Cancer describes a disease characterised by uncontrolled growth of cells typically resulting in a tumour (except in the case of leukaemia). Such a disease arises once genes suffer a sufficient number of changes and mutations so as to disrupt cell growth. Age is the single biggest factor for cancer – two thirds of all cases of cancer are in the over 65s because the longer an individual is alive, not only are they exposed to more factors that lead to genetic mutations, but individual’s become less able to correct any mistakes made.

Normal cells have their growth regulated by contact inhibition of movement, density dependent inhibition of growth, adhesiveness, anchorage dependence and growth factors. Cancerous tumours grow in spite of these “regulations” and their growth is dependent upon tumour growth rate (how quickly old cells are replaced by new cells), having an adequate blood supply and in the case of hormone-linked tumours, having an adequate level of hormones.

However, an abnormal cell and a tumour is not indicative of cancer. A neoplasm or “new growth” is an abnormal growth that is no longer subject to normal homeostatic controls. A neoplasm may be benign or malignant; a benign tumour occurs when a neoplasm develops in a restricted space, where they metabolise and mature normally and are rarely fatal. Schwannoma are benign growths that form from the Schwann cells of nerves. The tumours themselves are not fatal, however if they grow to a sufficient size they may result in nerve compression or damage, ischemia or necrosis. A malignancy is unable to perform specific tasks, an infinitive proliferative lifespan, uncontrolled metabolism and a high nutrient demand.

There are 5 main differences between benign and malignant tumours: Benign tumours are usually encapsulated, malignant ones are not; benign tumours have a low mitotic rate, malignant tumours have a high one; benign tumours are well differentiated, malignant ones are not; benign tumours are unable to be invasive or metastasise unlike malignant tumours.

The metastasis of a malignant tumour is the development of secondary tumours originating from the original malignancy in a new location. This may occur from part of the tumour breaking off into the local area where it may be transported to another part of the body in the lymph or blood; where in the latter case the malignant cell(s) move in and out of the blood vessel by intravasation and extravasations.

Malignant tumours or cancer are the result of an accumulation of genetic mistakes for which there are several risk factors asides age including diet, hormones, UV exposure, family history and smoking. Salt is thought to irritate the lining of the stomach, leading to inflammation and creating conditions where mutations may arise; red meat contains nutrasamines, which are carcinogenic. On the other hand, caretenoids, antioxidants, flavanoids, phytochemicals and fibre are considered beneficial constituents of diet. Natural hormone levels change over time and lead to an increase in certain cancers at certain ages; encochrone-disrupting chemicals are found in pesticides and mimic the effects of hormones increasing the incidence of hormone-related tumours. Excessive UV exposure can cause genetic mutations to DNA that can lead to skin cancer. Some tumours have a very strong genetic link, for example BRCA and breast cancer and S100 and benign scwannoma. Finally smoking has a strong association with cancers. As well as the pathological effects smoking has not associated with cancer (cecreaseing haemogloban availablility to oxygen) the smoke paralyses the cilia in the respiratory tract and eventually (reversible) squamous metaplasia takes place replacing the epithelial cells. This may lead to further changes to the cell including size and number, known as dysplasia (or precancer). Further damage can lead to cancer.

If this cancer occurs on the epithelium, the result is a carcenoma

	Criado por Sami-Jaine aproximadamente 11 anos atrás

BSc (Hons) Biology Notas sobre Not finished as I got bored - might be helpful however? xxx, criado por Sami-Jaine em 13-05-2013.