UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes re-edit 17/05/2023 [SEARCH]

 Non-communicable diseases: 3. Cancer - many types and many risk factors!

Doc Brown's biology exam revision study notes

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There are various sections to work through,

 after 1 they can be read and studied in any order.

INDEX of notes on non-communicable diseases

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(3) Cancer - a non-communicable disease - many types and many risk factors!

What is cancer?

Cells normally grow and divide by mitosis when the body needs new cells to replace old or damaged cells.

Cancer is caused by some genetic fault or change e.g. caused by a mutation, that leads to uncontrolled growth by cell division - these are known as cancerous cells and the body does NOT need them!

The extra mass of cancerous cells formed is called a tumour.

Most tumours are solid, but cancers of the blood like leukaemia are obviously not.

Tumours can be benign (non-cancerous) and not usually dangerous, or malignant (cancerous) which are potentially very harmful.

Benign tumours grow slowly and fill the space available.

A benign tumour stays in one place e.g. in a membrane and often has a capsule around it making it quite easy to remove surgically.

Benign tumours are not cancerous and the cancer cells do not invade other tissues of the body.

Because they are not cancerous, benign tumours are not usually harmful or dangerous to the body - but may be removed to stop the cancer from becoming malignant.

Malignant tumors keep growing faster then benign tumours, and spread to neighbouring healthy tissue.

Malignant cells can break away and spread to other parts of the body in the bloodstream.

* The same malignant cells can then invade healthy tissue and form secondary tumours in other parts of the body.

Therefore malignant tumours are highly dangerous forming potentially fatal cancers.

* As the malignant cells replicate they can invade surrounding tissue. Unfortunately, this malignant tumour can secrete hormone-like chemicals that stimulate blood vessels to grow around the tumour and supply it with food and oxygen so the cancerous cells further increase in number. Malignant cells can detach from the tumour and be transported away in the bloodstream. These malignant cells can 'squeeze' through a capillary wall and produce a secondary tumour in a different tissue.

For more on cell division see

Cell division - cell cycle - mitosis, meiosis, sexual/asexual reproduction, binary fission and cancer 

Risk factors associated with types of cancer

A large proportion of our ever increasing aging population will eventually suffer from cancer.

300 000 people are diagnosed with cancer in the UK every year, but it is estimated that 4 in 10 cases are preventable by making suitable lifestyle choices, and the earlier these choices are made the better!

We can get a cancer at any stage in our life, though as we get older our defensive immune system does decline in response to threats.

Cancer survival rates are continually increasing, particularly in richer developed countries with their comprehensive health care services, including early diagnosis from screening programmes and improved anti-cancer treatments.

Carcinogens

A carcinogen is defined as a chemical substance or other agent capable of causing cancer in living tissue - usually a chemical that promotes changes in the structure and working of cell DNA.

e.g. chemicals in the home, industry or in the environment, ionising radiation e.g. from radioactive materials, lifestyle choices e.g. alcohol drinking or poor diet, ultraviolet radiation from over exposure to sunlight, viruses like HPV. More on these in the following notes.

A carcinogen causes cancer by damaging the DNA - that is causing a mutation in one or more of the chromosomes in the cells genome,

Mutations can occur by chance as cells are dividing, though most of these are not damaging because genetic errors are checked for in the cell cycle and repairs put in place!

Generally speaking you need several mutations to cause cancer cells to develop, which is why we become more susceptible to cancer as we get older - the repair systems become less effective!

Industrial practice and bad lifestyle habits have been responsible for some of the more common cancers in the past, particularly in men, but now we know more about the causes, things are improving for future generations e.g.

Sheets of the mineral asbestos were widely used in housing and factories for thermal insulation. Unfortunately, very fine asbestos fibres build up in the air passages of lungs. All forms of asbestos increase the risk of lung disease. The three types of asbestos-related lung disease are scarring (asbestosis), non-cancerous disease of the tissue of the lining of the surface of the lung (pleural disease), and lung cancer (of the lungs or their outer lining tissue - mesothelioma).

Several molecules in tobacco tar are carcinogenic, which you breathe down into your lungs when smoking.

Genetics - inheritance and mutations

Unfortunately, you can inherit faulty genes that make a person more susceptible to cancer.

Mutations in the BRCA genes have been linked to increased chance of women developing breast cancer or ovarian cancer - a good reason and argument for cancer screening programmes e.g. cervical smear test for cervical cancer or x-ray screening for breast cancer.

Ionising radiation - a powerful carcinogenic agent

Exposure to ionizing radiation - uv, x-ray or gamma radiations, causes cell damage leading to cancer.

Ionising radiation is therefore described as carcinogenic.

Diet factors

Obesity - being overweight, is now being linked to cancers of the bowel, kidney and liver.

Too much fat and sugar in you diet is not good for your, excess calories the body doesn't need are converted into fat tissue.

Apparently, statistically, it is the 2nd biggest preventable cause of cancer, the 1st is smoking!

Osteoporosis

Osteoporosis a medical condition in which the bones become brittle and fragile from loss of tissue, typically as a result of hormonal changes, or deficiency of calcium or vitamin D in your diet.

Meat

Too much red meat and processed meat in you diet is linked to an increase risk of bowel cancer.

Regular aerobic exercise can reduce your risk from some non-communicable diseases.

See the Keeping healthy - diet and exercise 

and Respiration - aerobic and anaerobic in animals 

doc b oil notesSmoking - chemicals in tobacco smoke are carcinogenic.

Giving up smoking, is a lifestyle choice to reduce your chance of developing lung cancer.

Statistically, stopping smoking is the biggest preventable cause of cancer.

There is clear evidence of a link between smoking and contracting lung cancer.

(Its a 'no-brainer' for me, and admit to smoking cheap nasty cigarettes from the age of 11 to 27!).

However, that's not the only cancer risk from smoking - it is being linked cancers in the cervix, bowel, mouth and stomach.

Ultraviolet light (uv) is a powerful carcinogenic agent.

The more uv light you are exposed too, including bright sunlight, the greater the chance developing skin cancer - uv damages skin cells including burns or causing mutations in the skin cell DNA.

Ultraviolet radiation is used to irradiate sun-beds, so frequent users of sun beds are also increasing their risk of skin damage - the lamps emit uv radiation which can cause DNA damage leading to cancer.

People who work outside or live in particularly sunny climates, are at higher risk - though evolution has allowed many people to have developed extra melanin in their skin to increase uv protection - that's why so many people in sunny areas like Africa have a much darker skin than many northern European peoples.

Fair-skinned should use sun-blockers to protect their skin in bright sunlight.

Viruses

Some types of cancer are triggered by particular viral infections. See also Communicable diseases

This is a communicable disease causing an increase in the likelihood of developing a non-communicable disease.

The hepatitis virus (hepatitis B and C strains) causes long-term infections in the liver where it inhabits the cells and this gives you an increased chance of developing liver cancer.

The chance of becoming infected with this communicable disease can depend on your lifestyle e.g. contracting hepatitis during unprotected sex or drug users sharing a needle.

The human papillomavirus (HPV virus) is a virus that can infect the human reproductive system.

HPV is a communicable pathogen infection, BUT, is linked to non-communicable diseases.

HPV infection occurs when the virus enters your body, usually through a cut, abrasion or small tear in your skin. The virus is transferred primarily by skin-to-skin contact. Genital HPV infections are contracted through sexual intercourse, anal sex and other skin-to-skin contact in the genital region.

It is thought that most cases of cervical cancer arise from HPV infections - one disease causes another.

The HPV virus causes cervical warts.


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