Steroids are a class of lipid hormones synthesized from cholesterol. They regulate metabolism, immune response, reproduction and other essential biological processes, the 1999 textbook "Biochemistry" notes. Subdivided into five classes according to their primary site of production, steroids have wide-ranging effects on a variety of tissues.
Mineralocorticoids and glucocorticoids are both synthesized in the adrenal cortex. They maintain normal bodily function by supporting cellular processes and protecting against environmental stresses.
Mineralocorticoids such as aldosterone increase fluid retention in order to maintain blood volume. They act on kidneys, sweat glands, colon and salivary glands to prevent sodium loss and electrolyte imbalance, which can cause life threatening conditions such as cardiac arrhythmias and circulatory collapse, according to Leonard R. Johnson's 2003 textbook "Essential Medical Physiology."
Glucocorticoids are also synthesized in the adrenal cortex and promote kidney function. However, they are most well-known for their anti-inflammatory effects. Cortisol is commonly used to treat a variety of allergic and autoimmune conditions including poison ivy, asthma, rheumatoid arthritis and transplant rejection, they act by depressing immune function on the molecular, cellular and tissue levels. In addition, they help to constrict blood vessels at the site of inflammation, reducing swelling and pain in the area. In general, these effects help to limit injury damage, Johnson's book notes.
Glucocorticoids are named for their ability to regulate metabolism. They prevent low blood sugar by increasing insulin resistance in muscle and adipose tissue, which reduces glucose uptake. In addition, they stimulate glucose synthesis in the liver. This process requires a supply of amino acids, which are generated from the breakdown of muscle and lymphoid tissue.
The MayoClinic.com warns that prolonged use of corticosteroids can be dangerous due to the widespread effects on immune function, metabolism, muscle degeneration and other processes. Side effects include susceptibility to infection, diabetes, tendon and muscle injury and many other complications.
Glucocorticoids also support lung development during the last stages of pregnancy, when the fetus must prepare to breathe oxygen for the first time.
The testes are the major site of androgen production, which control male reproductive development.
During puberty, testosterone stimulates growth and development of the testes themselves, as well as that of vertebrae and long bones, which fuels the growth spurt, the larynx and vocal chords, which lowers the voice, glands in the skin, which causes acne, and hair on the face, chest and pubic region. Interestingly, it causes decreased hair growth on the scalp, resulting in a receding hairline and baldness later in life, according to Johnson's text.
Testosterone's impact on physique is the major incentive for illegal steroid use in athletics, with muscular arms and shoulders, increased red blood cells, physical resilience and positive mental state being desirable characteristics. However, the testes also convert testosterone to estradiol, an estrogen that can cause side effects such as breast growth when too much is present.
Testosterone also controls sex drive in both men and women.
Estrogens are produced by the ovaries and prepare a woman to conceive, carry and raise a child.
During puberty, estrogen stimulates growth hormone secretion, female reproductive organ and breast development, fat deposition on hips and thighs, changes in bone structure such as widening hips and increases in bone density.
When a woman reaches maturity, estrogen promotes growth of the lining of the uterus to prepare for embryo implantation and causes physiological changes that promote sperm motility. It increases blood flow to supply the fetus with nutrients, induces uterine contractions during birth and stimulates prolactin secretion, according to Johnson's text.
Estrogen also supports heart health by acting directly on the heart muscle and by altering fats found in the blood, according to work published in the 1990s in the medical journals "The Lancet" and "Endocrinology Metabolism Clinical North America."
Progestagens such as progesterone are sythesized in the corpus luteum. While progesterone also prepares the body for successful pregnancy by stimulating uterine development and breast growth, it is most essential in maintaining the pregnancy. Progesterone suppresses the mother's immune system to prevent rejection of the foreign child. It also inhibits uterine contraction until the fetus is ready for birth. During pregnancy high levels of progesterone prevent lactation. The precipitous drop in progesterone after delivery releases lactation, and also can result in postpartum depression due to the hormone's affects on the brain, according to "Essential Medical Physiology."
- "Biochemistry"; Lubert Streyer; 1999
- "Essential Medical Physiology"; Leonard R Johnson; 2003
- "Endocrinology Metabolism Clinical North America"; The effects of hormone replacement therapy on coronary heart disease; M.M. Sotelo, S.R. Johnson; 1997
- "The Lancet"; Beneficial effect of estrogen on exercise- induced myocardial ischaemia in women with coronary artery disease; Rosano GM, Sarrel PM, Poole-Wilson PA et al; 1993.
- "Clinical Journal of Sports Medicine"; Complications associated with the use of corticosteroids in the treatment of athletic injuries. Nichols AW; Sept. 2005.