Chapter 12.pdf

Chapter 12 Social and preventative medicine By the end o this chapter you should be able to: a

discuss the causative relationships among diet, obesity and diabetes;

b

describe the eects o ats on the cardiovascular cardiova scular system, including reerence to plaque ormation, atherosclerosis, coronary heart disease, hypertension and strok stroke; e;

c

investigate the immediate eects o exercise on investigate the body;

d

discuss the consequences o exercise on the body and the benets o maintaining a physically t body, with reerence to the prevention o chronic diseases, VO VO2 max and cardiac eciency;

describe the mechanisms o inection or AIDS and dengue ever and their causativ cau sativee agents, including the process o inection and the replication o the disease-causing organisms;

 

explain how AIDS and dengue ever are transmitted;

g

assess the impacts o AIDS and dengue ever regionally,, including reerence to social and regionally economic issues;

h

discuss the roles o social, economic and biological actors in the prevention and control o AIDS and dengue ever.

Diet and health

Obesity

What a person eats, and how much they eat, can have ha ve a very large eect on their health. Eating a balanced diet is a good way to increase the chance o ha having ving a long and healthy lie. lie. A balanced diet can be dened as a diet containing all o the dierent nutrients required by the body, and that supplies the appropriate amount o energy. Table 12.1 lists the main nutrients that should be present in the diet, and describes how these nutrients are used in the body.

We have already seen how eating too much and exercising too little can cause a person to become seriously overweight, and that this greatl greatly y increases the risk o developing Type Type 2 diabetes (page 187). A person who is very overweight is said to be obese. Obesity is sometimes dened as having a body mass index (BMI) greater than 27. The ormula or calculating BMI is:

SAQ 

Obesity results rom consistently eating nutrients that contain more energy than the body uses. The ‘spare’ energy energy is stored in the orm o at, which builds up as adipose tissue underneath the skin and around the body organs. organs. Obesity seriously increases the risk o developing not only Type 2 diabetes, diabetes, but also heart disease and arthritis (Figure 12.1 and Figure 12.2).

1 a Which o the nutrients listed in Table Table 12.1 are organic chemicals? Table 12.1 can b Which o the nutrients listed in Table be used by the body in respiration, to release energy and make ATP?

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e

weight in kilograms (height in metres)2

Chapter 12: Social and preventative medicine

Nutrient

Function

Good ood sources

Notes

carboh car bohyd ydra rates tes

providi prov iding ng ener energy gy,, whic which h is released by respiration inside body cells

bread, rice, potatoes, pulses (beans, lentils and peas), breakast cereals

carbohydrates include sugars carbohydrates and starches; starches are better than sugars because they take longer to digest and the energy in them is released more steadily

proteins

ormation o ne new cells and tissues, and o many important substances, including haemoglobin, collagen and enzymes; can be respired to provide energy

meat, eggs, sh, dairy products, pulses

proteins contain 20 dierent amino acids, o which 8 are essential in the diet as the body cannot make them rom other amino acids

lipids

making cell membranes, and steroid hormones; provi providing ding energy when broken down in respiration–ats provide twice as much energy per gram as carbohydrates or proteins

dairy products, red meat, oily sh, plant oils

lipids contain several dierent atty acids, acids, o which two are essential in the diet; oods containing lipids are also important sources o at-soluble vitamins

vitamin A (at soluble)

making the pigment rhodopsin, ound in the rod cells in the eye and essential or vision

meat, egg yolks, carrots

daily doses at around 100 times the recommended daily intake are toxic

vitamin C (water soluble)

making collagen

citrus ruits, blackcurrants, potatoes

vitamin D (at soluble)

or orma mati tion on o bone boness and and te teet eth h

dairy dair y oo oods ds,, oi oilly sh, egg yolks

this vitamin is also made in the skin when exposed to sunlight

iron

ormation o haemoglobin

meat, beans, chocolate, shellsh, eggs

shortage o iron in the diet is a common cause o anaemia

calcium

bone ormation and blood clotting

dairy products, sh

lack o calcium in the diet can increase the risk o osteoporosis

Table 12.1

Nutrients and their roles in the body.

The incidence o obesity has been steadily increasing. Most people have easy access to as much ood as they want, and much o this ood is very ‘energy-dense’–it contains a lot o kilojoules per gram. This is oten true o ast ood, such as burgers and ries. On the other side o the coin, many people do not use up a great deal o energy each day; we have become much more sedentary, spending more time sitting and relaxing rather than walking or playing sport. The combination o  eating more and exercising less is building up what

Figure 12.1

A normal mouse and an obese mouse.

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many nutritionists are calling the ‘obesity time bomb’. The increasing number o people who are obese now will result in an increasing number o  people with obesity-related diseases in the uture.

Diet, obesity and diabetes

Figure 12.2 Obesity is most damaging when at accumulates around the abdomen. It greatly increases the risk o developing Type Type 2 diabetes.

In Chapter 10, we saw that there are many dierent risk actors or Type 2 diabetes. The prevalence o diabetes in the Caribbean is increasing, and–as people’ss genes are not changing–it appears that people’ this is due to changes in liestyle. Obesity is a major risk actor or diabetes (page 187). Some research suggests that, at least in the West, around 90% o cases o Type 2 diabetes are caused by being overweight. Worryingly, more and more children are becoming obese, and this is believed to be greatly increasing the numbers o people who are likely to develop diabetes as they get older. Figure 12.3 shows the change in the percentages o young people who are obese in the USA, and a similar situation exists in the Caribbean.

What causes obesity? There’s no doubt that some people have a much greater tendency to put on weight than others. While quite a bit o this can be put down to environment and liestyle–including the diet eaten, amount o exercise taken and straightorward willpower–scientists have long believed that there is also a strong genetic infuence on our likelihood o becoming obese. For example, studies o identical twins show that they have have a very high resemblance in their tendency to become obese, even i they are brought up in completely dierent envir environments onments.. It seems likely that genetic infuences on obesity are polygenic–that is, there are many dierent genes that each ha have ve a small eect. There are just a ew examples o a single gene that can have a large eect, but they are very rare. For example, a two-year-old boy who weighed almost 30 kg was ound to have a mutation in a gene that normally codes or a

protein called leptin, which has been linked to the control o appetite. The discovery o leptin was rst made in mice, in 1994. Various strains o mice are kept and bred in laboratories, laboratories, and one o these strains is extremely obese (Figure 12.1). The obese mice were ound to have a single gene mutation that prevented them rom making leptin. Leptin is made in at storage cells, in adipose tissue. The more at there is, the more leptin is made. Leptin travels in the blood to all parts o the body, where it has several dierent target organs. Among these is the brain–leptin provides an ‘I am ull’ signal to the brain, suppressing appetite. As at stores dwindle, less leptin is produced and the mouse eels hungrier. The obese mice ha h ave no leptin, so their brains never get a ‘ull’ signal, and they always eel hungry. There were high hopes that this discovery might help to explain obesity in humans. continued ...

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We also produce leptin, and it was thought that perhaps giving people leptin might suppress their appetites and help them to lose weight. But results o trials have not been encouraging. Leptin may play a role in our desire to eat, but it isn’t a magic bullet that can reduce obesity. Indeed, many obese people already have high levels o leptin in their blood, and it seems that the problem is more in the way the brain responds to it than the actual production o  leptin by the at cells. Various other studies have ound potential candidate genes that might aect the tendency to put on weight. One o the best studies was reported in 2007. A group o researchers in Europe had been looking or a genetic link to the tendency to develop Type 2 diabetes. They had screened 2000 people with Type 2 diabetes, and ound a strong correlation with the presence o a particular allele called FTO. The link was so strong that the team decided to expand their study, and to look not only at diabetes but also

obesity. They used a huge sample o 38 759 obesity. people, rom Britain, Italy and Finland. They ound that people who were heterozygous or this allele were, on average, 1.2 kg heavier than people who did not have it. People who were homozygous or the allele were, on average, 3 kg heavier. heavier. Around 50 % o people were heterozygous and 16 % homozygous. It looks as though this research has identied one o the many genes that are proba probably bly involved involved in determining the likelihood o becoming obese. There must be many more yet to be discovered. But we cannot put all the blame on genes. There is no suggestion that our genes have changed in the last 50 years, but there is no doubt d oubt that the proportion o obese people has increased greatly. greatly. This can only be down to liestyle. Some o us may nd it more dicult than others to keep our weight down, but we can still take care over diet and exercise and try to maintain weight at a healthy level.

20 Age group 2–5 year-olds 15

6–11 year-olds

   %    /   e    t   a   r 10   y    t    i   s   e    b    O

12–19 year-olds

5

0 1971–1974

Figure 12.3

1976–1980

1988–1994

2003–2006

Change in percentages o young people who are obese (data rom the USA).

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Symptoms o diabetes Studies in the Caribbean indicate that at least 50% o people with diabetes do not know that they have it. Every second person who is diagnosed with diabetes already has developed some complications, as a result o having the disease or some time but not being treated or it. There is no doubt that diagnosing the disease early allows the person to manage their diabetes successully, and helps them to maintain a much higher level o health. Many people have Type 2 diabetes or years without knowing it. First symptoms can go unrecognised. The person may eel tired or thirsty all the time, but as the development o these symptoms is slow they may just creep up stealthily and be unnoticed. An understanding o what is going wrong can explain these symptoms symptoms.. Imagine that a diabetic person eats a meal containing a lot o sugar. As this is absorbed, blood glucose levels go well abo above ve normal, but the liver and muscle cells are not alerted and do not n ot take corrective action. The very high blood glucose levels mean that the kidneys (Chapter 8) are not able to stop glucose being excreted in the urine. Instead o  being stored in the liver as glycogen, much o  the glucose is lost rom the body. Later, when the glucose in the blood has been used in respiration, and i the person does not eat again, blood glucose levels may drop well below normal. The liver cells have ha ve not stored any as glycogen, so they cannot release glucose to bring up the level in the blood. The person eels very tired and may even become unconscious. Having Ha ving a high blood glucose level is known as hyperglycaemia. It is usually dened as a level above abo ve about 250 mg per 100 cm3 (15 mmol dm−3). In the short term, hyperglycaemia makes the person eel unwell. They may have a dry mouth and blurred vision. They may also eel very thirsty, because the high concentration o glucose in the body fuids reduces their water potential; this is detected by the hypothalam hypothalamus, us, which sends nerve impulses to parts o the brain that control eelings o thirst. The person may be conused. Sometimes hyperglycaemia is associated with ketoacidosis, caused by the presence o substances called 248

ketone bodies in the blood. The ketone bodies are produced rom atty acids in the liver, and can be used as respiratory substrates. However, in diabetes they may be produced aster than they are used and high concentrations o them can be dangerous. Up to 10% o diabetic people admitted to hospital with ketoacidosis die. Having Ha ving a low blood glucose level is known as hypoglycaemia. The person eels exceptionally tired and may become conused and show irrational behaviour. Hypoglycaemia is not restricted to people with diabetes. Many Many normal people can become mildly hypoglycaemic hypoglycaemic i they have not eaten or a while, and be quite unaware that their mood and behavi behaviour our have changed as a result. However, a person with diabetes is more likely to suer severe attacks o hypoglycaemia. I caught early, hypoglycaemia is easily treated by eating something sugary.

Treating diabetes As yet, there is no cure or diabetes. The management o diabetes mellitus revolves revolves around keeping blood glucose concentrations reasonably reasonably constant. The patient may need to check their blood glucose regularly regularly,, which is generally done with a simple sensor providing a digital readout (Figure 12.4). Urine can also be checked or glucose, glucose, using a dipstick, or example (Figure 12.5). I the illness is under control, then there should be no more than very small amounts o glucose present in urine. In Type 2 diabetes, a well-controlled diet may

Figure 12.4 Measuring blood glucose concentration.

Chapter 12: Social and preventative medicine

SAQ 

3 The graph shows the changes in blood glucose concentration in a person who ate 50 g o  carbohydrate carbohy drate as wholemeal bread, and others who ate 50 g o carbohy carbohydrate drate as lentils and as soya beans.

Figure 12.5 urine.

Measuring glucose concentration in

be able to keep symptoms at bay. I the patient is obese, then weight loss through diet and exercise will be the rst target. It is oten possible to manage Type 2 diabetes, at least in the early stages,, through diet alone. The person needs to stages eat small meals at reasonably regular intervals, never fooding their blood with excess glucose and never allowing blood glucose levels to drop too low. Polysaccharides are a better carbohydrate source than sugars, because it takes time or them to be digested and then absorbed, spreading out the time over which sugars are absorbed into the blood and avoiding a sharp ‘spike’ in blood glucose concentration. SAQ 

2 Suggest why testing the concentration o  glucose in blood is more useul than testing the concentration o glucose in urine.

a Explain the shape o the curve when bread was eaten. b Describe the dierences between this curve and the ones showing the results ater lentils and soya beans were eaten. c Suggest reasons or these dierences.

Diet and heart disease I you live to be 80 years old, your heart will beat at least 2.5 billion times. Your lungs will infate and defate at least 600 million times. Inevitably the body systems become less ecient as we get older, older, but there is a great deal that we can do to help to keep both the cardiovascular system and the gaseous exchange system working strongly, even as we age. Coronary heart disease, oten abbreviated to CHD, is a common disorder o the blood vessels that supply the heart muscle with oxygenated oxygenated blood. It is the leading cause o death in the Caribbean (Figure 12.6). The ability o the cardiac muscle to contract depends on it receiving a continuous supply o 

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120   r   e   p   s    h    t   a   e    d  n   o    f   i   o   t    l   r   a   e  u    b  p   o   m  p   u   0   n    /   0    0   e   0    t   a   r   0    1   y    t    i    l   a    t   r   o    M

heart disease cancers 80 cerebrovascular cerebrovascul ar disease (stroke) diabetes mellitus

HIV / AIDS accidents acute respiratory inection

0 1985

Figure 12.6

illness resulting rom high blood pressure

40

1990

1995

The eight leading causes o death in the Caribbean between 1985 and 2000.

oxygen. The muscle uses the oxygen or aerobic respiration, respirati on, which provides the energy that it uses or contraction. I the oxygen supply ails, ails, then the muscle cannot contract. Heart muscle lacking oxygen quickly dies. CHD is caused by atherosclerosis in the coronary arteries (page 110). Atheroscler Atherosclerosis osis is sometimes known as ‘hardening o the arteries’. Atherosclerosis Atheroscler osis can lead to the coronary arteries becoming blocked. Usually, Usually, the blockage is due to the build-up o material inside the artery walls, which makes the space through which blood can fow–the lumen–much narrower. Atherosclerosis SAQ 

4 These questions are about the data in Figure 12.6. a What was the major cause o death in the Caribbean countries in each o the years shown in the graph? b Describe the changes in mortality due to diabetes between 1985 and 2000, and suggest reasons or these changes. c Describe the changes in mortality due to HIV/AIDS between 1985 and 2000, and suggest reasons or these changes ch anges..

250

2000

can also occur in other arteries, including those supplying the brain. Atherosclerosis develops slowly, and people do not normally show any symptoms until they are at least 40 years old. It occurs naturally as part o the ageing process. However However,, in some people it progresses progr esses more rapidly and this can be due to a variety o actors that tend to damage the lining o arteries arteries.. These include high blood pressure, pressure, the presence o harmul chemicals such as those in tobacco smoke, or low-density lipoproteins (LDLs, described on pages 252–253). The damage damage,, and the attempts by the body to repair itsel, build up tissue and chemicals in the artery wall. These deposits are known as an atheromatous plaque (Figure 12.7). Once the plaque has reduced the lumen o a coronary artery by 50% or more, the fow o blood through the artery cannot keep up with the oxygen requirements o the heart muscle during exercise. The person experiences pain when exercising, known as angina. The pain is oten in the let shoulder,, chest and arm, but or some people also shoulder in the neck or the let side o the ace. Blood clots can orm on and around the plaque. Such a blood clot is called a coronary thrombosis. This happens because platelets in the blood come

Chapter 12: Social and preventative medicine

blood in lumen protective inner  lining o the artery

artery wall

atheromatous plaque

a plaque is rigid normal artery wall is elastic

blood clots

damage to wall 1 Part o the lining o the artery is damaged.

Figure 12.7

2 Gradually, over time, cells divide in the artery wall and there is a build-up o lipids.

3 Exercise or stress can make the plaque break. Blood enters the crack. Platelets in the blood are activated and a clot orms. Part o the clot may break o.

The development o an atheromatous atheromatous plaque.

into contact with collagen in the artery wall. The platelets then secrete chemicals that stimulate the blood to orm a clot. The blood clot narrow narrowss the artery even more. It may break o and get stuck in a smaller vessel. The part o the heart that is supplied by this blood vessel stops beating, and some o the muscle cells may die. This is known as a myocardial inarction and is an extremely dangerous dangerous condition.

Myocardial inarction ‘Myo’ means ‘muscle’, and the myocardium is the muscular wall o the heart. ‘Inarction’ is a term describing the loss o sucient blood fow to a tissue to allow it carry out its normal activity activity.. Around 90% o instances o myocardial inarction are caused by a coronary thrombosis. thrombosis. I the inarction involves a large amount o  muscle, the person may die almost immediately. Severe myocardial myocardial inarction may cause the heart to stop beating. This is called cardiac arrest (heart attack) (Figure 12.8). No pulse can be elt, and the victim rapidly loses consciousness consciousness.. Others may not lose consciousness, but experience such severe pain that they call or help

straight away. I less muscle is aected, the pain may be less severe, and the patient may wait several hours beore calling a doctor. Sometimes, Sometimes, they may not even realise that they ha have ve had a minor inarction, and do nothing. The pain is usually elt near the centre o the thorax, behind the sternum, and is described as ‘crushing’ or ‘bursting’.

Figure 12.8 A paramedic applying chest compressions to get the heart to beat again ater cardiac arrest.

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The commonest time o day or acute myocardial my ocardial inarction is rst thing in the morning, when the patient has just got up. There is another peak around 5 p.m. Friday is the commonest day o the week or a myocardial inarction, inarction, and there are ewer at weekends. No-one really understands the reasons or these patterns patterns,, but it is thought that stress or excitement may be involved, causing a rise in blood pressure, which may may rupture a plaque in a coronary artery.

Diet and coronary heart disease It seems that every week there is some new advice about what what we should and should not do to maintain a healthy heart. For example, in the 1950s, people were told to drink milk and eat eggs to stay healthy. Then the health experts decided that these, and many other ‘atty’ oods, were bad or us. Why so much conusion? The diculty is that we cannot quickly and easily do properly controlled experiments into the eect on human health o a particular actor in the diet. There are too many variables involved that we cannot control. In particular, it seems that small dierences in our genes make us respond to a particular type o diet in dierent ways. ways. However Howev er,, there is a great deal o evidence that shows that having having a high level o cholesterol in the blood does increase the risk o suering rom CHD.. What is less clear is the extent to which diet CHD aects blood cholesterol levels. levels. There is evidence that eating a diet high in saturated ats can increase your blood cholesterol level and thereor thereoree your risk. However, other investigations have ailed to nd hard evidence that makes a direct link between the amount o cholesterol that you you eat and your risk o heart disease. It appears that eating a lot o  saturated satura ted ats is more harmul than eating a lot o  cholesterol. HDLs and LDLs The structures, properties properties and unctions o ats (lipids) and cholesterol were described in Unit 1, Chapter 1. Cholesterol is an important constituent o cell membranes. I we do not take in enough in our diet, then the liver makes cholesterol that that can be transported around the body and used by cells. 252

protein phospholipid

cholesterol

other lipids (triglycerides and steroids) 10 nm

Figure 12.9

Lipoproteins.

Cholesterol is not soluble in water, and so it cannot be transported in solution in the blood plasma. It is carried in the blood plasma in the orm o  lipoproteins –tin  –tiny y balls made up o various lipids, cholesterol and proteins (Figure 12.9). Lipoproteins come in several varieties, varieties, with dierent proportions o protein molecules and lipid molecules, including cholesterol. ch olesterol. Proteins tend to be denser than lipids, so the more protein there is, the greater the density o the lipoprotein. The lipoproteins are named according to their densities (Table 12.2). HDLs usually pick up cholesterol rom body cells that are dying, or whose membranes are being restructured, and transport it to the liver liver.. LDLs usually carry lipids and cholesterol rom the liver to other parts o the body. body. Chylomicrons are ormed in the wall o the ileum rom ats which High-density lipoproteins–HDLs

a lot o protein and relatively small amounts o lipids

Low-density lipoproteins–LDLs

more lipid and less protein than HDLs

Chylomicrons

contain a lot o lipid and very little protein

Table 12.2

Types o lipoproteins lipoproteins..

Chapter 12: Social and preventative medicine

have been digested and absorbed. They transport have lipids rom the small intestine to the liver liver..

Cholesterol and CHD LDLs have have a tendency to deposit the cholesterol that they carry in the damaged d amaged walls o arteries arteries.. This cholesterol makes up a large proportion o  an atheromatous plaque (Figure 12.7). There is a positive link between the level o LDLs in the blood and the risk o suering rom CHD and possibly a heart attack. HDLs, on the other hand, seem actually to protect against CHD. They remove cholesterol rom tissues, tissues, including the tissues in the walls o  blood vessels. In the past, health proessionals were simply simply concerned about the quantity o cholesterol in the blood. Now attention has shited to the relative proportions o ‘good’ HDLs and ‘bad’ LDLs. LDLs. The higher the proportion o HDLs, the lower the risk o heart disease. So how can someone increase their proportion o HDLs? Diet does have an eect in some people. A diet that is very rich in saturated ats (ats rom animal-derived oods) may result in a high LDL concentration. A person who eats that sort o  diet may benet rom switching to one that is low in saturated ats. This would probably involve reducing the amounts o meat and dairy products in the diet, and increasing the amounts o plantderived oods and sh. Almost all studies show a link between eating sh and protection against CHD.

Blood pressure, hypertension and stroke Blood pressure is the pressure exerted by the blood on the walls o the blood vessels through which it fows. Although most scientists now use the internationally recognised units or pressure–  either Pa (pascals) or N m−2 (newtons per square metre)–the medical proession still tends to use the old units o mm Hg (millimetres o mercury). This is because the old styles o instruments used the height to which a column o mercury was raised as the method o measuring blood pressure (Figure 12.10).

Figure 12.10 Measuring blood pressure using a sphygmomanometer.

When your blood pressure is measured, two numbers will be recorded. The rst is the systolic blood pressure. This is the maximum pressure in the artery (usually the brachial artery in the arm), resulting rom the orce produced when the ventricles contract. The second number is the diastolic blood pressure. This is the pressure in the artery at the end o diastole–that is, when the heart muscle is most relaxed. Perhaps surprisingly, it is the diastolic pressure that reveals most about the condition o the circulatory system. Having Ha ving a persistently high diastolic pressure is known as hypertension. Medical opinion o  exactly what consitutes hypertension is divided, but in general it is considered co nsidered to be anything above 140/90 (140 is the systolic pressure, pressure, and 90 the diastolic pressure). Long-term hypertension greatly greatly increases the risk o suering rom a myocardial myocardial inarction or stroke. Hypertension has numerous causes and risk actors. It is generally associated with atherosclerosis atheros clerosis,, and so obesity and diet are involved. invol ved. A high salt intake and smoking cigarettes (pages 276–278) also increase the risk o  developing hypertensi hypertension. on.

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SAQ 

5 A study ollowed 639 people with a amily history o CHD over a period o 14 years. Some had an LDL : HDL of more than 8, while some had an LDL : HDL of less than or equal to 8. The graph shows the probability of survival of a person in each of these groups over the 14 years of the study. LDL >8 HDL

100

Even Ev ents ts du duri ring ng st stud udy y per perio iod d

LDL ≤8 HDL 90

   %    /    l   a   v    i   v   r   u    S

80

70 0

254

2

4 6 8 10 Years rom start o study

12

o the people had been given 40 mg o statin each day over this period. The other hal were given a placebo–a pill that looked like a statin pill but did not contain any drug. Neither the people in the trial, nor the researchers who collected and analysed the results, knew which people were taking the statin and which were taking the placebo. The table shows the results.

14

Given Give n statin

Given placebo

total number o people who died

13 28

1 507

number who died rom CHD

5 87

707

number who died rom other circulatory diseases

1 94

230

number who suered a rst, non-atal heart attack

8 98

1 212

a Explain why the survival probability is 100% at 0 years. b Suggest why the graph is drawn so that it goes down in steps rather than in a smooth line. c Describe the conclusions that can be dra drawn wn rom these data. 6 Statins are drugs that inhibit an enzyme in liver cells which catalyses one o the reactions involved involv ed in the synthesis o cholesterol. In July 2002, the results o a ve-year study, study, involving more than 20 000 people, were published. Hal 

a Suggest why those people who did not take statins were given a placebo. b Suggest why the trial was organised so that the researchers interacting with the people, and collecting the results, did not know who was given statins and who was taking the placebo. c Discuss what the results suggest about the eectiveness o statins in reducing the risk o  developing coronary heart disease disease.. d Suggest how statins bring about the eects you have described in c.

Stroke A stroke is an acute instance o damage to the brain, caused by problems with the blood vessels supplying it. About 80% o strokes are caused by a blood clot that orms in a vessel as the result o  atherosclerosis. The remaining 20% are caused by bleeding into brain tissue (Figure 12.11). The risk actors or stroke are, as might be expected, the same as those or coronary heart disease. A person with hypertension has a considerably considerabl y increased risk o strok stroke. e. The risk

doubles with each 1 kPa (7 mm Hg) rise in diastolic blood pressure. Brain cells have a metabolic rate, and must have ha ve good supplies o oxy oxygen gen and glucose or respiration. They begin to die i deprived o these or more than a ew minutes. The eects o the stroke will depend on the parts o the brain in which neurones die. For For example, a stroke in the right side o the cerebrum is likely to aect movement on the let side o the body. body. As this side o the brain is concerned with spatial

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Proving the link For many years, doctors have urged people with high blood pressure to eat less salt, to decrease their risk o developing coronary heart disease or having a stroke. But there was no hard evidence to support this recommendation. Despite doctors’ and scientists’ suspicions, no-one had actually shown that reducing the salt in your diet is good or your health. Because the evidence was so shaky (and some people suggested that the little evidence there was even showed that a low-salt diet was bad or you) many people did not ollow their doctor’s advice. It was not until April 2007 that a careul piece o research actually showed that this link

genuinely exists–yes, exists–yes, eating less salt really is good or your health. The research ollowed ollowed 2400 people with high blood pressure–all volunteers–over a period o  15 years. Hal were shown how to look or lowsalt oods when they were shopping, and eat a low-salt diet, while hal ate a ‘normal’ diet, with as much salt as they wanted. The results showed that those eating a lowsalt diet had a 20% lower risk o death rom all causes. In all, 200 people had developed cardiovascular cardiov ascular disease. O these, 112 came rom the group that had not been recommended to eat a low-salt diet. Only 88 were in the low-salt group.

Exercise and health Numerous studies show that taking regular exercise has very great benecial eects on health. It reduces the incidence o chronic diseases such as coronary heart disease and Type 2 diabetes. It aects processes in the brain, and in most people it makes them eel happier, more energetic and more positive about their lives.

Aerobic exercise

Figure 12.11 CT scan o a section through the head o a woman who has suered a stroke on the let side o the brain.

awareness, the person may have problems with  judging distance and so nd diculty with walking walking or picking up objects objects.. A stroke in the let side o  the cerebrum will aect language language.. Memory is oten harmed no matter which side o the brain the stroke aects.

Muscles need oxygen and an energy source such as glucose to provide them with the ATP they need or contraction. The oxygen is used to allow aerobic respiration respiration to take place. I oxy oxygen gen is not supplied to the muscles ast enough, they can get by on anaerobic respiration or a while. But this produces lactate (lactic acid), and as this builds up the muscles stop working. An endurance athlete is thereore limited in his or her perormance by the rate at which oxygen can be supplied to the muscles. The harder the muscles are working, the aster the rate at which they use energy, and thereore the aster the rate that oxygen must be supplied to them. Marathon runners will try to run at the maximum speed that they can keep up or several hours. Their training increases the ability o the heart and lungs to get oxygen to the muscles as ast as possible over a

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long period o time. Even i you have no intention o becoming a marathon runner, runner, your tness and general health will almost certainly benet rom regular aerobic is, exercise in which which the muscles get exercise –that is, most o their energy rom aerobic respiration. respiration. It can take almost any orm you like to mention, so long as it is done at a rate that you can keep up or a reasonable amount o time time.. Walking, swimming, swimming, dancing and cycling, as well as long-distance running, are all orms o aerobic exercise (Figure 12.12).

Short-term eects o aerobic exercise The ways in which aerobic exercise aects the circulatory and gaseous exchange systems are summarised in Table 12.3.

Eects on the circulatory system When you are about to start exercising, your brain sends nerve impulses along a sympathetic nerve to the sino-atrial node (SAN)–the heart’s pacemaker–stimulating pacemaker–stim ulating it to contract at a aster rate. So your heart starts beating aster even beore you have begun the exercise. You might also begin to secrete more o the hormone adrenaline into the blood, which has the same eect on the heart as the sympathetic nerve. Once exercise begins, and the muscles are respiring at a aster rate rate,, cardiac output is urther increased. This is brought about by nitric oxide, a gas which acts as a hormone. When muscles are using up oxy oxygen gen quickly, the concentration o  oxygen oxy gen in the blood vessels in the muscles alls, and the cells in the blood vessel walls respond to the lowered oxygen oxygen concentration by secreting nitric oxide.. The nitric oxide makes the muscles in the oxide walls o arterioles relax, which widens the lumen o the arterioles (vasodilation) and allows more blood to fow through and more quickly. This in turn increases the rate at which blood fows back to the heart in the veins. The heart is designed so that it pumps out blood at the same rate that blood fows into it. (You can imagine what might happen i it did not do this this.) .) So extra blood fowing in, stretching the muscles in the heart wall, causes the heart to contract more 256

Fouillole Figure 12.12 Students on campus at Fouillole University Pointe a Pitre Grande Terre Guadeloupe, French West Indies. Walking and running are the two most common methods o  taking eective aerobic exercise. Eect o aerobic exercise exercise Circulation

more nerve impulses to the heart pacemaker, increasing heart rate more adrenaline secretion, increasing heart rate nitric oxide secretion, dilating arterioles,, which increases blood arterioles fow back to the heart and increases cardiac output diversion o blood to muscles by changes in dilation o arterioles dilation o arterioles supplying skin capillaries, increasing heat loss rom the skin

Gaseous exchange

breathing rate increases tidal volume increases increases in the acidity o  the blood are detected by chemoreceptors; inormat inormation ion is then sent to the brain, which increases rate and extent o  diaphragm and intercostal muscle contractions

Table 12.3

Short-term eects o exercise.

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orceully. This increases the stroke volume –the volume o blood orced out o the heart each time the ventricles contract. The stretching also stimulates the SAN, increasing the rate at which it res o nerve impulses. The blood vessels in various parts o the body also respond to the increased demand or oxygen and glucose by the muscles. We have seen that arterioles in the muscles widen (dilate). At the same time, arterioles supplying blood to other parts o the body whose needs are less urgent, such as the digestive system, contract and reduce blood fow. This allows more blood to fow to the muscles. muscles. At rest, the percentage o the blood fowing through the muscles is around 20%, but during strenuous exercise it can be over 80%. All this muscular activity generates a lot o  heat in the body. It is important that it can escape, and this is speeded up by dilation o the arterioles supplying blood to the skin surace surace.. This increases the rate at which heat is lost by radiation.

Eects on the gaseous exchange system Just as heart rate increases during du ring exercise, exercise, so does ventilation rate. rate. Breathing becomes aster and deeper, increasing the rate at which oxygen diuses into the blood in the lungs, and carbon dioxide diuses out. The increased rate o respiration in the muscles causes an increased quantity o carbon dioxide to diuse rom them into the blood. Chemoreceptors in the medulla o the brain and in the walls o the carotid arteries (which carry blood rom the aorta to the head) detect this by monitoring the pH o  the blood. A high concentration o carbon dioxide lowers the pH, making the blood more acidic. I a low pH is detected, nerve impulses will be sent rom the respiratory centre in the medulla to the intercostal muscles and the diaphragm muscles, making them contract harder and more quickly quickly.. This increases the rate at which new air is brought into the lungs and stale air removed, which in turn maintains a large concentration gradient between the alveoli and the capillaries. capillaries. At rest, ventilation rate may be about 10 dm3 min –1. During intense exercise,, values o well over 100 dm3 min –1 are exercise achieved.

SAQ 7 For each o the changes described in Table 12.3, explain how they help the body to cope with aerobic exercise.

Investigating the immediate eects o  exercise on the body A convenient type o exercise to carry out is a step test. This has the advantage that it can be done in exactly the same way by dierent people, or by the same person at dierent times. times. A platorm o some kind – a gym bench or a rmly positioned chair – is required. The height o the platorm is usually between 10 cm and 25 cm high. The person being invest investigated igated rst rests or several minutes, minutes, and their resting pulse rate is measured at least twice. They then step up and down onto the platorm a given number o times times,, or until they are exhausted. Their pulse rate is then measured again every minute ater the exercise has stopped, until it has returned to normal. I a metronome is available, then the rate o  stepping can be controlled. The metronome is set to a particular number o beats per minute (or example, example, 24 steps per minute) and the person matches their stepping to this rhythm.

Long-term eects o aerobic exercise Taking regular aerobic exercise over a long period o time can cause major changes to take place in the muscles muscles,, circulatory system and gaseous exchange systems. systems. The magnitude o these changes is, in general, proportional to the amount and intensity o training that is done. However, However, dierent people can respond very dierently to identical training, and there seems to be a strong genetic component to this this..

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Changes in the muscles Many changes take place in the muscles that are used in training. These changes are specic–they do not aect other muscles muscles.. They include: an increase in the cross-sectional area o  • slow-twitch slow-twit ch muscle bres (see page 259) This increases the mass o muscle that can be used during aerobic exercise, exercise, as well as increasing the overall size o the muscles. muscles. an increase in the number o capillaries in the • muscle,, and also in the ratio o capillaries to muscle muscle bres. bres. This increases the volume o  blood in the muscle, improving oxygen supply. an increase in the concentration con centration o myoglobin in • the muscle. Myoglobin is a respiratory pigment that stores oxygen, so this increases the amount o oxy oxygen gen stored within the muscle. an increase in the number and size o  • mitochondria in the muscle bres and thereore an increase in respiratory enzymes. Mitochondria are the sites where the Krebs cycle and oxidative phosphorylation occur, so this increases the rate at which these processes can occur within the muscle. an increase in the glycogen stores, which can • be rapidly broken broken down to glucose or use as a respiratory substrate. Changes in VO2 max and the circulatory system When a person increases the rate at which they are exercising, their rate o oxy oxygen gen consumption increases too. However, there comes a point where they can no longer get any more oxygen to their muscles,, or where their muscles just cannot use muscles oxygen any aster, at which point the muscles have to switch over to anaerobic respiration. The maximum rate at which oxygen is used, beore the muscles have to make the switch, is called VO2 max. VO2 max increases with training. A trained athlete can have a higher work rate beore their muscles switch to the less energy-ecient anaerobic respiration. respiration. The changes in the muscles described above contribute to this. Changes in the cardiovascular system also contribute to this

258

improvement, by increasing the rate at which oxygen can be supplied to the muscles muscles.. The changes include: an increased number o red blood cells. This • increases the ability o the blood to carry oxygen. an increase in the size o the heart muscle, • especially in the walls o the let ventricle. This increases the orce with which the muscle can contract and orce blood out o the heart. an increase in stroke volume –that is, is, the volume • o blood that is orced out o the heart with each beat. an increase in cardiac efciency –that is, is, the work • output that the heart produces or each unit o  oxygen that it uses. As a result o these changes, the heart rate o the trained person decreases when they are resting, because the greater stroke stroke volume means that the same quantity o blood can be moved around the body using a slower heart rate. However, the maximum possible stroke volume is considerably increased, so the person can exercise harder and still manage to get enough blood into their muscles to supply the oxygen that they need. The heart rate recovery period–that is, is, the time taken or the heart rate to return to normal ater exercise–decreases with training. This is oten used as a good measure o how a person’s person’s tness is improving during a training programme.

Changes in the gaseous exchange system Training increases the rate at which oxygen can be brought into the body and carbon dioxide removed. Everyone’s breathing rate and depth increase when they exercise, but the degree to which this happens is impro improved ved by regular aerobic training. For example, while a ‘normal’ person might be able to increase their ventilation rate by up to ten times, a really really t endurance athlete may be able to increase theirs by as much as 20 times. Top Olympic-standard rowers may have ventilation rates o 200 dm3 min –1. Maximum oxygen intake is also achieved more quickly in a trained person.

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Slow-twitch and ast-twitch muscle fbres There are two dierent types o muscle bres in the skeletal muscles in the human body. They are known as slow-twitch and ast-twitch bres. During aerobic exercise, it is mostly the slowtwitch bres that are working. These bres b res are adapted or continuous aerobic respiration. They contain a lot o myoglobin, which makes them look dark red, so they are sometimes known as ‘red bres’.

During intensive, short-term exercise, such as sprinting, the ast-twitch bres are used. They are adapted or producing ATP by anaerobic respiration. They thereore thereore do not require stores o oxygen, and do not contain much myoglobin. They are sometimes known as ‘white bres’. See i you can explain how each o the structural dierences between slow-twitch and ast-twitch bres, shown in the diagram, adapt them or their dierent ways o generating ATP.

Slow-twitch fbres

Fast-twitch fbres

produce ATP through aerobic respiration

produce ATP through anaerobic respiration

contain large numbers o  mitochondria

contain ew mitochondria

contain large quantities o  myoglobin

contain little myoglobin have a relatively large diameter  (about twice that o a slow-twitch fbre)

have a relatively small diameter 

are supplied by relatively ew capillaries are supplied by large numbers o capillaries

SAQ 

8 A group o untrained people undertook a training programme involving aerobic exercise over a period o 13 weeks. The graph shows the mean VO2 max o these people during the training period. a Explain the meaning o the term ‘VO2 max’. b Describe the changes in VO2 max during this training programme. c Suggest reasons or the changes that you describe.

3.8    1    −

  n 3.6    i   m    3

  m3.4    d    /   x   a 3.2   m    2

   O3.0    V

2.8

0

2

4 6 8 10 Weeks of training

12

14

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SAQ 

9 During aerobic exercise, most respiration taking place in the muscles is aerobic. However, even at low rates o exercise some anaerobic respiration respiration also happens. 12

  n   o    i    t 10   a   r    t   n   e   3 8   c   n   m   o   d   c   l 6   e   o    t   a   m    t   m4   c   /   a    l    d   o 2   o    l    B    −

0 50

before training

after  training 100 150 200 250 300 350 Power output / W

A person undertook a programme o aerobic training. The graph shows the relationship between the intensity o exercise, measured as power output in watts, and the concentration o 

Inectious diseases There are many inectious diseases that can cause serious illness. In the Caribbean, two inectious diseases that are having a considerable impact on society are HIV/AIDS HIV/AIDS,, and dengue ever.

The eects o HIV/AIDS on society We have already looked at HIV/AIDS in some detail. In Chapter 10, we described how the human immunodeciency virus is transmitted rom one person to another, and looked at its lie cycle. In Chapter 11 we saw how the virus aects the immune system and causes AIDS. Unlike most diseases, it is people in the prime o their lives who are most likely to be aected by HIV/AIDS,, and most likely to die as a result o  HIV/AIDS this inection. This means that many children are let with no parents to care or them. Older people, who depended on their grow grown-up n-up children or care and support, may lose this essential support to help them to continue to live independent lives. This puts an extra burden on the State and on

260

lactate in the blood or this person beore and ater the training programme. a i Describe the relationship between blood lactate concentration and intensity o  exercise, up to a power output o 175 W. relationship. ii Suggest reasons or this relationship. b The lactate threshold is the point at which more lactate is being produced than can be cleared rom the blood. i Name the organ o rgan that is responsible or breaking down lactate. ii Use the graph to determine the power outputs at which the person reached their lactate threshold beore training, and ater training. iii Explain three changes in the body that could contribute to this increase in the lactate threshold ater training. c Explain how an increase in lactate threshold could improve the perormance o an endurance athlete such as a rower or marathon runner.

charities, who have to step in to care or people who have have lost essential members o their amilies. amilies. The workorce workorce o the Caribbean is also aected, as many people who would be important members o the working community can no longer continue to do their jobs normally. HIV/AIDS is a signicant drain on the resources available or healthcare. Money is spent on education, testing and diagnosis (or example, all pregnant women are routinely tested or HIV) and treatment. Where drugs are available, they will need to be taken or the rest o a patient’s patient’s lie.

Dengue ever  Dengue ever is a disease caused by a virus. The virus is transmitted by the mosquito Aedes aegypti . These mosquitoes are thereore vectors or dengue ever. The dengue ever virus, oten abbreviated to DENV,, belongs to a amily o viruses called DENV faviviruses fa viviruses.. The structure o o  a mature virus particle is shown in Figure 12.13, and the way in

Chapter 12: Social and preventative medicine

which the virus reproduces inside human cells is shown in Figure 12.14. There are several dierent orms (serotypes) o the virus and, unortuna unortunately tely,, immunity against one orm does not provide immunity against the others others..

virus envelope–  modifed plasma membrane taken rom a human cell

virus capsid–a protein coat

RNA–carries code or making new viruses

proteins that attach to human cells to help the virus invade

proteins that catalyse stages in virus replication

25 nm

The dengue virus

Figure 12.13

1 Virus attaches to a human cell. Proteins on the virus link with proteins on the plasma membrane.

2 Virus enters the cell in an endosome.

3 The virus breaks down. Its RNA is released.

4 The virus RNA controls the synthesis o new virus components, using the cell’s RER.

Figure 12.14

Dengue ever was originally conned to tropical countries, countries, but recently it has h as been spreading to countries urther north and south o  the equator. Figure 12.15 shows the distribution o dengue ever in the Americas in 2006. Dengue ever is a serious disease in the Caribbean, and in some years, such as 2010, the numbers o  inections rise to epidemic proportions. proportions. The number o cases o dengue ever are increasing worldwide, world wide, and it is considered to be a serious public health problem. In 2010, there were 30 times more cases worldwide worldwide than in 1960. Noone is quite sure why this is, but it may be a combination o the greater number o people travelling tra velling around the globe, and global warming increasing the breeding range o the Aedes aegypti  mosquitoes.

Inection with the dengue virus The A. aegypti mosquitoes aegypti mosquitoes that transmit the dengue virus breed in any small pools o water that they nd–or example, in old tyres, water storage containers and old oil drums. This means that they are present in both cities and in rural areas.. The mosquitoes are most active during the areas day, especially at dawn and dusk, which is when 8 The fnished virus takes some o the cell’s plasma membrane with it and it is modifed to orm the envelope o the virus. 7 Vesicles containing the partly assembled virus particles move towards the plasma membrane and leave the cell. 6 Partly assembled virus particles are transerred to a Golgi body.

5 Virus components begin assembly within membrane compartments.

Replication Replica tion o the dengue virus.

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eectively, but instead harbour viruses that actually continue to duplicate themselves inside the cells. These cells, and other white blood cells attacked by the viruses, accumulate in the lymph nodes. The antibody production also causes the prolieration and action o T-killer cells (T-cytotoxic cells) that carry receptors matching the viral antigens. The role o these cells is to kill inected or abnormal cells, but they are not particularly eective against cells invaded by this virus.

6143–346550 2040–6143 22–2040 0–1 no data

Figure 12.15 Distribution o dengue ever in the Americas (number o cases in 2006).

they are most likely to bite a person. Female A. aegypti mosquitoes aegypti mosquitoes eed on blood. When they bite, they inject saliva, which contains an anti-clotting agent and thereor thereoree enables the blood to fow reely into their mouthparts. When an inected mosquito bites a person, the virus enters the person’s body in the mosquito’s saliva. The virus can enter many dierent types o  cells in the skin. The proteins in the outer coat o the virus can bind to proteins in the plasma membranes o the skin cells, allowing the virus to enter the cells. The entry o the virus stimulates the body’s immune system into action. Cytokines are produced, which stimulate the generation o  antibodies by B-lymphocytes. Some o the antibodies bind to the viral proteins, which causes phagocytes to engul the viruses. Unortunately, in many cases the phagocytes do not kill the virus

262

Symptoms and treatment Dengue ever is an unpleasant illness, with symptoms similar to infuenza. The person has a high temperature, a rash, a severe headache and pain in the muscles and joints. They may eel sick and vomit, and probably will not want to eat. The illness generally lasts up to 10 days, but many people will not eel ully better or up to one month. Although dengue ever is very unpleasant, it is not a particularly dangerous illness. However, in some cases a much more serious condition develops,, called dengue haemorrhagic ever. This develops results rom damage to the cells lining the blood vessels (the endothelium), and disruption o the normal blood-clotting process. Fluid leaks rom the blood vessels and accumulates in the tissues tissues.. This may happen in many dierent organs, and can result in very serious illness that is atal in about 5% o cases. As or many viral diseases, there are no drugs that can be taken to kill the dengue ever virus. (Antibiotics only work against bacteria, not viruses.) viruses .) Treatment Treatment consists o making the person as comortable comortable as possible possible,, and ensuring en suring that they continue to take plenty o fuids, especially i they are losing liquid through vomiting. This can oten be done at home, but in serious cases the person may need to be connected to an intravenous drip in hospital. Paracetamol can be taken to reduce the pain, but aspirin and ibuproen should be avoided, because they can worsen the bleeding that may occur. occur. The great majority o people make a ull recovery recovery..

Chapter 12: Social and preventative medicine

Prevention As yet, no vaccine has been developed to immunise people against dengue ever ever.. Researchers are currently working on this, trying to produce a vaccine that will protect people against all the dierent orms o the virus. There are already already some possible vaccines undergoing trials, and there is hope that there could be a useul vaccine available by as early as 2015. For the moment, however, the only way to prevent yoursel yoursel getting dengue ever is to avoid

being bitten by the A. aegypti mosquitoes aegypti mosquitoes.. I  you know that you are in an area where dengue ever is present, you can use insecticides such as DEET on your skin to deter the mosquitoes, and wear clothing that covers your arms and legs. Everyone can help by clearing up rubbish that may collect water and pro provide vide breeding grounds or the mosquitoes. Another approach, useul with larger bodies o water water,, is to introduce sh or other organisms that will eed on the mosquito larvae.

Summary Obesity is dened as ha having ving a body mass index greater than 27. Being obese increases the risk o  developing Type Type 2 diabetes diabetes.. People become obese through eating a diet that contains more energy than their body uses uses..

•

Atherosclerosis is a condition that develops when the walls o the blood vessels lose their elasticity. Atherosclerosis elasticity. I this happens in the coronary arteries, a person has coronary co ronary heart disease (CHD). Atherosclerosis Atherosclerosis develops as plaques orm in artery walls, due to the build-up o cholesterol.

•

A diet rich in saturated ats increases the risk o developing CHD. Having Having a low ratio o HDL : LDL cholesterol also increases this risk.

•

Hypertension (high blood pressure) is oten associated with atherosclerosis. atherosclerosis. Other risk actors include a diet containing a lot o salt, and smoking cigarettes. Hypertension increases the likelihood o  developing CHD, CHD, and also o o  suering a stroke. stroke.

•

Aerobic exercise helps to maintain tness. Regular exercise increases the maximum rate at which oxygen can be used by the body, known as VO2 max, and cardiac eciency eciency.. Exercise can help to maintain body weight at a healthy level, and reduce the risk o the development o chronic diseases such as Type 2 diabetes.

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AIDS and dengue ever are serious inectious diseases that are caused by viruses. The dengue ever virus is transmitted by the mosquito vector Aedes aegypti . The mosquitoes breed in any body o  water,, so an important method o control is to remove rubbish in which water water water may collect, or to add predators o mosquito larvae to ponds.

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Questions Multiple choice questions 1 Which o ollo ollowing wing best describes a ‘balanced diet’? A one which provides an adequate intake o nutrients needed or maintenance o body and good health B one which contains co ntains carbohydrates, carbohydrates, lipids and proteins C one which provides an adequate intake o energy and nutrients needed or maintenance o  body and good health D one which provides an adequate intake o energy needed or maintenance o body and good health 2 One way o dening obesity is by the Body Mass Index (BMI). The ormula or BMI is: body mass in kg A height in metres body mass in g B height in metres (height in metres)2 C body mass in kg body mass in kg D (height in metres)2 3 Image I shows a healthy coronary artery while image II shows the artery when it became unhealthy. I

II

What is the name o the disease and a cause that is characterised by image II? A coronary heart disease–diet high in saturated ats B plaque ormation–diet high in cholesterol C ather atherosclerosis–diet osclerosis–diet high in sh oils D coronary heart disease–diet high in unsaturated ats 4 Which o the ollowing is not an immediate eect o exercise on the body? A increased heart rate B vasoconstriction in skeletal muscles C rise in blood pressure D vasodilat vasodilation ion in skeletal muscles continued ...

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5 A girl has been running every day to improve her level o physical tness. tness. Which o the ollowing is a long-term benet to the girl in improving her physical physical tness? A less glycogen and at stored in skeletal muscle B reduction in blood cholesterol concentration C increase in number o alveoli in lung D reduction in tidal volume at rest 6. What is the causative causative pathogen o dengue ever? A protoctist B bacterium C virus D ungus 7 What is the vector o dengue ever? A the emale Aedes aegypti mosquito aegypti mosquito B the male Aedes aegypti mosquito aegypti mosquito C the emale Anopheles mosquito D the male Anopheles mosquito 8

Which o the ollowing is not a method by which HIV is transmitted? A rom mother to child across the placenta B receiving blood through transusions sterilisation on C sharing needles without sterilisati D sharing eating utensils

9

Which o the ollowing is an impact o HIV/AIDS in the Caribbean region? A It has little eect on the work orce. B It is not a major cause o death in the region. C It does not drain resources or education. D It has improved educational awareness awareness o sexually transmitted disease. disease.

10 Which cells o the immune system are susceptible to HIV? A T helper cells with CD8 receptors B T cytotoxic cells with CD4+ receptors C T helper cells with CD4+ receptors D T cytotoxic cells with CD8 receptors

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Structured questions

What are the components o a balanced diet? 11 a What b Obesity is now a global problem. i Dene the term ‘obesity’. obesity.. ii Explain how poor diet can lead to obesity iii A man is 1.65 m tall and weighs 82 kg. Calculate his Body Mass Index (BMI). Show calcul calculations. ations. iv Comment on the BMI value obtained in iii. diabetes. c Obesity is linked to many diseases including diabetes. i Distingu Distinguish ish between Type 1 and Type 2 diabetes. ii Explain how obesity is linked to Type 2 diabetes. deter mine their cardiovascular eciency by 12 a Students perormed an experiment to determine observing their pulse rates during various activities. They rst took their resting pulse rate,, then perormed various activities. rate activities. The duration o the stepping exercise was 3 minutes. i Wha Whatt do you understand by the term ‘resting pulse rate’? ii Explain wh why y resting pulse rate is taken as a measure o one’ one’ss physical tness tness.. Why y was the resting pulse rate taken beore the exercise began? iii Wh iv Suggest how the students could use a step test during this experiment. Students were provided provided with with a stepping stool o 4 cm, a stopwatch stopwatch and a digital pulse meter. meter.

[3 marks] [1 mark] [3 marks] [2 marks] [1 mark] [2 marks] [3 marks]

[1 mark] [2 marks] [2 marks] [3 marks]

The results below are rom one o the students rom the class. Activity Pulse rate per minute

At rest

76

Standing

Exercise

Recovery ater 1 min

101

13 0

89

v Using the ormula below, calculate the student’s cardiovascular eciency.

cardiovascular cardiov ascular eciency =

duration o exercise in seconds × 100 recovery pulse × 5.6

vi Using the inormation below, assess the studen student’s t’s cardiovascul cardiovascular ar ecienc eciency y. Cardiovascular Cardiov ascular eciency is assessed as: 0–27 = very poor 28–38 = poor 39–48 = air 49–59 = good 60–70 = very good 71–100 = excellent body.. b State three short term eects o exercise on the body c State three long term eects o exercise on the body 13 HIV is described as a retro retrovirus virus and is transmitted in a variety o wa ways. ys. described ed as a retrovirus. a Explain why HIV is describ b Describe three ways in which HIV is transmitted. c The gure below shows the inection cycle o HIV in a T helper lymphocyte.

[2 marks] [1 mark]

[3 marks] [3 marks] [1 mark] [3 marks]

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The table below describes the various steps o the inection but they are not no t in order.

1

8 7 2 6 3 4

5

1– 8 8. Identiy stages 1–  Description

Stage

reverse transcription: making o DNA copy rom viral RNA transcription: special enzymes create mRNA binding: attachment o HIV proteins to CD4+ surace receptor o  T helper cell viral assembly and maturation: new viral particles are assembled and become more inectious translation: new viral proteins are produced budding: T-helper cell lyses and releases inectious new viral cells RNA rom virus is released into T helper cell integration: HIV DNA is added into the cell’s DNA using viral enzyme, integrase [4 marks]

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d The drug therapy that is employed to treat people inected with HIV is known as HAART (highly active anti-retroviral therapy). This therapy contains a combination o drugs which target dierent stages o the viral inection cycle. Suggest two ways that these drugs may slow the onset o HIV HIV.. e AIDS is the nal and most serious stage o HIV inection. What are the signs indicating that this stage has been reached?   Explain why why the number o people who are inected with HIV is usually greater than the number o people with AIDS.

[2 marks] [2 marks] [3 marks]

Essay questions

cardiovascular ascular system. 14 a Discuss the eects o ats on the cardiov vessels.. b Explain how plaque is ormed in blood vessels 15 a b c d

Using a graph, explain what is meant by the term ter m ‘VO2 max’. What actors may infuence a person’s VO2 max? Suggest how a person may improve their VO2 max. A ootballer has reached his VO2 max. Suggest what happens to his muscles i he continues playing.

16 Both HIV/AIDS and dengue are diseases that have have both social and economic impact on the Caribbean region. a Discuss the transmission, incubation period, symptoms and prevention o dengue. b HIV inections can lead to AIDS. Describe three symptoms o AIDS. c Discuss the impact o AIDS and dengue in the Caribbean.

268

[10 marks] [5 marks] [4 marks] [4 marks] [4 marks] [3 marks]

[8 marks] [3 marks] [4 marks]