Steroids are a type of hormone largely secreted by the adrenal glands and testicles or ovaries. They are derived from cholesterol, which is a fat soluble molecule. Enzymes in the cells of the adrenal glands, testicles or ovaries rearrange the structure of cholesterol to make corticosteroids, androgens or estrogens.
Corticosteroids
According to the text "Physiology" by Linda S. Costanzo, two classes of corticosteroids exist: glucocorticoids and mineralocorticoids. These are called corticosteroids because they are synthesized in the cortex, or outer layer, of the adrenal gland. Glucocorticoids are stress hormones. They have a number of functions in the body, including decreasing inflammation, increasing glucose which a sugar which is a major source of energy for cells and increasing cognitive abilities such as alertness. Cortisol is an example of a glucocorticoid.
Mineralocorticoids such as aldosterone are also released by the adrenal glands outer layer. These steroids signal the kidneys to retain sodium and fluids and raise the blood pressure.
Male Sex Steroids
Male sex steroids are called androgens, the most prevalent of which is testosterone. They are synthesized primarilly in the testes of males and the adrenal glands in females. Androgens are responsible for libido and male secondary sexual characteristics such as the growth of male pattern hair and hair loss, deepening of the voice, increased sweat gland activity, increased bone and muscle mass and production of more red blood cells.
Female Sex Steroids
Female sex steroids or estrogens such as estradiol are released from the ovaries. In males, some testosterone is converted into estrogen in fatty tissues by the enzyme aromatase. They contribute to the formation of female secondary sexual characteristics such as breast development. In addition, they help control the menstrual cycle by increasing the thickness of the wall of the uterus.
References
- "Physiology—Fourth Edition"; Linda S. Costanzo; 2009
- Encyclopaedia Britannica: Androgen
