The Effects Of Smoking

Introduction
In the essay I will explore the contents of cigarettes while looking at the diseases that they can cause and how smoking links to those diseases.

Cigarette contents

Carbon Monoxide
Carbon monoxide is a colourless, odourless gas and is produced by the partial oxidisation of carbon containing compounds. Smokers are at an increased risk of carbon monoxide poisoning due to the cigarette smoke containing it. Carbon monoxide combines with the haemoglobin in the blood, displacing the oxygen meaning that less oxygen can be transported. The carbon monoxide that combines with haemoglobin to form COHb and this cannot be reversed back to oxyhaemoglobin. While smokers have a much higher level of COHb, non smoker’s levels can be high through second-hand smoke through smoking partners or friends. This is a reason why smokers are often associated with loss of breath during exercise. Exposure to carbon monoxide could lead to fatigue, vomiting and mental confusion. It is harmful at any level and can kill you, long term exposure of lower levels can cause heart problems.

Tar
Tar a brown substance which is left behind after a cigarette. It is the reason why smokers characteristically have yellowy brown teeth and fingers. The tar also paralyses the cilia in our airways preventing them from sweeping mucus and bacteria out of our throats preventing infect. The paralysis of the cilia causes lung diseases such as emphysema, bronchitis and lung cancer. The tar coats your lungs with a layer which for an average 20 a day smoker could fill up a 210ml cup full of tar. Tar can be deposited in the bronchiole tube blocking them up near to the air sac. This causes the smoker to cough in order to try and remove the blocked bronchioles. The constriction of the airways is another reason why smokers have difficulty breathing. When the lungs can’t clear the tar out of the air sacs the air sacs can collapse. When the collapse the tar can be cleared out and after this occurs they can reinflate. However, when this is a regular occurrence sometimes the walls of the alveoli will fuse with the walls of other alveoli. This decreases the surface area, which reduces the area for gaseous exchange to occur causing emphysema.

Nicotine
Nicotine as well as being the substance smokers get addicted to is also a vasoconstrictor. It is believed that Nicotine is as addictive as heroin or cocaine which explains why people become so addicted. The nicotine travels in your bloodstream and can reach ones brain in 10 seconds, giving the smoker an instant effect of euphoria. Nicotine has an average half life of around 40 minutes. This means after this smokers feel the urge to have another cigarette. This means that it reduces the diameter of the blood vessels while present in the blood. This puts an additional strain on the heart as it has to pump harder to get blood through the body. The constriction of the airways means that it reduces gaseous exchange. It is also thought that nicotine also paralyses cilia as well as tar. Nicotine stimulates the adrenal glands to release the hormone adrenaline.

Cardiovascular disease

Cardiovascular disease is defined as any disease that affects the circulatory system, including the heart and blood vessels. Smoking is one of the main causes of cardiovascular disease specifically chronic heart disease. Smoking causes the levels of fibrinogen causing the blood to clot, making the blood thicker. Studies have shown that smokers have a 50% higher chance of getting CHD than non smokers, 75% in heavy smokers and mortality from any cardiovascular disease is 60% higher in smokers than non smokers and in heavy smokers this is as much as 85% higher. This is why cardiovascular disease is the second biggest killer from smoking in the UK.

Atherosclerosis
Carbon monoxide and high blood pressure can cause serious damage to the endothelium. This damage is repaired by the action of the phagocytes which encourages the growth of a layer of smooth muscle and the deposition of fatty substances. The deposits otherwise known as atheromas include cholesterol from low density lipoproteins, fibres, dead blood cells and platelets. The process of deposition is called atherosclerosis. Atheromas can eventually lead to a build up of plaque in the lumen of the artery, meaning that reduces blood flow but also it makes the artery less flexible and leaves the walls a lot rougher than that of a healthy artery.

Thrombosis
Blood flowing past the plaque which has been built up through atherosclerosis cannot flow as smoothly increasing the chances of it clotting. Nicotine is a big contributor to this as it causes the platelets to become ‘sticky’ which increases the chance that the blood will stick. The plaque is covered with a thin, delicate membrane which if ruptured causes the red blood cells to also stick to the plaque. This causes the blood to clot, and a clot is called a thrombus. Clots in arteries are very dangerous and is potentially life threatening. The clot reduces the lumen but more serious damage occurs when part of the clot breaks off and lodges itself in a narrower artery preventing blood flow through it.

Coronary Heart Disease
The heart has its own supply of blood through the coronary artery which is branched off the aorta. The blood travels through it at a high blood pressure and is at risk of atherosclerosis. A build up of plaque of thrombosis in the coronary artery can lead to a lack of blood flow to the heart and therefore the heart receives an inadequate supply of oxygen which is need for respiration. This can lead to coronary heart disease which can be in the form of angina, myocardial infarction (heart attack) or heart failure. Angina is a severe chest pain which may spread up your neck and down your left arm, it is often confused with myocardial infarction. Myocardial infarction however is the death of the heart muscle usually caused by a thrombosis (clot) in the coronary artery. This blocks blood and oxygen getting to the heart muscle. Finally heart failure is when the heart has problems pumping blood due to a blockage in the coronary artery.

Stroke
A stroke is the death of part of the tissue in the brain. It is caused by a loss of blood flowing to the brain and is caused in two ways. The first is by part of a thrombus breaking and getting stuck in a smaller artery leading to the brain preventing any blood flowing to it. Secondly and artery which is leading to the brain bursts, this is called a haemorrhage.

Evidence Linking Smoking To Diseases
Studies done across the world in countries such as Japan and USA have shown us that 9 out of every 10 cases of lung cancer are due to smoking. IN 2002, 33,600 people were killed due to lung cancer meaning roughly 4 an hour died because of it. It was first discovered that smoking caused lung cancer in 1950 when a study found that people smoking between 15 and 24 cigarettes a day were 26 times more likely to have lung cancer than people who didn't smoke. Even people smoking less than 15 a day still were 8 times more likely to develop lung cancer. However it’s not just lung cancer that smoking can cause. It also contributes towards bladder, cervix, kidney, larynx (voice box), mouth, oesophagus , pancreas, stomach, liver and some types of leukaemia. Smokers are 7 times more likely to die of cancer than non smokers. The reason for all these cancers being caused is due to the poisons in the cigarettes. Benzene is a known cause of leukaemia and one study suggests that it can be accounted for 10 – 50% of the deaths due to leukaemia.
 
Reference
http://www.carbonmonoxidekills.com/carbon_monoxide_in_cigarettes.htm
http://quitsmoking.about.com/b/2006/06/20/tar-in-cigarettes.htm
http://www.allsands.com/health/smokingeffects_srw_gn.htm
http://www.heartstats.org/datapage.asp?id=3851
http://info.cancerresearchuk.org/healthyliving/smokingandtobacco/howdoweknow/
OCR Biology AS Frank Sochacki and Peter Kennedy

By Alexander Ewing