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In most cases, kidneys can recover from almost complete loss of function, such as in acute kidney (renal) failure.
Your skin wrinkles if you stay in the bathtub a long time because the outermost layer of skin (which consists of dead keratin) swells when it absorbs water. It is tightly attached to the skin below it, so it compensates for the increased area by wrinkling. This happens to the hands and feet because they have the thickest layer of dead keratin cells.
Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
Addicts to opiates often avoid treatment because they are afraid of withdrawal. Though unpleasant, with proper management, withdrawal is rarely fatal and passes relatively quickly.
Multiple sclerosis is a condition wherein the body's nervous system is weakened by an autoimmune reaction that attacks the myelin sheaths of neurons.
![A comparison between chromosomes found in a normal human cell and a cancer cell from the same person](https://biology-forums.com/gallery/47/medium_33_25_06_11_10_34_04.jpeg)
![The visual field as seen by a person with (a) glaucoma, (b) macular degeneration, and (c) cataracts.](https://biology-forums.com/gallery/47/medium_33_29_07_11_7_45_50.jpeg)