How do these substances in cigarettes cause harm?Watch
Tanx, I will give reps to best answers
Tar is a mixture of different compounds.
Tar builds up in the lungs. This causes gaseous exchange to occur less effectively as it increases diffusion distance in the alveoli.
The tar paralyses ciliated epithelial cells, stopping them from functioning. It also causes goblet cells to overproduce mucus. The affect of these two effects is that mucus builds up in the airways. This has several effects:
In the long term, mucus not being removed effectively can cause lung infections as bacteria are more likely to thrive in the lungs.
It can cause a smoker's cough as the body attempts to move the mucus mechanically.
Linked from mucus paragraph, a smoker's cough can damage the linings of the airways and alveoli. The linings are replaced by scar tissue and the smooth muscle becomes thicker and stronger. This makes the lumen of the airways thicker. In the long term a smoker's cough leads to chronic bronchitis, an inflammation of the airways, with an overproduction of mucus.
Linked from mucus paragraph, lung infections can damage the linings of the airways and alveoli. It also causes neutrophils to leave the blood and enter the airways to destroy the infection. To get from the blood to the airways, they need to get through the elastic tissue. To do this, they use the enzyme elastase to break down the elastic tissue. This causes permanent damage to the elastic tissue. The neutrophils then kill the bacteria via phagocytosis. The damage to the elastic tissue makes the airways less elastic and more stiff. The loss of elasticity is called emphysema. This, coupled with a smokers cough makes it likely that alveoli will burst. When this occurs, larger alveoli grow back in their place. These have a smaller surface area to volume ratio, so are less effective in gas exchange. This causes shortness of breath.
The tar can also cause allergic reactions, causing the smooth muscle to contract, causing bronchioles to constrict and hence breathing becomes difficult.
The tar contains carcinogens. When it builds up in the lungs, it can cause mutations which lead to cancer forming. This is generally at the fork between the bronchi, where most of the tar is deposited.
That's tar done. I'll do the others in a bit.
It causes addiction by affecting the nervous system.
It causes the release of adrenaline. This raises heart rate and causes vasoconstriction. These two effects raise blood pressure in arteries and arterioles. The increase of blood pressure can damage the walls of the blood vessels.
Nicotine causes vasoconstriction in the arterioles in the extremities of the body. This reduces blood flow to the extremities, which can have harmful effects.
It also causes the platelets to become more sticky. This increases the chance of a blood clot or thrombus forming.
Carbon monoxide enters the erythrocytes and bonds to haemoglobin forming carboxyhaemoglobin. Haemoglobin has a higher affinity for carbon monoxide than for oxygen, so the haemoglobin is permanently bonded to the carbon monoxide. This reduces the capability of the blood to carry oxygen.
Carbon monoxide can damage the walls of arteries.
I will now go into more detail on the long term effects of some of the impacts of these molecules. Some of the impacts of CO and nicotine overlap, so it makes sense to go into detail now rather than before.
Damage to the arteries:
This damage is repaired by phagocytes. This repair, however encourages more smooth muscle to be grown and fatty substances to be deposited (low density lipoproteins). These deposits are atheromas and the disease is atherosclerosis.
When it has grown sufficiently, the atheroma forms a plaque, which sticks out into the lumen of the artery. This reduces the lumen, so reduces blood flow. The atheroma also increases the friction to the blood, meaning that the heart has to work harder, which increases blood pressure. It also makes the walls less elastic, which makes them less able to stretch and recoil as they should to regulate pressure.
Atherosclerosis can also lead to arteriosclerosis, which is when minerals are deposited into the atheroma, causing the artery walls to become more inelastic, increasing the problems associated with atherosclerosis.
The atheroma can cause blood to clot around it. Nicotine increases the stickiness of platelets, which increases this chance.
The blood clot is called a thrombus. It will reduce blood flow in the artery. The thrombus can break free of the artery wall and move along the artery. It can then get stuck further along, completely stopping blood flow. if this happens in the brain, it will cause a stroke. If it happens in the heart, it will cause a myocardial infarction.
You should read the pages on tar, nicotine, CO and CHD.
The way I found easiest for this was to draw out a branching flowchart for each compound. Put down the effects of the compound, then on the next level link these to the effects that these can cause and so on.
So for example for tar, on the first level you'd have gaseous exchange is reduced due to tar building up, tar paralyses epithelial cells, tar causes allergic reactions, tar causes mutations. Then on the next level you'd link the secondary effect, for example the epithelial cells being paralysed causes a smoker's cough and also causes infections. The mutations cause lung cancer. Then the smoker's cough and infections would have a third and maybe a fourth level.