I could see the inevitable when I got halfway down the hill: going too fast to make the bend at the bottom, couldn't get enough grip on the tyres to slow down. Apparently I was roaring with laughter as the bike and I cartwheeled round the bend.What fun.
So my left kneecap had lost most of the top layer of skin. Ten days later and there's a healthy size scab there. Vivid red at the edges and shrinking fast. Also irresistibly itchy, and I'm appalled to find that even at my advanced age(nearly 60) I still want to pick at it!
Wiki has a good article on skin repair, which says Old Age can inhibit or completely stop skin regeneration. That's a bit worrying - does anyone on OM know when Old Age might kick in here? We all pick up a few scrapes when we're out having fun. It would be daunting to find out those scrapes are not going to repair.