Osteoclasts main function is the breakdown of bone in the extracellular matrix. This is known as resorption. They play the main role in bone modelling and remodelling. (Ozawa and Amizuza, 1994).
Osteoblasts have a deeply ruffled membrane which released lysosomal enzymes and acid which digest protein and mineral components of the bone matrix. It is probable that they are controlled by surrounding osteoblast phenotype. (Thibodeau, 2007).
Bone remodelling all contributes to bone density. Osteoblasts build or replace our bone when we are young. Bone density is determined on the rate of which osteoclasts break down bone and where osteoblasts build bone tissue. (Bontrager and Lampiano 2010).
In conclusion, it can clearly observed that each of these bone forming cells are unique in structure and function. Each all help form the bone in different processes. The functional of bone cells is vital to our bones as the human body would not be able to function without them.
Describe the process of mitosis and outline how cell aging and cell death affects normal cell replication.
The processes of mitosis are the main characteristic of cell replication. Mitosis is an important feature that takes place in most of the cells of our bodies. It is an important process as it regenerates tissue in the body. The process must be very precise so that each cell receives a complete copy of genetic information. (Shier, Butler & Lewis, 2007).
Just as equally important are the processes of cell aging and cell death. These can effect cell replication leading to dysfunctional cells which can lead to mutations and other effects on the body.
The process of Mitosis can be defined as “the orderly division of the nucleus of a cell that ensures that each new nucleus has the same number and kind of chromosomes as the original nucleus”. (Stein, 1996). Mitosis is specifically the process of division of the chromosomes (Tortora & Derrickson, 2009). Chromosomes replicate and form two sets of chromosomes in the form of two separate and equal nuclei. (Stein, 1996).
Mitosis is a process of cell division which involves only somatic cells. Somatic cells are all cells in the body other than germ cells. (Tortora & Derrickson, 2009).
It occurs to increase cell numbers accruing extensively in the skin, epithelium and gastrointestinal tract where cells are routinely lost. (Henderson and Macdonald, 2004).
In relation to mitosis, there is the mitotic phase of the cell cycle which consists of nuclear division. Mitosis distributes two sets of chromosomes into two separate nuclei. Although mitosis is a continuous process, the entire process is divided into five stages: interphase, prophase, metaphase, anaphases and telephase. (Tortora & Derrickson, 2009).
Interphase is the “resting stage”. It is preparing itself for the processes of mitosis with cell growth, replication of chromosomes and other activities. The genetic material is referred to as chromatin. (Loren1999).
Prophase is the first stage of mitosis. The cells begin to coil, shorten and become distinct. (Loren, 1999). During this phase the nuclear membrane breaks up and disappears. The nucleolus vanishes. The chromosomes shorten and thicken. The spindle fibres extend outward from the centrosomes which move to the opposite sides of the cell. (O’neill, 2010).
During metaphase the chromosomes line up on the equator of the cell know as the metaphase plate. The nuclear envelope has totally disintegrated. (Tortora & Derrickson, 2009). The polar fibres reach the centromeres of the chromosomes and have begun interacting with them. (Stein, 1996).
Metaphase prepares the cell for separation of chromatids. (Loren, 1999).
The sister chromatids separate at the centromeres, and can be now called chromosomes. Mitotic spindle fibres dissolve and disappear. (Loren, 1999).
This stage is known as anaphase. The mitotic spindle pulls the chromosomes to the poles. (Tortora & Derrickson, 2009).
Telophase divides the cell into two. (Stein, 1996). The sets of chromosomes uncoil and form back into threadlike chromatin. The mitotic spindle breaks up and a nuclear envelope is formed around the chromatin mass and nucleoli reappear in the identical nuclei. In late anaphase a process called cytokinesis begins and is completed after telophase. It forces the two sets of chromosomes to separate into two cells where interphase then occurs and the whole process is repeated.
(Tortora & Derrickson, 2009).
Mitosis is the most common form of cell replication seen as the vast majority of our cells are somatic. Mitosis is an important process as it provides new cells for growth, repair and replacement of older cells. (O'neill, 2010). Cell aging can also be known as cellular senescence. (Department of Pharmacology, 2010). This is a stage where the cells are no longer capable of dividing but remain metabolically actively. (Mayes, 2010).
The more specialized a cell type is, the less often it replicates. Less specialised cells such as those that protect the body replicate every 24 hours. (Loren, 1999). However, even though some are replication moreso than others, cell aging and death will effect each type of cells equally. Cells reach a limit of replication and do not continue to divide. This is when they reach cellular senescence, a dormant period. (Mayes, 2010).
As cells age, they become larger and are less able to reproduce. Cells loose ability to function and replicate as they normally would. (Dugdale, 2009).
Aging of all cells can change the structure and function of the cell and make it susceptible to disease and environmental stress. Aging does not effect normal cell replication in certain kinds of cells in the body such as skeletal muscle cells and nerve cells. Aging can slow down or stop processes vital to life. (Tortora & Derrickson, 2009). Some cells enlarge or die when they reach the end of their division. Cell replication is effected when cells are unable to build the apparatus that pulls apart chromosomes on the verge of division. (Shier, Butler & Lewis, 2007).
It can effect normal cell replication of muscle cells such as the hearth and lungs. This effects the immune system making it difficult to fight off disease. (Dugdale, 2009). As cells age, they may become mutated and undergo uncontrolled mitosis disallowing the cells to function properly. The reverse of this is where cells activate cell replication but are unable to control the rate. This is known to be associated with viral infections. (Loren, 1999).
Cells go through apoptosis throughout the lifetime of an organism. Apoptosis is another term for cell death. (Tortora & Derrickson, 2009). Cell death can cause trauma to the cell from normal physiological activities in an organism effecting cell replication. (Loren, 1999).
For example, hyperplasia occurs when the number of cells increases due to the increased role of all divisions. It can result in inflammation or disease. The increase in cell replication is due to cell death of other cells in an attempt to replace them. (Dugdale, 2009).
In some cell systems, cells have been found it exhibit enhanced cell replication but these cells also enhance apoptotic activity. Cells may then be eliminated by apoptosis. (Hermann, 2002). Most cells can only replicate a number of times where it reaches replicative senescence. This is its allocated number and the cell is unable to divide anymore. (Loren, 1999).
In conclusion, mitosis undergoes a type of cell division known as nuclear division. It duplicates its contents and divides into two to form new cells. Cell aging and death can cause cell replication to cease or to become overly active. (Tortora & Derrickson, 2009).
These can result in disease, inflammation, infection or it can have cancerous effects on the cells causing irregular cell replication.
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