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Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.
In most cases, kidneys can recover from almost complete loss of function, such as in acute kidney (renal) failure.
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.
When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
In 1886, William Bates reported on the discovery of a substance produced by the adrenal gland that turned out to be epinephrine (adrenaline). In 1904, this drug was first artificially synthesized by Friedrich Stolz.