We pass our existence within this warm wobble of flesh and yet take it almost entirely for granted. how many among us know even roughly where the spleen is or what it does? Of the difference between tendons and ligaments? Or what our lymph nodes are up to? How may times a day do you suppose you blink? Five hundred? A thousand? You've no idea, of course. Well, you blink fourteen thousand times a day—so much that your eyes are shut for twenty-three minutes of every waking day. Yet you never have to think about it, because every second of every day your body undertakes a literally unquantifiable number of tasks—a quadrillion, a nonillion, a quindecillion, a vigiantillion (these are actual measures), at all events some number vastly beyond imagining—without requiring an instant of your attention.
-Bill Bryson, The Body: A Guide For Occupants
Ed Note: To save you the trouble, a vigintillion is, in US measurements, a number equal to 1 followed by 63 zeros: 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000.
You can look up the spleen yourself.