CANCER
• Cancers are a result of uncontrolled mitosis.
• There are more than a hundred different forms of cancer.
• Lung cancer is the most common form of cancer in men while breast cancer in women.
• Cancerous cells divide repeatedly, out of control and a tumour develops which is an
irregular mass of cells. The cells usually show abnormal Changes in Shape.
• Cancers start when changes occur in the genes that control cell division.
• The particular term for a mutated gene that causes cancer is an oncogene.
• A factor which brings about any mutation is called a mutagen. If this mutagen is cancer causing then it is carcinogen/carcinogenic.
• Some of the factors, which can increase mutation rates are:
a) Ionizing Radiation: This includes X-rays, gamma rays and particles from the decay of radioactive elements. They cause the formation of damaging ions inside cells, which can break DNA strands. Ultraviolet light can also damage the genes. Due to depletion of the ozone layer, more ultraviolet light is penetrating to the Earth's surface and could result in an increase in cases of skin cancer.
b) Chemicals: Many different chemicals are carcinogenic (e.g tar of tobacco smoke).All these chemicals Damage DNA molecules.
c) Virus Infection: Some cancers in animals/humans are by viruses.
d) Hereditary tendency: Cancer is more common in some families than others indicating a genetic link. The disease itself is not inherited but the factors that cause the disease are inherited.
Basic Types of Tumours:
i) Benign tumours: These do not spread from their site of origin, but can compress and displace surrounding tissues, for example warts, ovarian cysts and some brain tumours.
ii) Malignant (cancerous) tumours: These are far more dangerous since they spread throughout the body invade other tissues and ultimately destroy them. Malignant tumours interfere with the normal functioning of the area where they have started to grow. They may block the intestines, lungs or blood vessels. Cells can break off and spread through the blood and lymphatic system to other parts of the body to form secondary growths. The spread of cancers in this way is called metastasis. It is the most dangerous characteristic of cancers.
Characters of Cancer Cells:
o Cancer cells can be distinguished from normal cells because they are less differentiated than normal cells.
Similarly they show the characters of rapidly growing cells, for example high nucleus to cytoplasm ratio prominent nucleoli and many mitosis.
o The presence of invading cells in otherwise normal tissue is an indication of malignancy.
Causes of Cancer:
Cancer is caused mainly by mutations in the somatic cells. The cancer results from the accumulation of as few as three to as many as twenty mutations, in genes that regulate cell division.
These mutations bring two basic changes in the cancer cells.
i) First the metastatic cells break their contact with other cells and overcome the
restrictions on cell movement provided by basal lamina and other barriers.
Ultimately metastatic cells can invade other parts of the body.
ii) Secondly: they proliferate, unlimitedly, without minding the checks or programmes of the body.
Nucleus, structure and composition of nucleus
Very important topic to be discussed
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