AboutJohn Locke Expertise I will answer all biology-related questions through the undergraduate level. I will explain unclear concepts and suggest approaches to solving problems, but would prefer not to completely solve homework problems for you. If you are completely stumped on homework, tell me what you already know and I will help you as much as possible. Please do not ask me for ideas on school research projects; part of research is determining a suitable area of investigation, and that's not a task that should be completed by someone else.
Experience I have a BS in Bioengineering with a concentration in Chemical Engineering (which included a heavy focus on biology), and have taught biology, biochemistry, and related subjects for some time now.
Education/Credentials BS Bioengineering, Penn State University
MCAT/DAT/OAT Instructor
Question 1. What is the bump a person gets on their head or hand when their bone hits something hard?
2. Is there a way bone hardness can be increased. I have seen these "Xtreme Matrial Arts" people break bricks like crackers. Of course, I am not upto trying anything of that sort, but how exactly does their bone hardness increase well above ordinary. I would think by regular hitting the bone might become hard, but it also leads me to think it could get damaged. So how does it become hard?
Is there a site that explains this with details of the bone structure?
Answer Thanks for using AllExperts. I think that the bumps you are referring to may be from hematomas, which are masses of red blood cells that have escaped blood vessels due to injury and then collect within the surrounding tissue. Injuries like that are accompanied by acute inflammation, which causes the swelling due to an accumulation of fluid in the area. Those kinds of bumps are temporary and will resolve when the acute inflammation goes away, usually within two weeks.
Someone who repeatedly strikes a single part of their body against a surface may experience increased bone growth at that site of injury, making a permanent bump that is actually from new bone growth. This bump is known as an exostosis. This process is a protective measure that seeks to make the bone less likely to break if further strikes occur. This also gets at your second question about bone remodelling.
Bone is living tissue with its own blood supply, cells, nerves, and ability to adapt to changing circumstances. Bone is not static, but constantly changes according to the demands that are placed on it--a process known as remodelling. Certain bone cells (osteoblasts) deposit mineralized calcium that makes up the hard portion of bone, and other cells (osteoclasts) dissolve away that calcium. The balance between these two processes is what determines bone growth. When bone is repeatedly stressed--as the tibia, fibula, and femur are from long-distance running--more bone will be deposited than taken away, and bone hardness will increase. When very little stress is placed on bone (as happens with astronauts who experience long-term weightlessness), more bone is taken away than deposited and bone hardness decreases. How exactly this is controlled is still unknown, but it is thought to relate to the generation of small electrical current within bone when stress is placed on it. This entire process is known as Wolff's Law. See here: http://alliraph.wordpress.com/2007/10/22/the-wolffs-law/
To reference your example, martial artists often experience increased bone density in the areas of the body that they use to strike--hands, shins, feet, etc. You also asked about the difference between between increasing the hardness of bone and damaging it. The difference lies in how much stress is applied and how quickly. Large amounts of stress applied very quickly to a bone will damage it, but lower amounts applied more often will cause it to increase in density. That is the key difference.
Bone hardness is assessed by the bone mineral density (BMD) test. More information about it can be found at the website below:
