The Effects of Smoking

Contents;
The following essay contains information pertaining to the biological effects of smoking. In particular it examines the effects of tar, nicotine and carbon monoxide on the respiratory and circulatory system. In addition to this it looks at some of the diseases linked with smoking, such as chronic bronchitis, emphysema, lung cancer and coronary heart disease; the latter of which is looked into in greater detail. The information for the essay, along with the statistics which are dispersed throughout, has been obtained from the point of referance cited at the end of the essay.

The Effects of Smoking;
Smoking kills around 114,000 people in the UK each year. Of these deaths, about 42,800 are from smoking-related cancers, 30,600 from cardiovascular disease and 29,100 die slowly from emphysema and other chronic lung diseases. Cigarettes contain more than 4000 chemical compounds, over 400 of these are toxic substances and at least 60 are known to be carcinogenic. These substances are taken into the body via the smoke that the smoker inhales, through the filter, and the smoke breathed in from the burning end; this smoke can also affect nearby non-smokers (termed passive smoking). It is thought that the most dangerous of the chemicals present are tar, nicotine and carbon monoxide.

Tar is a combination of chemicals, which settles on the lining of the airways and alveoli. Its presence can cause an allergic reaction, in which the smooth muscles in the walls of the airway contract; narrowing the lumen and thus restricting the flow of air to the alveoli. In addition to this the tar stimulates the goblet cells in the airway, to secrete more mucus; this traps viruses and bacteria as usual. However as the tar also paralyses or destroys the cilia that line the surface of the airway, preventing them from wafting layers of mucus to the back of the throat, the mucus collects in the airway; where the pathogens can multiply, blocking the bronchioles. This makes the lungs more susceptible to infection; meaning that smokers are more likely to catch diseases such as influenza or pneumonia. This is part of the reason why smokers take 25 per cent more sick days a year than non-smokers. Over time the continual irritation of the airways by these pathogens, leads to the smoker developing what is known as a smokers cough, this is the bodies attempt to remove the mucus from the lungs. However this has numerous detrimental side effects on the respiratory system. The delicate lining of the airways and alveoli can be damaged; this will then be replaced by scar tissue, which is thicker and has less elasticity. Whilst the layer of smooth muscle in the walls of the bronchioles thickens. This combination permanently narrows the lumen of the airway, further impeding the flow of air to the alveoli.

The recurring infections produced by the presence of bacteria and viruses in the mucus, inflames the lining of the airways; this damages the epithelium and attracts white blood cells to the area, to combat the pathogens. In order to get into the airways, they must leave the blood; they do this by releasing enzymes such as elastase, which digest parts of the lining of the lungs, allowing them to pass into the air spaces. This reduces the elasticity of the alveolus wall, so when we exhale they do not recoil pushing air out; thus the bronchioles collapse and this can cause the alveoli to burst as the pressure in the lungs increases. The above factors contribute to cause diseases such as chronic bronchitis, Emphysema and Chronic obstructive pulmonary disease which is a combination of the two. Furthermore tar is also known to contain the carcinogenic compound Benzopyrene (in the United States, 87% of lung cancer cases have been linked to smoking) and also damages the mouth by rotting, teeth, damaging gums and taste buds.

Nicotine and Carbon monoxide both enter the lungs, where they are quickly absorbed into the blood stream (within 30 seconds of entering the body nicotine reaches the brain); where they cause changes to the circulatory system, which lead to an increased risk of cardiovascular disease. This is shown by the fact that Smokers tend to develop coronary thrombosis 10 years earlier than non-smokers, and make up 9 out of 10 heart bypass patients. Nicotine is a highly addictive drug, but with repeated use, tolerance develops rapidly. For example, non-smokers can absorb (by tablet) only 4 mg of nicotine before symptoms of nausea, vomiting, diarrhoea and weakness begin. While the average smoker can tolerate twice as much nicotine, without any immediately noticeable effects. However Nicotine does have a variety of effects on the body. It mimics the action of transmitter substances, at the synapses between nerves, making the nervous system more sensitive and the smoker feel more alert. It stimulates the adrenal glands to release the hormone adrenaline; this increases the heart rate and breathing rate, and causes the constriction of the arterioles; together these raise the blood pressure in the arterioles. Nicotine also affects the platelets, making them sticky, increasing the risk that a blood clot or thrombus may form. Carbon Monoxide is a toxic gas (the gas that kills people when they commit suicide, by turning on their car engine and closing the garage door) which diffuses into red blood cells where it combines, more readily that oxygen, with haemoglobin, forming carboxyhaemoglobin. This reduces the amount of oxygen that can be carried in the blood, and heart rate may increase as a result of this. It also damages the lining of the arteries.

These changes all contribute to causing diseases such as coronary heart disease, roughly 120,000 people in the UK die each year from heart disease; making it the most common form of death in the UK. Coronary heart disease is caused by a build up of lipid plaques (often referred to as atheroma) on the inner walls of the coronary arteries that supply blood to the heart muscle, narrowing the vessel’s lumens. This is known as atherosclerosis. The development of arthrosclerosis is a response of the blood vessel to damage to the endothelial cells lining the lumen of the vessel by toxins such as carbon monoxide. Once the lining is damaged, cells known as foam cells enter the vessel and absorb the cholesterol and fat from the blood stream. Accumulation of foam cells forms a fatty streak on the side of the vessel; this is the earliest sign of arthrosclerosis. Next is the formation of intermediate lesions (a section of abnormal tissue) consisting of foam cells and lipid pools. Smooth muscle cells also gather at the site of plaque formation and die. Together these cells form fibrous plaques which often impede blood flow and can rupture; causing the blood to clot forming a thrombus, blocking the artery, or it can break free and be carried around in the blood until it reaches a narrow artery, where it will lodge, preventing blood flow through that artery. The chance of a thrombus forming is increased by the presence of nicotine; which makes the platelets sticky and thus more likely to clot and constricts the arterioles, making it easier for a clot to block them. The restriction of the blood supply and hence the supply of oxygen for respiration, caused by atherosclerosis, reduces the hearts ability to function and can lead to coronary heart disease in three forms; Angina, a severe pain in the chest which may extend down the left arm or up the neck, often experienced during exercise. A heart attack or myocardial infarction, the death of part of the heart muscle. Finally heart failure, when the heart cannot sustain its pumping action. It can also lead to a stroke. This occurs when the blood flow to part of the brain is lost, causing the death of a part of the brain tissue. If the thrombus blocks an artery leading to part of the brain or an artery leading the brain bursts (haemorrhages). However it should be remembered that coronary heart disease is a multifactoral disease, and that other factors such as age, sex and diet all contribute to the risk of a person developing CHD as well.

Ultimately it is quite clear, from the information above, that smoking cigarette’s increases the risks of an early death. This is supported by epidemiological data links; such as the fact that up to 50% of smokers may die of smoking-related diseases. One third of cancer deaths are as a result of cigarette smoking, and a quarter of smoker’s die of lung cancer. Chronic obstructive pulmonary disease is very rare in non smokers, less than 10% of victims are non-smokers, and less than 2% of people with emphysema are non-smokers. One fifth of smokers suffer from emphysema, and as a result deaths from pneumonia and influenza are twice as high amongst smokers.

References;
1.http://www.netdoctor.co.uk/health_advice/facts/smokehealth.htm

2.http://www.patient.co.uk/health/Smoking-The-Facts.htm

3.http://www.nlm.nih.gov/medlineplus/smoking.html

4.http://americanheart.mediaroom.com/index.php?s=43&item=897

5.http://ezinearticles.com/?Tar-Smoking---How-it-Works-in-Ruining-Your-Health&id=2362076

6.Ocr Biology for AS, by Pete Kennedy and Frank Sochacki, published by Heinemann.

By Marcus Ghosh