Bone Remodeling Essay Example | Topics and Well Written Essays - 1750 words

Bone Remodeling - Essay Example Bone remodeling is a process of a lifetime in which the old bone is removed by the osteoclasts and replaced by osteoblasts.(9) Parafitt AM., 2002 described the cellular basis of the normal bone remodeling sequence in the human adult to a cycle that constitutes three stages, quiescence, activation, resorption, reversal, formation, and return to quiescence (1). The major reasons of remodeling is to enable the bones to respond and adapt to mechanical stress as occurs as a result of physical exercise and during the mechanical lading as occurs during orthodontic tooth movement. This article outlines the major research carried out in the past decade in the cellular basis of bone remodeling. The aspects included are the relationship between the hormone and localized factors that affect the phenomenon. The dependence of the localized factors and the proteins during the bone resorption is critically discussed. The understanding provided by the RANK/RANKL/OPG paradigm for both the differentiat ion and their activation of the osteoclast is also discussed. Bone undergoes constant bone remodeling and it is a very complex process. In his review article Hill PA., 1998 described four stages involved in bone remodeling, namely, resorptive phase reversal phase, formative phase and resting phase. In the resorptive phase, the activated multinucleated osteoclast derived from bone marrow resorbs a discrete area of mineralized bone matrix. The latter stage than follows in which the osteoblast precursor cells, which can locally proliferate and differentiate into osteoblast migrate into the resorption lacuna and disclose the former osteoclastic activity. The osteoblast deposits new bone matrix which is initially unmineralized and called osteroid and in this way fills the resorption lacuna. This phase is the formative phase. Finally the resting phase is followed. Once embedded in the osteroid, the osteoblast matures into terminally differentiated osteocytes. The osteoblast lying on the surface on the surface of the newly formed bone packet are quie scent lining cells activated.(11) Osteoclast and osteoblast lay the basis of bone remodeling and significant research is been carried out in the past decade. It is known that both osteoblasts and osteoclasts function under the regulation of many factors(3, 7), systemic and local among which insulin, insulin-like growth factors-I, bone-morphogenetic factors and Wnt protins are the potent bone anabolic factors(13). Recently, it was reported that phosphoinosidine-dependent serine-threonine protein kinase Akt plays a major role in signaling of the potent bone anabolic factors. Akt1, a major Akt in osteoclast and osteoblast has a novel role. Akt1 phosphorylates the transcription factor FoxO3a to restrict its nuclear localization, thus suspending the transactivation of its target gene Bim which is also known to be a potent proapoptotic molecule in osteoblasts. This research established that Akt1 plays a crucial regulator of osteoclast and osteoblast by promoting the differentiation and su rvival to maintain bone marrow and turnover.(8) Bone resporption is mainly dependent on a cytokine RANKL (receptor activator of nuclear factor kappa B ligand), which is a TNF (tumor necrosis factor), that is vital for the osteoclast formation, activity and survival

How has sept. 11th effected the economy in the united states Essay

How has sept. 11th effected the economy in the united states - Essay Example It is hardly possible to meet the person who is unaware about the events of September 11. Thousands of people became victims of the biggest terrorist attack in the history of United States. The single day has changed the life of Americans, their perception of security and human dignity. The attack was well planned and confidently carried out, it was impossible to foresee this tragedy. Or was it? Four years have passed since that time but the world is still talking about it. One of the major outcomes of September 11 has become the closer examination of visitors to United States. The concept of racial profiling has become an inevitable part of national security. Nevertheless, is it reasonable to label the whole Arabian world as potentially dangerous because of the action of several individuals? When the American nation has managed to overcome the terror, the cardinal actions had to take place. Among the first initiatives was to use racial profiling in screening out the potentially dangerous immigrants and visitors to the country. Of course, the Arabs have become number one suspects and were closely examined. Was this targeted screening justified or was only the way to hide discriminatory attitude towards Arabian nation? Most likely, American government was not ready for attack of such level and racial profiling was the only effective way to prevent further attack. However, some of the actions are hard to explain and understand. For example, prior to September 11 Americans have rejected racial profiling, but since that day the public opinion has reversed. More than 1000 Arabs and Arab Americans (those who were born and lived all their lives in United States) were detained even though not a single of them has been charged with any formal offense (Davis, N., 2001). Students were kindly invited to visit their Arabian families in native countries with the hope that they will never return to United