Your lungs hold around 480 million alveoli, tiny air sacs wrapped in capillaries. Laid flat, their walls would offer a gas-exchange surface on the order of 70 square meters, the floor area of a family apartment. In places, the barrier between air and blood is less than a thousandth of a millimeter thick.
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.