Lung Disease

Lung disease – Pulmonary Tuberculosis Tuberculosis (TB) is an infectious disease that can affect any part of the body although it is usually found in the lungs. TB kills approximately 2 million people each year, more than any other infectious disease. However, TB mortality rates have fallen by over a third since 1990 and the number of TB cases has been falling since 2006.

What is the cause of pulmonary tuberculosis? pulmonary tuberculosis TB is caused by rod-shaped bacteria: Mycobacterium tuberculosis or Mycobacterium bovis. It is estimated that up to 30 per cent of the world’s population have one or the other form of the bacterium in their bodies.

What are the symptoms of pulmonary tuberculosis? Initially:  Persistent cough  Tiredness  Loss of appetite which leads to weight loss As the disease progresses:  Fever  Pallor  Night sweats  Coughing up blood  Chest pain

How is pulmonary tuberculosis transmitted between individuals in the population? There are 2 different bacteria that cause TB; Mycobacterium tuberculosis and Mycobacterium bovis. Although they are both transmitted via droplets, Mycobacterium tuberculosis is transmitted between humans while Mycobacterium bovis is transmitted from cows to humans. Pulmonary tuberculosis is highly infectious and contagious and it is spread through the air in droplets. Droplets can be released into the air when infected individuals do the following things; cough, sneeze, laugh, talk.

Mycobacterium tuberculosis is a resistant bacterium and is able to survive for several weeks once the droplets have dried. Transmission of the bacteria normally occurs following prolonged exposure to an infected person rather than a casual meeting. It is for this reason that TB usually spreads between family members, close friends and work colleagues.

Question: What conditions do you think are most likely to cause the spread of TB. Explain your answer.

TB is more likely to spread in crowded conditions because people are in closer contact with each other so itis more likely that the bacteria will be transmitted between individuals. Poor ventilation will also promote the spread of TB as this means that the infectious droplets are less likely to be removed.

Mycobacterium bovis is transmitted from cows to humans; this happens in two ways. 1) Through droplets in the air 2) In unpasteurised milk People most at risk of contracting TB are those who: Are in close contact with infective individuals. Especially if this is the case for long periods of time in overcrowded environments. Work or live in care facilities Are from communities in which TB is prevalent Have reduced immunity

Question: Give examples of groups with reduced immunity.

Very young or very old people, those with AIDS, malnourished individuals, alcoholics, injecting drug users, the homeless, people with medical conditions that make the body less able to resist disease e.g. diabetes

How does disease develop within the body? Primary infection – usually occurs in children Mycobacterium tuberculosis is inhaled and invade the epithelial cells of the upper regions of the lungs. Here the bacteria grow and divide as there is a plentiful supply of oxygen. White blood cells accumulate to ingest the bacteria The lymph nodes that drain the area become enlarged and inflamed. In healthy people, the infection can usually be controlled within a few weeks and there are few, if any, symptoms. However, some bacteria usually remain.

Post-primary infection – usually occurs in adults After a delay of months to years the remaining bacteria re-emerge and start dividing inside the lungs’ epithelial cells. The infection is not easily controlled The bacteria destroy the tissue of the lungs resulting in the formation of cavities and scar tissue. Infected individuals cough up damaged lung tissue containing bacteria and blood. The bacteria can spread through the bloodstream to other organs which can be fatal.

Lung Cavity

Prevention of TB Homework. Through carrying out your own research, prepare a poster that includes details of different ways in which TB can be prevented and controlled. You should consider the following as research points: Vaccinations Social measures Cultural measures Drug treatment You should also include a small section explaining why there has been a recent increase in cases of TB in developed countries.

Summary Questions: 1a) Which organisms can cause tuberculosis? Mycobacterium tuberculosis and Mycobacterium bovis 1b) Compare the methods of transmission for the organisms in 1a? M. tuberculosis is spread between humans in droplets when infected individuals sneeze etc. uninfected people inhale the bacterium which may then infect their lungs. M. bovis is spread between cows in droplets or in unpasteurised milk. 2) Why do you think that tuberculosis is sometimes referred to as a disease of poverty? The conditions in which TB is readily transmitted include overcrowding, poor ventialtion, poor diet and dampness are often associated with poverty. 3) Suggest why heating milk to 72°C for 15 seconds might help to control the spread of TB. M. bovis is found in cattle and their milk; it also causes TB. Heating the milk kills the bacteria so prevents the bacteria being transmitted to humans. 4) Construct a flow chart detailing the course of the TB infection Inhalation of bacterium  bacteria grow and divide in lung tissue  white blood cells ingest bacteria  inflammation and enlargement of lymoh nodes  some bacteria remain  years later bacteria re-emerge  bacteria grow and divide  lung tissue destroyed  formation of cavities  can spread to other organs via blood.

Other Lung diseases When studying lung diseases it is important to remember that the function of the lungs is to act as the interface at which gas exchange happens. In order to be efficient, the exchange surface must 1) be thin 2) have a large surface area 3) be constantly ventilated. Any factors that negatively affect any of these features will reduce the efficiency of gas exchange. We will look at the effects that 1. pulmonary fibrosis, 2.asthma and 3.emphysema have on lung function.

Pulmonary fibrosis What is fibrosis? Fibrosis is the scarring of body tissue; in this case – the lungs. The formation of scars on epithelium of the lungs results in irreversible thickening. This reduces the efficiency of gas exchange because:

In order for the diffusion of respiratory gases to occur, the epithelial cells lining the alveoli need to be thin. If there are scars and tissue is thicker, gas exchange is not as efficient because the diffusion distance is greater.

In addition to this, the scarring also reduces the elasticity of the lungs. The elasticity of the lungs aids the expulsion of air when breathing out and is due to the lungs springing back. This loss of elasticity and the increased thickness of tissues result in a reduction of the amount of air that the lungs can contain.

Honeycomb lung is a long-term consequence of pulmonary fibrosis. Areas of lung tissue are converted into multiple spaces, separated from each other by fibrous tissue.pulmonary fibrosis

How pulmonary fibrosis affects lung function and symptoms Shortness of breath, especially when exercising Considerable volume of air space in lungs occupied with fibrous tissue Less air, therefore oxygen taken in with each breath. Thickened epithelium (alveoli) = increased diffusion pathway Slow diffusion of oxygen into blood Loss of elasticity = difficult to ventilate lungs = hard to maintain diffusion gradient across exchange surface (alveoli)

Chronic, dry cough Fibrous tissue in the airways creates an obstruction Reflex reaction to remove the obstruction by coughing The tissue is immovable so nothing is expelled, the cough is dry Pain and discomfort in the chest Pressure and damage from the fibrous tissue Further damage and scarring as a result of coughing Weakness and fatigue Reduced intake of oxygen in the blood Less energy released by cellular respiration

Cause: The exact cause of pulmonary fibrosis is unclear. Evidence suggests that it is a reaction to microscopic lung injury, to which some individuals are genetically more susceptible.

Asthma

What is asthma? Asthma is an allergic response that causes difficulty breathing. It is thought to affect 10% of the world's population and is responsible for 2000 deaths per year in the UK. Asthma is not an infectious disease, but is caused by physical factors called allergens in the environment. These allergens include pollen, faeces of dust mites and animal fur. Other factors that can contribute to asthma include polluting gases like sulphur dioxide, exercise, cold weather, infection and stress.

One or more allergens causes white blood cells on the linings of the bronchi and bronchioles to release histamines. This has the following effects: Lining of airways become inflammed Cells of the epithelial lining secrete more mucus than normal Fluid leaves the capillaries and enters the airways Smooth circular muscle of the bronchioles contract, narrowing the airways - bronchoconstriction Overall, it becomes difficult to ventialte the lungs and maintain a diffusion gradient across the exchange surface as there is a greater resistance to the flow of air in and out of the alveoli.

How asthma affects lung function and symptoms Difficulty in breathing Constriction of bronchi and bronchioles Inflamed epithleial ling of bronchi and bronchioles Additional mucus and fluid in bronchi and bronchioles Wheezing sound when breathing Bronchi and bronchioles through which air passes are constricted A tight feeling in the chest Constricted bronchi and bronchioles = lungs not ventilated adequately Coughing Reflex response to clear obstructed bronchi and bronchioles.

Causes: Genetic link – runs in families Air pollution Stress Chemicals used in food and other products ‘Cleaner’ lifestyle = exposure to fewer allergens = childer more sensitve in later life

Question: An asthma attack occurs when an asthma trigger affects the bronchioles Name 2 asthma triggers Pollen, sulfur dioxide, anxiety, stress, cold air. Describe two changes that occur in an asthma attack and explain how these changes affect lung function. White blood cells release histamines which causes increased release of mucus and bronchoconstriction. The additional mucus results in difficulty in breathing. Bronchoconstriction results in difficulty in breathing, wheezing and a tight feeling in the chest.

Emphysema What is emphysema? Emphysema is caused almost exclusively by smoking and 20% of all smokers suffer from emphysema The disease develops over approximately 20 years and is virtually impossible to diagnose until the lungs have been irreversibly damaged The tar in cigarette smoke stimulates the white blood cells to release protease enzymes in the lungs. These protease enzymes (called elastase) digest the proteins forming the elastic tissue in the epithelial cells of the alveoli, so the alveoli can’t expand and recoil, making ventilation difficult. In severe cases the epithelial cells are destroyed completely, so alveoli merge to form large air sacs with a much smaller surface area. These all reduce the rate of gas exchange, so reducing cellular respiration and making any muscular activity very difficult

Chronic Obstructive Pulmonary Disease

Question: Using the information above and the images below, explain why an individual with emphysema would find it difficult to carry out strenous exercise. In the emphysematous lung tissue the surface area of the alveoli is reduced and there is a longer diffusion pathway and therefore less oxygen diffuses into the blood. As a result, there is not enough oxygen available for the increased respiration required for strenuous exercise. The elastic recoil of the lungs is reduced so breathing out is more difficult and shallower.

How emphysema affects lung function and symptoms Shortness of breath Loss of elasticity = difficult to exhale air Lungs are not emptied so it is difficult to inhale fresh air containing oxygen Smaller alveolar surface area = reduced blood oxygen levels = breath rapidly Chronic cough Body attempts to remove damaged tissue and mucus Cilia on bronchi and bronchioles destroyed so coughing increases Bluish skin coloration Poor gas diffusion in lungs = low levels of oxygen in the blood Cause and prevention: The only way to reduce the chances of getting emphysema is not to smoke at all, or to give it up. Function cannot be restored but giving up smoking can reduce the rate of further deterioration.

Summary questions: pulmonary fibrosis, asthma, emphysema Lung function Disease that interferes with function To ventilate by inhalation To ventialte by exhalation To provide a large surface area To provide a short diffusion pathway

DiseaseCauseSymptoms How Gas excahnge is slowed Risk factors AsthmaAllergens Temporary breathing difficulties, wheezing Bronchoconstricti on reduces tidal volume Pollen, dust, SO 2, cold air TB Bacterial infecction Chest pains, coughing, blood, fever, death Inflammation and scar tissue make thicker alveolar lining, reduced elasticity Overcrowding, poor diet, AIDS EmphysemaSmoking Shortness of breath, chronic coughing, blueish skin Reduced elasticity prevents exhalation, reduced surface area of alveoli Smoking Pulmonary fibrosis DustShortness of breath, chronic dry cough, pain in chest, weakness, fatigue Inflammation and scar tissue make thicker alveolar lining, reduced elasticity = difficult to ventialte lungs Coal dust, silica dust, mould spores

1. Difficulty in breathing or shortness of breath are common symptoms of lung disease. For each of the following, explain why the disease results in this symptom. Asthma Due to constriction on airways, inflamed linings and additional mucus and fluid Emphysema Due to loss of elasticity in lungs, making exhaling difficult, and a reduced surface area of the alveoli leading to patient ‘searching’ for breath Pulmonary fibrosis Due to reduced lung volume, reduced elasticity of lungs and lengthened diffusion path. 2. Link each of the following statements with one of the following diseases: fibrosis, asthma or emphysema It is caused almost entirely by smoking Emphysema Thickening of the epithelium of alveoli leads to a lengthened diffusion pathway Fibrosis It leads to a reduction in the surface area of the alveoli Emphysema It is a localised allergic reaction Asthma

Risk factors for lung disease In this section ‘lung disease’ relates to Chronic Obstructive Pulmonary Disease (COPD), which includes emphysema and chronic bronchitis. There are a variety of specific risk factors that increase the probability of someone suffering from lung disease. Smoking – 90% of sufferers are, or have been, heavy smokers Air pollution – pollutants such as SO 2 Genetic make-up Infections – people who frequently get other chest infections show a higher incidence Occupation – people working with harmful chemicals, gases and dusts.

The graph before shows that there is a correlation between smoking and premature death. However, it does not prove that smoking causes early death. There needs to be a clear causal connection between smoking and death before we can say the case is proven. To prove that smoking is the cause of early death in smokers the correct scientific process needs to be followed.

Summary questions 1. Name four risk factors associated with lung disease Smoking, air pollution, genetic make-up, occupation, infections 2. Describe in detail what the graph above is showing. 3. Using the graph above, state what percentage of non-smokers are likely to survive to age How many times greater is the likelihood of a non-smoker living to age 70 than someone who smokes over 25 cigarettes a day 5. About 10 to 15 years after giving up smoking the risk of death approaches that of non-smokers. Using this information and the pictures in the emphysema section explain to a 40-year old who smokes 30 cigarettes a day the likely impact of giving up smoking immediately.