biology4alevel600

1 Tobacco smoke contains tar, carbon monoxide and  nicotine.  2 Tar settles on the epithelium lining the bronchi and  bronchioles and stimulates inflammation, an increase  in the secretion of mucus and an accumulation of  phagocytes from the blood.  3 Damage to the airways and alveoli occurs in chronic  obstructive pulmonary disease (COPD). In chronic  bronchitis, the airways are obstructed by mucus  and infection; in emphysema, alveoli are destroyed,  reducing the surface area for gas exchange.  4 Tar contains carcinogens, which cause changes in  DNA in bronchial epithelial cells, leading to the  development of a bronchial carcinoma. This is lung  cancer. 5 Some of the signs and symptoms of COPD are  breathlessness, wheezing and constant coughing;  two of the symptoms of lung cancer are coughing up  blood and chest pains.  6 Carbon monoxide combines irreversibly with  haemoglobin, reducing th...

Smoking  is one of the major avoidable  risk factors of chronic,  life-threatening diseases of the gas exchange and circulatory systems. The smoke from cigarettes contains several substances that affect the gas exchange system and the cardiovascular system. These include: • tar , a mixture of substances including various chemicals that act as carcinogens. • nicotine , an addictive substance that affects the nervous system by binding to receptors on neurones (nerve cells) in the brain and other parts of the body. It increases the release of a neurotransmitter called dopamine in the brain, which gives feelings of pleasure. It increases the release of adrenaline into the blood, which in turn increases breathing rate and heart rate. There is also some evidence that nicotine increases the likelihood of blood clots forming. • CO , which combines irreversibly with Hb, forming carboxyhaemoglobin. This reduces the amount of Hb available to combine with O 2 , and so reduces t...

1 Multicellular organisms often have surfaces that are  specialised to allow exchange of gases to take place  between their bodies and the environment. Alveoli in  the lungs form the gas exchange surface in mammals.  2 In the human lungs, air passes down the trachea and  through a branching system of airways to reach the  alveoli. The airways are lined by a ciliated epithelium  with mucus-secreting goblet cells. The epithelium  protects the alveoli by moving a carpet of mucus towards the throat, where it can be swallowed.  3 There are C-shaped rings of cartilage in the trachea  and irregularly shaped blocks of cartilage in the  bronchus to keep the large airways open and so  reduce resistance to the fl ow of air. Smooth muscle  in the airways contracts and relaxes to adjust the  diameter of the airway. 4 The alveoli are lined by a squamous epithelium that  gives a short diff usion distance for the exchange  ...