Your daily rhythm is run by about 20,000 neurons sitting just above where the optic nerves cross. Left without cues, this clock runs on a cycle slightly longer than 24 hours, about 24 hours and 10 minutes. Every morning, light entering your eyes resets it, like a watch that runs a little slow.
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.