Steroid hormones are molecules produced and then secreted by the glands of the endocrine system. These lipid-soluble hormones cause physiological changes within a target cell by passing through the cell’s primary lipid membrane. Steroid hormones are unique in that they are produced from the body’s stores of cholesterol, which imbue them with their lipid-soluble status. Molecules with this status tend to be more physiologically active within the cell because the phospholipid nature of the membrane keeps out molecules that are not lipid-soluble. As steroid hormones are released into the body’s bloodstream, they seek out cells that have associated receptors and attach to them to initiate a specific response within the target cell.
Once a steroid hormone attaches to its associated receptor site on the cell membrane, it travels into the nucleus of the cell, where it binds to another specialized receptor on its nucleic chromatin. Next, the steroid hormone initiates a cellular process called transcription. During transcription, the hormone essentially orders the cell to produce another molecule, messenger ribonucleic acid (mRNA). After the mRNA molecules are transported, they go through one last process, translation, after which they are able to produce the basic building blocks of the human body, proteins.
Each steroid hormone contributes in a different way to ensure the smooth functioning of a variety of different physiologic functions within the body. Some common steroid hormones are testosterone, progesterone, and cortisol. Progesterone is the catalyst for many of the changes that happen in a woman’s body during pregnancy. It helps to thicken the endometrium inside the uterus, ensuring that that a fertilized egg will be able to implant and that the mother will be able to nourish a fetus adequately during pregnancy. Progesterone is also implicated during breast feeding, as it initiates milk production in the mammary glands.
Testosterone is responsible for many actions related to the reproductive system, as well. It is the hormone that is chiefly implicated in determining what sex a fetus will become in the womb. After birth, testosterone directs the development of sexual characteristics during adolescence. Bodybuilders, who often use anabolic steroids, rely on the synthetic steroid’s molecular similarity to testosterone to build muscle mass. Steroid hormones are also used in medical applications to treat hormonal disorders and deficiencies. The hormones have been proven to be relatively safe in these medical applications, but overuse has been linked to baldness, certain types of cancer, and liver disease.