distant locations.
Cortisone's main function is to adjust the level of glucose in
the blood by conversion of liver glycogen (see Page
23) to glucose. Testosterone is a male sex hormone; and other
steroid hormones control the levels of Na+, Cl-,
and water in the body, influence sexual development, and control
inflammation and allergic response.
Steroid and polypeptide (protein) hormones seem to be the regulatory
messengers in all plants and animals above the one-celled level,
carrying information about the state of one group of cells to another
group of cells that are capable of taking appropriate action.