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Autoimmune diseases occur when the immune system destroys its own healthy tissues. When this occurs, white blood cells cannot distinguish between pathogens and normal cells.
The ratio of hydrogen atoms to oxygen in water (H2O) is 2:1.
There are major differences in the metabolism of morphine and the illegal drug heroin. Morphine mostly produces its CNS effects through m-receptors, and at k- and d-receptors. Heroin has a slight affinity for opiate receptors. Most of its actions are due to metabolism to active metabolites (6-acetylmorphine, morphine, and morphine-6-glucuronide).
Astigmatism is the most common vision problem. It may accompany nearsightedness or farsightedness. It is usually caused by an irregularly shaped cornea, but sometimes it is the result of an irregularly shaped lens. Either type can be corrected by eyeglasses, contact lenses, or refractive surgery.
Calcitonin is a naturally occurring hormone. In women who are at least 5 years beyond menopause, it slows bone loss and increases spinal bone density.