Most steroids in human bodies are hormones, messengers, that carry signals from one organ or tissue to another. Cholesterol, however, the most well known of steroids (even though most people don't realize it is a steroid), has a structural role. It helps in the construction of cell walls; most adults have about a half a pound of it distributed in their bodies.

Here are pictures of some of the common steroids discussed in class:

Name	Line Structure	Model
Estradiol
Testosterone
Cortisone
Progesterone
Cholic Acid
Cholesterol

Estradiol and testosterone are the female and male "sex hormones", respectively. This simply means that they are responsible for telling tissues and organs that they belong to a female or male person, thus guiding their proper development. Their similarity of structure is striking! How curious to think that a methyl group and a few hydrogen atoms make such an enormous difference.

Cortisone is an example of a corticosteroid, so named for its formation in the cortex of the adrenal glands. Corticosteroids, among other things, regulate the excretion of sodium ions by the kidneys, thus controlling our blood pressure.

Progesterone is the "pregnancy" hormone. Its release upon fertilization of an egg signals the pituitary gland to suppress ovulation and the uterus to prepare for implantation of an embryo. Simulating its action is the basis of oral contraceptives.

Cholic acid is a bile acid, as well as the parent structure of all steroids. It regulates the digestion and metabolism of fats. Cholesterol, as mentioned, is a structural steroid. We all are familiar with the problem of its deposition in arteries blocking proper flow of blood to the heart and brain.