The sciatic nerve starts in your lower back, runs down the back of your thigh and branches all the way to your foot. At its origin, it's about 2 cm wide: the longest and thickest nerve in your body. It bundles thousands of fibers that drive the leg's muscles and carry its sensations.
Every day, your kidneys filter around 180 liters of blood plasma, about a bathtub's worth. Yet you only have about 3 liters of plasma, so it passes through your kidneys some sixty times a day. Over 99% of the filtered water is reabsorbed, leaving just one to two liters of urine.
A 70 kg adult is made of about 7 × 10²⁷ atoms, or seven billion billion billion. The observable universe is thought to hold on the order of 10²² to 10²⁴ stars. Even with the high estimate, you contain thousands of times more atoms than there are stars in the entire visible cosmos.