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ocr F222 AS biology unit 4


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revision notes for unit 4, non-infectious diseases. module F222 AS biology, OCR

revision notes for unit 4, non-infectious diseases. module F222 AS biology, OCR

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  • 1. Module 4 Non-Infectious Disease 2.4.1 Non-infectious diseases are not caused by pathogens. They are not spread between people. Coronary Heart Disease (CHD) This is a type of heart disease where the problem is a restricted flow of blood to the cardiac muscle through the cardiac arteries. Remember, there are many other types of heart disease. Atherosclerosis The lining of a healthy artery is smooth, this means blood can easily flow through it. If the smooth endothelium becomes damaged (perhaps by high blood pressure), a fatty plaque or atheroma can build up in the wall, this restricts blood flow through the arteries. Phagocytic cells migrate to the damaged area and start to accumulate lipids becoming foam cells. Fatty deposits build up underneath the damaged endothelium. Smooth muscle cells in the artery lining divide to form fibrous connective tissue to repair the damage. Tissue and fatty deposits build up in the area slowly over many years. The growing plaque narrows the lumen of the artery. Eventually the plaque breaks through the endothelium which becomes roughened. A blood clot (thrombus) starts to form; this makes the lumen even narrower. If the blood clot grows too large it may block the artery or a piece of clot may break off – this is an embolus. The embolus travels in the blood until it gets to a place where the artery is too narrow for it to pass (possibly somewhere where there is already an atheroma). If the coronary artery becomes blocked in one of these ways a heart attack or myocardial infarction (MI) may occur. Coronary arteries supply heart muscle with glucose and oxygen, blockage of the coronary artery means some heart muscle may die – this is an MI. Angina When the coronary arteries become narrowed by atheroma less blood can pass through them to supply the heart muscle. Problems can occur when exercising as the heart muscle needs more glucose and oxygen for faster respiration, unfortunately, the coronary artery is too narrow to supply these. This can result in a pain called angina pectoris. 1
  • 2. What does it feel like? Pain in the centre of the chest, it feels like something is crushing the chest. Although the pain starts in the front of the chest it can spread down the left arm, towards the jaw and down towards the abdomen. Recognising a heart attack Symptoms include: • Severe chest pain – doesn’t ease with rest • Breathlessness and nausea • Feeling faint • Severe sweating • Sense of “doom” • Irregular pulse • Ashen, cold skin and blue lips. What do you do? • Make the casualty comfortable • Sit them in a supported position, knees bent • Dial 999 and ask for an ambulance, say it is a suspected heart attack. • If the person has any medication for a heart condition, they should take it. • Check / monitor the patient’s heart and breathing rate, also monitor their level of consciousness. If the patient loses consciousness be prepared to give CPR. Cardiac arrest 2
  • 3. This is when the heart no longer beats efficiently enough to pump blood around the body. MI is one of the causes of cardiac arrest. No pulse can be felt and the patient loses consciousness. The skin goes white / grey and the lips go blue. The first aid treatment is cardio-pulmonary resuscitation (CPR) Administering cardio-pulmonary resuscitation Act quickly – there are only a few minutes to act before it’s too late. Send someone else to fetch help by dialling 999 and asking for an ambulance. If the person is unconscious, check whether they are breathing, (if they are the chest will rise and fall). Check whether there is a pulse (place two fingers on one side of the persons voice box, you should be able to feel the carotid pulse). If the person has a pulse but is not breathing, check the airway is clear (remove any food from the mouth) and carry out rescue breathing (see notes from module F221). If the person is not breathing and has no pulse, they have suffered a cardiac arrest. Lay the person on their back, if possible raise the legs up 30 – 40 cm, this allows more blood to flow to the heart. Place your hand at the centre of the chest. Place the other hand on top and interlock your fingers. Keep your arms straight and fingers off the chest, press down 4 to 5 cm then release the pressure. The pressure should come from the heels of the hands. Repeat 30 times at the rate of 100 compressions per minute, then give two rescue breaths. 3
  • 4. This 30: 2 procedure needs to be repeated until help arrives. Check for any sign of breathing or pulse occasionally. If the pulse starts again continue with the rescue breathing. If breathing and pulse return move the patient into a recovery position and monitor until help arrives. The patient may be confused and anxious so try to re-assure them and keep them calm. Emergency treatment for CHD Treatment may involve use of a defibrillator. This will be done by a qualified medical practitioner of first aider. Defibrillation is when a powerful electric shock is delivered to the heart. Defibrillation use Turn defibrillator on Remove patient’s jewellery and clothing Two pads are placed on the chest, one on the upper right side and one on the lower left. The pads are plugged into the connector. The defibrillator will determine whether a shock is needed. Nobody should touch the patient. If the patient needs a shock, visual and auditory prompts are given. The operator is instructed to press a button to deliver a shock. Again nobody should touch the patient. The machine may instruct the operator to give a second shock. The operator should also check the patient’s airway is open and check for breathing and a pulse. Pulse but no breathing means rescue breaths should be given. No pulse means defibrillation should be repeated. Treatment People who have suffered an MI are usually given aspirin. Aspirin reduces the ability of platelets to cause blood clotting. Often doctors recommend MI sufferers take a low dose of aspirin each day. Surgical options Angina is often treated by angioplasty. A tiny, flexible, hollow tube (a catheter) is inserted into an artery in the arm or groin. At the tip of the catheter is a tiny balloon. The catheter is pushed along the artery until it gets to the coronary artery. The doctor can see where the catheter is because it shows up on an x-ray screen. When the catheter gets to the narrow / blocked section of the artery, the balloon is gently inflated. This squashes the fatty atheroma that has narrowed the artery and the artery is widened. Most balloons contain a stent, this is a short tube made of stainless steel mesh, this expands when the balloon is inflated and stays behind when the balloon is removed. It holds the narrowed blood vessel open. An angiogram is used to detect the blocked coronary artery using dye and an x-ray. 4
  • 5. Angioplasty: Coronary bypass surgery Used to treat blocked coronary arteries A piece of vein is taken from somewhere in the body – often the leg, this is used to bypass the blockage of the coronary artery. Single, double, triple, quadruple bypasses can occur – it depends on the number of blocked arteries. During the operation, the heart is stopped and a machine is used to pump blood around the body. Recently, some surgeons have carried out the operation without stopping the heart. Other options In a small number of cases, medication or surgery may not be effective in controlling the condition, or the heart may be too severely damaged. In this sort of case, a heart transplant may be the only option. Unfortunately, some patients may not be suitable for transplant, a donor may not be found or the patient may die while waiting for a donor. 5
  • 6. Costs of treating CHD Treating diseases of the cardiovascular system is very expensive. People are living longer and with age we are more likely to suffer from CHD, strokes etc.. NICE (National Institute for Health and Clinical Excellence), an independent organisation, is responsible for providing national guidance on promoting good health and preventing and treating ill health. NICE produces guidance in three areas of health: • Public health – guidance on the promotion of good health and the prevention of ill health for those working in the NHS, local authorities and the wider public and voluntary sector. • Health technologies – guidance on the use of new and existing medicines, treatments and procedures within the NHS. • Clinical practice – guidance on the appropriate treatment and care of people with specific diseases and conditions within the NHS. NICE guidance is issued so that all health professionals can benefit from the latest research and best practice can be used in treating all patients. NICE aims to make treatment as cost-effective as possible. Global distribution of CHD Epidemiologists study the global patterns of CHD, by analysing data from individual populations’ factors that pre-dispose people to develop CHD can be established – these are called the “risk factors” Risk factors Diet – high salt diets increase the risk of CHD, this is because salt increases blood pressure. High levels of saturated fat in the diet increase blood cholesterol levels, this also increases the risk of CHD. Anti- oxidants are found in some foods, they reduce the risk of developing CHD, for example, vitamin C, found in many fresh fruits and vegetables is most beneficial. Blood pressure – high blood pressure can cause damage to the endothelium in the arteries, this increases the chances of atheroma developing. Exercise – exercise (aerobic) lowers blood pressure and blood cholesterol, which helps prevent CHD. Physical activity also reduces the chances of developing obesity, (another risk factor). Smoking – the greatest risk factor. Smoking raises blood pressure, increases the development of atheroma and increases the chances of a blood clot forming. Genetic influences – some people have genes which predispose them to higher blood pressure and high blood cholesterol levels. Men are more at risk than women up to the age of menopause. After this the risk is the same. Some races have a higher rate of CHD too. For example, in the UK Afro- Caribbean’s have a higher rate of CHD than others, it is not clear whether this is due to genes or other social or economic factors, e.g. diet. 6
  • 7. Body mass index Being overweight is a risk factor for CHD, also for developing type II diabetes. There are two methods of assessing whether a person is overweight. 1. Calculating BMI 2. Waist-to-hip ratio Body Mass Index The relationship between weight and height is calculated by: Weight (kg) divided by height (m) squared. Ideal range – 20 to 24.9 BMI over 25 or higher – person is considered overweight. BMI over 30 – person is considered obese Waist-to-hip ratio The way that fat is distributed around the body is important. People with a lot of fat around the abdomen are most at risk. These people are said to have “central adiposity” and are classed as apple shaped. To determine whether you have central adiposity, measure around the waist in centimetres. A healthy man should have a waist circumference measurement of less than 94 cm; a healthy woman should have a waist circumference of less than 80 cm. Alternatively, establish the waist-to-hip ratio. Measure the waist at the height of the umbilicus (navel) and the hips around the widest point. Divide the waist measurement by the hip measurement. In men the ratio should be less than 1.0; in women the ratio should be 0.8 or less. Lung disease Some lung disease is described as acute – they only happen for a short time and then the person gets better, e.g. acute bronchitis, an infection of the lungs caused by a virus. Some lung disease is described as chronic, chronic diseases start slowly but last for a long time, they are rarely cured. An example is chronic bronchitis, caused by smoking. Smoking and its effects on the respiratory system Tobacco smoke contains many different chemicals. The main ones harmful to health are carbon monoxide, nicotine and tar. Carbon monoxide is a gas that diffuses through the walls of the alveoli into the blood. It combines with haemoglobin in the red cells to form carboxyhaemoglobin. This remains combined with the carbon monoxide making it unable to carry oxygen. The problem is that haemoglobin will combine with carbon monoxide more readily than it combines with oxygen so even a small amount of carbon monoxide will significantly reduce the amount of oxygen that a person’s blood will carry. A smoker’s blood may carry up to 15% less oxygen than a non-smoker’s – this is why so many smokers suffer from 7
  • 8. breathlessness especially when they exercise. Carbon monoxide also increases the heart rate, as the heart has to pump more often to get the same amount of oxygen to body tissues. Tar – a large proportion of the tar in tobacco smoke ends up deposited in the bronchi, bronchioles and alveoli. The epithelium becomes irritated causing inflammation. The cilia on the ciliated epithelium cells becomes paralysed, this means it can no longer move mucus back upwards towards the throat. Therefore, mucus containing dirt and micro-organisms builds up in the lungs. Tar also stimulates mucus production by the goblet cells. A smoker becomes more prone to lung infections as micro- organisms are not removed from the respiratory system. A persistent cough develops as the body tries to get rid of the accumulated mucus. The mucus also has a number of effects on gas exchange in the lungs. • Mucus reduces the diameter of the bronchi and bronchioles, reducing the rate at which air can reach the alveoli. • Coughing can damage the bronchi, bronchioles and alveoli. Scar tissue is produced; this lowers the rate of diffusion and narrows the diameter of the airways. • Mucus builds up in the alveoli, reducing the volume of air that they can hold and increasing the diffusion pathway. • Infections in the lungs lead to the development of emphysema (the walls of the alveoli break down). This reduces the surface area available for diffusion. • The mucus building up in the lungs also contains allergens such as pollen. This causes inflammation of the bronchi and bronchioles; the rate at which air can enter the alveoli is reduced. It can also lead to asthma attacks. Chronic bronchitis The build up of mucus in the lungs and the effects as listed above, lead to a condition called chronic bronchitis. This condition develops slowly. The main symptoms include breathlessness and a persistent cough. Once established, it is very difficult to improve the symptoms. Emphysema In a healthy person white blood cells produce an enzyme called elastase; this helps them to digest tissues to reach the site of an infection. In smokers, the presence of irritants in the mucus that build up in the lungs causes inflammation. This causes large numbers of phagocytic white blood cells to be attracted to the alveoli. The elastase produced by the cells breaks down elastin and some other proteins in the walls of the alveoli. In healthy people there is an inhibitor to stop tissue damage by elastase; unfortunately, in smokers the inhibitor is inactivated. As the elastin and other proteins break down, the alveoli become enlarged and damaged. The surface area available for gas exchange is reduced. The reduced surface area causes breathlessness in the smoker. They breathe in more deeply; the remaining elastin becomes stretched – permanently. In a healthy person, elastic recoil from these elastin fibres helps to force air out of the alveoli when breathing out. In a person with emphysema, some stale air remains in the alveoli, this makes gas exchange even less efficient. 8
  • 9. As emphysema worsens, the person becomes increasingly disabled. This can means some people cannot even get out of bed. The person can be given oxygen from a cylinder to breathe in. The damage is irreversible. Death from respiratory failure usually results. Chronic obstructive lung disease (COPD) Chronic bronchitis and emphysema are both caused by smoking – the two conditions usually occur together. People with these conditions are said to have chronic obstructive lung disease (COPD). Lung cancer Tobacco smoke contains a number of carcinogens (chemicals that cause cancer). Theses carcinogens cause mutations in the genes of epithelial cells that line the lungs. Some genes control cell division, if these genes mutate uncontrolled cell division can take place. p53 is a tumour suppressor gene. Benzopyrene, the chemical found in the tar from cigarette smoke, binds to p53 and inactivates it. The epithelial cells divide uncontrollably leading to formation of a tumour. Symptoms of lung cancer: • Breathlessness, due to the tumour blocking the airways and damaging the alveoli • Wheezing caused by air being forced down obstructed airways • A persistent cough, resulting from the tumour obstructing the airways • Sputum stained with blood due to the tumour causing damage to the lung tissue • Changes in the voice may occur if the tumour presses on the airways of the larynx (voice box). Asthma This is a disease that affects the trachea, bronchi and bronchioles of the lungs. It is sometimes referred to as reversible obstructive airway disease or ROAD. Asthma does not affect sufferers all of the time. There may be a genetic link to its development, however, why some people develop asthma and other do not, is still not fully understood. During an asthma attack, membranes lining the airways release mucus and become inflamed. The inflammation causes the muscles of the airways to contract, the airways narrow. This is called bronchoconstriction. Mucus also blocks the airways, this leads to wheezing, which is the sound heard as the airways constrict and make it difficult for air to escape. 90% of all asthma is allergic asthma; the asthma is triggered by allergens – substances capable of causing an allergic reaction. Example of allergens include: fur from household pets; pollen; dust mites and their faeces; mould spores; pollutants; smoke and many chemicals. An allergic reaction happens when the immune system over-reacts to something in the environment. This kind of asthma mostly develops in younger people, before the age of 40. Most childhood asthma is related to allergy. One cause may be due to a mother smoking during pregnancy, or parent smoking in the home. The 9
  • 10. cigarette smokes irritates the respiratory tract of children and increases the chances they will develop allergic asthma. Intrinsic asthma – typically develops after the age of 40, allergies play no part in it. It can be caused by respiratory irritants such as perfumes, cleaning agents, fumes, smoke or infections of the upper respiratory tract. This type of asthma is harder to treat than allergic asthma. Exercise-induced asthma – can affect anyone at any age. Usually caused by the loss of heat and moisture from the lungs this happens during strenuous exercise. The symptoms are worse during cold, dry weather. Nocturnal asthma (sleep related asthma) – may be triggered by allergens in the bedding or bedroom, or a decrease in room temperature. It is estimated that 75% of asthmatics suffer from nocturnal asthma Occupational asthma – develops as a result of breathing chemical fumes, wood dust or other irritants over a long period of time. Treatment for asthma Steroids – treatment uses a group of steroids called corticosteroids; these are usually taken with an inhaler, twice a day. By inhaling them the drug is delivered straight to the lungs and causes fewer side effects. Steroids may also be given in tablet form, syrup form or via an injection if the asthma is severe. Steroids work by reducing the inflammation in the airways; they work slowly but have a long-term effect in reducing the severity of asthma attacks. They can be used when a person is having as asthma attack. Beta-agonists – also used to treat asthma. They act as bronchodilators, relaxing the muscles that constrict the airways. They are inhaled, so are delivered straight to the place where they are needed. They may also be taken in tablet or syrup form. In the case of a very severe asthma attack, a person may need to attend hospital. Steroids will be given; they may be injected into the blood. Beta-agonists will also be given to relax the muscles, and the person may be given oxygen to help with breathing. Diabetes 10
  • 11. In normal sugar metabolism the concentration of glucose is monitored by cells in the pancreas. If the glucose concentration becomes too high, the beta cells of the pancreas secrete insulin. This stimulates cells to take up glucose and respire it and muscle and liver cells to take it up and convert it into glycogen for storage. When blood glucose levels fall, insulin secretion stops and the hormone glucagon is secreted by the alpha cells of the pancreas. This stimulates the breakdown of glycogen to glucose and glucose is released into the bloodstream/ Type I diabetes Usually diagnosed in children and young adults. Occurs because the immune system has attacked the insulin producing cells in the pancreas. The pancreas produces little or no insulin. As insulin is the hormone that regulates blood glucose concentration, in a person with type I diabetes, the blood glucose level can become too high or too low. If left untreated the person may go into unconsciousness or coma. This kind of diabetes is treated with regular insulin injections. It is not known what causes type I diabetes although both genetic and environmental factors are involved. Type II diabetes Usually develops in adults over the age of 40, there are concerns that some children are developing this kind of diabetes, there are strong links to the increases in childhood obesity. This is the commonest form of diabetes. People may not be producing enough insulin; they are also insensitive to the insulin produced. People who have diets high in sugars are most likely to develop insensitivity, there are other cases too. This kind of diabetes is not usually treated using insulin as the body does not respond properly to this. Therefore, this form of diabetes is controlled by exercise and diet. The advice is to eat more complex carbohydrates (starch) as they are digested slowly into glucose, hence avoiding rapid rises in blood glucose. They are also advised to eat less sugar and salt and more fruit and vegetables. Factors triggering type II diabetes: • Old age • Obesity • High blood pressure • Physical inactivity • Family history of diabetes Experts estimate there could be hundreds of children with type II diabetes in the UK. Most of these cases are amongst the Asian population. This is due to a combination of genetic factors, diet and lack of exercise. Research indicates the white population is also at risk. Clearer food labelling, schools stopping junk food etc are all initiatives aimed at reducing the risks of developing this type of diabetes in children 11
  • 12. Health risks associated with diabetes Uncontrolled diabetes leads to high blood glucose levels. Over time this can cause damage to nerve cells; damage to the retina of the eye that can lead to blindness; kidney failure; high blood pressure; heart disease; strokes; chronic infections; wounds that will not heal and other conditions. Measuring blood glucose levels A person with diabetes should try to keep their blood glucose concentration at a safe level. Healthy blood glucose levels stay within narrow limits throughout the day: 4 – 8 mmol dm -3. Blood glucose levels are higher after meals and usually lowest in the morning. A person with diabetes should aim for the following limits: • 4 – 7 mmol dm-3 before meals • Less than 10 mmol dm-3 90 minutes after a meal • Around 8 mmol dm– 3 at bedtime. A person with diabetes can use a biosensor to measure blood glucose levels. This contains a strip with enzymes (glucose oxidase), on it. This converts any glucose in the blood to gluconolactone. As it does this a small electric current is produced. This is detected by an electrode on the test strip and a reading for blood glucose concentration is produced on a digital display screen. Using a biosensor 1. Place a test strip in the glucose test meter 2. Disinfect the skin with alcohol 3. Use a sterile lancet inside a device that looks like a pen to prick the skin 4. The small drop of blood produced should be squeezed onto the test strip. 5. After approx 30 seconds a reading for the blood glucose concentration will appear on the digital display screen. 6. The glucose test meter has a memory so that measurements can be stored providing a record of changes in blood glucose. Diagnosing diabetes The fasting blood glucose test 12
  • 13. The person being tested eats and drinks nothing (except water) for 8 to 12 hours before taking the test. A blood sample is then taken Blood glucose level mmol dm-3 Interpretation 3.6 – 6.0 Normal glucose tolerance 6.1 – 6.9 impaired glucose tolerance 7.0 and above probable diabetes Glucose tolerance test The most common glucose tolerance test is the oral glucose tolerance test (OGTT). The patient eats normally for several days up to the test, but does not eat or drink anything after midnight on the evening before the test. When the person arrives for the test a blood sample is taken. The person is then asked to drink a liquid containing a measured amount of glucose (usually 75g). More blood samples will be taken every 30 minutes until 3 hours have passed. Interpretation is as follows: Blood glucose level 2 hours after 75g glucose Interpretation drink / mmol dm-3 less than 7.8 Normal glucose tolerance 7.8 – 11.0 impaired glucose tolerance more than 11.1 probable diabetes It is important to remember that a high glucose level might indicate another medical condition; some drugs the patient may be taking might also interfere with the results. A doctor may probably investigate further before diagnosing diabetes mellitus The growing problem of diabetes The number of cases of diabetes has increased in many countries. The increase is blamed on growing wealth – this means there is plenty of food available, particularly refined, processed foods. There also more cars, hence people take less exercise. 13