Attracting Abundance
- 108 -
The Law
Belief - XX
Our Cellular Biology - XIX
Our Cellular Biology - XIX
I will devote this concluding post on cellular biology to tissues.
As mentioned earlier, tissues are organized communities of cells that work together to carry out a specific function. The type of cells present in the tissues determine the function of the tissue. For example, the endothelial tissue that lines the human gastrointestinal tract consists of several cell types. Some of these cells absorb nutrients from the digestive contents, some secrete a lubricating mucus that helps the contents travel smoothly.
Without cell division, long term tissue survival would not be possible. Inside tissues, cells are constantly replenishing themselves through the process of division, although the rate of turnover may vary widely between different cell types in the same tissue. Neurons are not the only cells that lose their ability to divide as they mature, the same is true for some differentiated cells as well. To counteract this loss, tissues maintain stem cells to serve as a reservoir of undifferentiated cells.
Note: A differentiated cell is a cell that is performing a specialized task in an organism like a liver cell, a blood cell, neuron etc.There re more than 250 general types of cells within a human body. the process of differentiation occurs in embryonic stage itself, when decisions are made as to which gene in a cell is expressed and therfore what type of cell will result.
Note: Stem cells are undifferentiated cells. They can divide, through mitosis, to produce more stem cells, even after long periods of inactivity, and help in repairing damages tissues. They can also differentiate into different types of specialized cells. When a stem cell divides, each new cell retains the potential of either dividing into more stem cells or differentiating into a specialized cell. In some groups, such as the gut and the bone marrow stem cells regularly divide to repair and replace worn out or damaged tissues. In other organs, however, such as the pancreas and the heart, stem cells only divide under special conditions
Whenever stem cells are called upon to generate a particular type of cell, they undergo an asymmetric cell division. In asymmetric cell division, each of the two daughters has an unique life course. In this case, one of the daughter cells has a finite capacity for cell division and begins to differentiate., whereas the other daughter cell remains a stem cell with unlimited proliferative ability.
Although most of the tissues in adult organism maintain a constant size, the cells that make up these tissues are continuously turning over. Therefore, for a particular issue to stay the same size, its rate of cell death and cell division must remain in balance.
The tissue structure is supported not only by the balance between cell death and division, but also by the cell junctions and cytoskeletal structure which help stabilizing the cell structure. For example, the cells that make up the human epithelial tissue attach to one another through several types of adhesive junctions. Some specific trans-membrane proteins provide the basis for such adhesive junctions. At these junctions, specific trans-membrane proteins on one cell interact with similar trans-membrane proteins on the adjacent cell, Special adapter proteins then connect the resulting assembly to the cytoskeleton of each cell. The many connections formed between junctions and cytoskeletal proteins effectively produces a network that extends over many cells, providing mechanical strength to the epithelium.
Whenever stem cells are called upon to generate a particular type of cell, they undergo an asymmetric cell division. In asymmetric cell division, each of the two daughters has an unique life course. In this case, one of the daughter cells has a finite capacity for cell division and begins to differentiate., whereas the other daughter cell remains a stem cell with unlimited proliferative ability.
Although most of the tissues in adult organism maintain a constant size, the cells that make up these tissues are continuously turning over. Therefore, for a particular issue to stay the same size, its rate of cell death and cell division must remain in balance.
The tissue structure is supported not only by the balance between cell death and division, but also by the cell junctions and cytoskeletal structure which help stabilizing the cell structure. For example, the cells that make up the human epithelial tissue attach to one another through several types of adhesive junctions. Some specific trans-membrane proteins provide the basis for such adhesive junctions. At these junctions, specific trans-membrane proteins on one cell interact with similar trans-membrane proteins on the adjacent cell, Special adapter proteins then connect the resulting assembly to the cytoskeleton of each cell. The many connections formed between junctions and cytoskeletal proteins effectively produces a network that extends over many cells, providing mechanical strength to the epithelium.
With this I shall conclude the series of posts that explain cellular biology in simple terms. I had mentioned earlier that, a basic understanding of cellular biology would be very helpful on understanding the effect of belief, happiness and other emotions on our body and our environment, scientifically.
However a last part on a subject that may be interesting to understand is the phenomena of cancerous cells. I clarify that this has no relation to our subject of discussion. The following discussion is only to serve a limited purpose of gaining some insight into the phenomena of cancer.
Cancer cells are cells that do not respond to the signals that control replication and death of cells. Cancer cells originate within tissues and, as they grow and divide, they diverge ever further from normalcy. Over time, these cells become increasingly resistant to the controls that maintain normal tissues, and as a result they divide more rapidly than their ancestors and become less dependent on signals from other cells. Cancer cells even evade programmed cell death, despite the fact that their multiple abnormalities would normally make them prime targets for apoptosis. In the late stages of cancer, cells break through normal tissue boundaries and spread (metastasize) to new sites in the body.
In normal cells, hundreds of genes intricately control the process of cell division. Normal growth requires a balance between the activity of those genes that promote cell proliferation and those that suppress it. It also relies on activities of those genes that signal when damaged cells should undergo apoptosis. In simpler terms, a cell is continuously receiving messages from its own genes and from other cells - some message tell the cell o grow and multiply, other messages tell it to stop growing and rest, or even to die. If there are enough "grow" messages, the next stage of cell's life starts. In a cancer cell, the messages to grow may be altered, or the messages to stop growing or apoptosis may be missing. The cell then starts growing uncontrollably and divide too often.
Every time a normal cell divides, the ends of its chromosomes - telomeres - becomes shorter. Once they have worn out, the cell dies and is replaced. The cancer cells heat this system - they retain their long chromosomes by continuously adding bits back on. This allows the cancer cells to live forever. The cells from the body of Henerietta Lacks, an American woman who was detected with cervical cancer, are still growing.
Most normal cells in your tissues stay put, stuck to each other and their surroundings. Unless they are attache to something they can not grow and multiply. If they become detached from their neighbors, they commit suicide by the process called apoptosis. But in cancer cells the normal self-destruct instructions do not work, and they can grow and multiply without being attached to anything. this allows them to invade the rest of the body, travelling via the bloodstream to start more tumors elsewhere (metastasis)
Cells become cancerous after mutations (a sudden departure from the parent type in one or more heritable characteristics) accumulate in the various genes that control cell reproduction. According to research, most cancer cells possess 60 or more mutations but many of the mutations may not have anything to do with cancer growth. Different kinds of cancers have different mutational signatures. Certain genes, like the growth-promoting genes, are mutated in cancer cells more often than the others. Some cancer-related mutations may inactivate the genes that suppress cell reproduction or those that signal the need for apoptosis.
Every time a healthy human cell divides, it copies all its genes, which are bundled into 46 chromosomes. This process has several checkpoints to to ensure that each new cell gets a near-perfect copy.But in a cancer cell these checkpoints are often missing. The result is a chaos - parts of chromosomes may be lost, rearranged or copied many times and the genes are more likely to acquire further mutations.
All the cells usually work together as a community. But if a cell acquires a gene mutation that makes it multiply when it should not, or helps it survive when it should have died, it has an advantage over the others. Eventually, the abnormal cells acquire mutations in more genes, causing uncontrolled growth. These abnormal cells have a complete advantage as they produce more off springs than the normal cells and thus have better chances of survival.
In normal cells, gene damage is usually quickly repaired. If the damage is too severe, the cell is made to die. An important protein called p53 checks for gene damage in normal cells, and kills them if the damage if found to be too great to repair. However, in cancer cells p53 itself may be defective, which does not work properly, allowing cancer cells to survive.
I conclude with a diagram explaining the stages of cancer growth.
Namaste
Till we meet again
Prabir
However a last part on a subject that may be interesting to understand is the phenomena of cancerous cells. I clarify that this has no relation to our subject of discussion. The following discussion is only to serve a limited purpose of gaining some insight into the phenomena of cancer.
Cancer cells are cells that do not respond to the signals that control replication and death of cells. Cancer cells originate within tissues and, as they grow and divide, they diverge ever further from normalcy. Over time, these cells become increasingly resistant to the controls that maintain normal tissues, and as a result they divide more rapidly than their ancestors and become less dependent on signals from other cells. Cancer cells even evade programmed cell death, despite the fact that their multiple abnormalities would normally make them prime targets for apoptosis. In the late stages of cancer, cells break through normal tissue boundaries and spread (metastasize) to new sites in the body.
In normal cells, hundreds of genes intricately control the process of cell division. Normal growth requires a balance between the activity of those genes that promote cell proliferation and those that suppress it. It also relies on activities of those genes that signal when damaged cells should undergo apoptosis. In simpler terms, a cell is continuously receiving messages from its own genes and from other cells - some message tell the cell o grow and multiply, other messages tell it to stop growing and rest, or even to die. If there are enough "grow" messages, the next stage of cell's life starts. In a cancer cell, the messages to grow may be altered, or the messages to stop growing or apoptosis may be missing. The cell then starts growing uncontrollably and divide too often.
Every time a normal cell divides, the ends of its chromosomes - telomeres - becomes shorter. Once they have worn out, the cell dies and is replaced. The cancer cells heat this system - they retain their long chromosomes by continuously adding bits back on. This allows the cancer cells to live forever. The cells from the body of Henerietta Lacks, an American woman who was detected with cervical cancer, are still growing.
Most normal cells in your tissues stay put, stuck to each other and their surroundings. Unless they are attache to something they can not grow and multiply. If they become detached from their neighbors, they commit suicide by the process called apoptosis. But in cancer cells the normal self-destruct instructions do not work, and they can grow and multiply without being attached to anything. this allows them to invade the rest of the body, travelling via the bloodstream to start more tumors elsewhere (metastasis)
Cells become cancerous after mutations (a sudden departure from the parent type in one or more heritable characteristics) accumulate in the various genes that control cell reproduction. According to research, most cancer cells possess 60 or more mutations but many of the mutations may not have anything to do with cancer growth. Different kinds of cancers have different mutational signatures. Certain genes, like the growth-promoting genes, are mutated in cancer cells more often than the others. Some cancer-related mutations may inactivate the genes that suppress cell reproduction or those that signal the need for apoptosis.
Every time a healthy human cell divides, it copies all its genes, which are bundled into 46 chromosomes. This process has several checkpoints to to ensure that each new cell gets a near-perfect copy.But in a cancer cell these checkpoints are often missing. The result is a chaos - parts of chromosomes may be lost, rearranged or copied many times and the genes are more likely to acquire further mutations.
All the cells usually work together as a community. But if a cell acquires a gene mutation that makes it multiply when it should not, or helps it survive when it should have died, it has an advantage over the others. Eventually, the abnormal cells acquire mutations in more genes, causing uncontrolled growth. These abnormal cells have a complete advantage as they produce more off springs than the normal cells and thus have better chances of survival.
In normal cells, gene damage is usually quickly repaired. If the damage is too severe, the cell is made to die. An important protein called p53 checks for gene damage in normal cells, and kills them if the damage if found to be too great to repair. However, in cancer cells p53 itself may be defective, which does not work properly, allowing cancer cells to survive.
I conclude with a diagram explaining the stages of cancer growth.
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| Stages of tumour growth to malignant stage (curtsey: NCBI) |
Namaste
Till we meet again
Prabir
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