In adulthood, our bones stop growing and modeling, but continue to go through a process of bone remodeling. In the process of remodeling, bone tissue is degraded and built up at the same location. About 10 percent of bone tissue is remodeled each year in adults. As observed in Video 9. This is why exercising, especially when it involves weight-bearing activities, increases bone strength.
Video 9. The first step in bone remodeling is osteocyte activation see Figure 9. Osteocytes detect changes in mechanical forces, calcium homeostasis, or hormone levels. In the second step, osteoclasts are recruited to the site of the degradation. Osteoclasts are large cells with a highly irregular ruffled membrane. These cells fuse tightly to the bone and secrete hydrogen ions, which acidify the local environment and dissolve the minerals in the bone tissue matrix. This process is called bone resorption and resembles pit excavation.
Our bodies excavate pits in our bone tissue because bones act as storehouses for calcium and other minerals. Bones supply these minerals to other body tissues as the demand arises. Bone tissue also remodels when it breaks so that it can repair itself.
Moreover, if you decide to train to run a marathon your bones will restructure themselves by remodeling to better able sustain the forces of their new function. After a certain amount of bone is excavated, the osteoclasts begin to die and bone resorption stops. In the third step of bone remodeling, the site is prepared for building. These first three steps take approximately two to three weeks to complete.
In the last step of bone remodeling, osteoblasts lay down new osteoid tissue that fills up the cavities that were excavated during the resorption process. Osteoid is bone matrix tissue that is composed of proteins such as collagen and is not mineralized yet. To make collagen, vitamin C is required. A symptom of vitamin C deficiency known as scurvy is bone pain, which is caused by diminished bone remodeling.
After the osteoid tissue is built up, the bone tissue begins to mineralize. The last step of bone remodeling continues for months, and for a much longer time afterward the mineralized bone is continuously packed in a more dense fashion. Thus, we can say that bone is a living tissue that continually adapts itself to mechanical stress through the process of remodeling. For bone tissue to remodel certain nutrients such as calcium, phosphorus, magnesium, fluoride, vitamin D, and vitamin K are required.
The skeletal system aids in movement, provides support for and protects organs, synthesizes platelets and red and white blood cells, and serves as a storage depot for minerals, such as calcium. The skeleton is composed of connective tissues including bones, cartilage, tendons, and ligaments.
Bones are made up of a periosteum that surrounds compact bone, which in turn surrounds trabecular bone. Bone marrow resides within the trabecular bone. Bone tissue cells are osteoprogenitor cells, osteoblasts, osteoclasts, and osteocytes. Bone is a living tissue that adapts to mechanical stress via the remodeling process. Bone remodeling is a multifaceted process involving four steps: osteocyte activation, osteoclast-mediated bone resorption, surface preparation, and osteoblast-mediated bone building.
Bone is stronger than some steel. At birth we have over bones. As we grow up, some of the bones begin to fuse together as a result an adult has only bones. The muscles of the eye move more than , times a day. If you remove the minerals from a bone by soaking it overnight in a six percent solution of hydrochloric acid, it will become so soft, you could tie it in a knot.
There are 22 bones in the human skull. The hardest bone in the human body is the jawbone. The human skeleton renews once in every three months. The human body consists of over muscles. Human bone is as strong as steel but 50 times lighter. Human fingers stretch and bend about 25 million times in a normal lifetime. Human speech is produced by the interaction of 72 muscles. Humans have more facial muscles than any other animal on earth — 22 on each side of the face.
It takes 17 muscles to smile and 43 to frown. When it comes to kicks, "they can obviously generate more force, since there's more body mass behind it," Bir said. After looking at kicks from several different fighting styles, they found that experts could generate up to 9, newtons with them, equal to roughly a ton of force.
A quick, sharp blow that delivers some 3, newtons of force has a 25 percent chance of cracking an average person's rib, she said. It takes more force to fracture the femur, Bir noted — maybe some 4, newtons — since that long thighbone is meant to support the body.
The amount of damage a blow inflicts also varies due to factors such as the amount of muscle or fat covering a bone and the angle at which the blow lands, as well as the age and health of a person, which can affect bone strength. Although it makes sense that a massive fighter can unleash more powerful blows than a lightweight, "it's also about how much of the mass of your body you can recruit," Bir said.
When it comes to knocking someone out with a punch, "it's less about the force of the blow than it is getting the head to whip around, to move in a rotational kind of way," Bir said.
0コメント