Science, Tech, Math › Science Steroids - Molecular Structures Share Flipboard Email Print MOLEKUUL/SCIENCE PHOTO LIBRARY / Getty Images Science Chemistry Molecules Basics Chemical Laws Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated December 07, 2019 There are hundreds of different steroids found in living organisms. Examples of steroids found in humans include estrogen, progesterone, and testosterone. Another common steroid is cholesterol. Steroids are characterized by having a carbon skeleton with four fused rings. The functional groups attached to the rings distinguish the different molecules. Here's a look at some molecular structures of this important class of chemical compounds. The two main functions of steroids are as components of cell membranes and as signaling molecules. Steroids are found throughout the animal, plant, and fungi kingdoms. Aldosterone Aldosterone is a steroid hormone. In humans, its function is to cause the kidney tubules to retain sodium and water. Ben Mills Cholesterol Cholesterol is a lipid that is found in the cell membranes of all animal cells. It also is a sterol, which is a steroid characterized by an alcohol group. Sbrools, wikipedia.org Cortisol Cortisol is a corticosteroid hormone produced by the adrenal gland. It sometimes is referred to as the "stress hormone" as it is produced in response to stress. Calvero, wikipedia commons Estradiol Estradiol is one form of the class of steroid hormones known as estrogens. Anne Helmenstine Estriol Estradiol is one form of the class of steroid hormones known as estrogens. Zerbor / Getty Images Estrone Estrone is one form of estrogen. This steroid hormone is characterized by having a ketone (=O) group attached to the D ring. Anne Helmenstine Progesterone Progesterone is a steroid hormone. Benjah-bmm27, wikipedia.org Progesterone Progesterone belongs to a class of steroid hormones called progestogens. In humans, it is involved in the female menstrual cycle, embryogenesis, and pregnancy. Anne Helmenstine Progesterone is a female sex hormone involved in pregnancy, embryogenesis, and the menstrual cycle. Testosterone Testosterone is one of the steroid hormones. Anne Helmenstine Testosterone is an anabolic steroid. It is the principal male sex hormone.