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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.

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Vital signs (blood pressure, temperature, pulse rate, respiration rate) should be taken before any drug administration. Patients should be informed not to use tobacco or caffeine at least 30 minutes before their appointment.

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Of the estimated 2 million heroin users in the United States, 600,000–800,000 are considered hardcore addicts. Heroin addiction is considered to be one of the hardest addictions to recover from.

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In ancient Rome, many of the richer people in the population had lead-induced gout. The reason for this is unclear. Lead poisoning has also been linked to madness.

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Multiple experimental evidences have confirmed that at the molecular level, cancer is caused by lesions in cellular DNA.

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Negative feedback control of a regulated variable. Negative feedback control of a regulated variable.
Video: Phases of the ovarian cycle

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