Fibroblasts? Really, fibroblasts as the key to engineering Spider-Man's web-squirting palms? Yes, fibroblasts. They even sound cool.
What are fibroblasts? They're cells that build connective tissue. They hang out in fascia, tendons, joint capsules, and other connective tissues and produce tough bundles of fibers made out of collagen. In a way, you could say that fibroblasts can spin a web, any size(1)!
When you tear a muscle or get tendinitis, or bruise or cut yourself, an inflammatory reaction results which helps to promote a series of events that will help repair dead or damaged tissues(2). Fibroblasts and some special types of muscle cells will move into the area to repair the damaged tissue. This repair process usually results in a scar.
Sometimes if a tendon, or the superficial connective tissue below the skin, becomes chronically stressed, abraded, and inflamed, fibroblasts will migrate to the area and begin to form a sack of connective tissue called a bursa, to try and cushion the area being stressed.
What does a knee have to do with bursae? They're everywhere, that's what. If you want to experience a bursa first hand, pinch up the skin over your knee cap and roll it between your fingers. Feel how slippery it is inside? That's because there's a (pre-patellar) bursa there and you are rolling its slimy surfaces across one another.
Bursae(3) are normal parts of the musculoskeletal system. They are connective tissue sacks full of slimy synovial fluid(4). They are usually located between a tendon and a bone and provide cushioning to protect the tendon and its muscle from injury. The German word for bursa is schleimbeutel, which means "slime bag," which is exactly what they are. I love German!
As I said, you can grow extra bursae if you're chronically irritating an area. So... what kind of activity could a teenage male be engaged in on a regular basis that would create so much friction and abrasion of the palms, that his body would need to alter his palmar structure to protect it? Hmmmmm... it would have to be some kind of grasping, or rubbing, repetitive activity, performed regularly over weeks or months. I'm sure I can't think of anything.
Next time I'll tie these parts together to describe Parker's incredible transformation...
1. Is anyone keeping track of how many times I have recycled this joke?
2. For you trivia buffs, this inflammatory reaction is pretty much the same type of thing that I mentioned in the posts about Face/Off. The context is slightly different, but once again, we see that the body has only a limited number of ways to respond to trouble, and inflammation is a common response. Inflammation is also the reaction that would cause those hives Peter was experiencing in my last post.
3. Bursa is singular, bursae (pronounced bursay, or bursee, depending on who's arguing the loudest) is plural.
4. Synovial fluid is a slimy substance with the consistency of egg whites. It's just like that, really. I dissected a cadaver once and there was still synovial fluid in his knee. It's very clingy. Ick! Synovial fluid is secreted by a membrane called the (you guessed it!) synovial membrane, which lines the bursa, and also lines the inside of your joint capsules. The stuff helps lubricate surfaces to reduce wear and tear as they slide across one another.