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There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
If all the neurons in the human body were lined up, they would stretch more than 600 miles.
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.
Hyperthyroidism leads to an increased rate of metabolism and affects about 1% of women but only 0.1% of men. For most people, this increased metabolic rate causes the thyroid gland to become enlarged (known as a goiter).
After 5 years of being diagnosed with rheumatoid arthritis, one every three patients will no longer be able to work.