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Senior Science

9.3 Medical Technology – Bionics

Section 2

MaintainingBlood Flow

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9.3 Section 2 ::: Maintaining Blood Flow

9.2 The regular beating of the heart and continuity of the flow of blood through the heart and around the body is needed to maintain good health

9.3.2 a Explain the relationship between the structure and function of the following parts of the heart

– Valves– Atria– Ventricles– Major arteries and veins

9.3.2 b Explain that specialised tissues in the heart produce an electrical signal that stimulates rhythmic contractions of the cardiac muscle

9.3.2 c Discuss the problems that can result from interruptions to the normal rhythm of the heart

9.3.2 d Identify that a pacemaker will produce a regular electrical impulse

9.3.2 e Identify the types of materials used to make pacemakers and the properties that make these suitable for implanting in the body

9.3.2 f Describe the problems that can result from faulty valves in the heart

9.3.2 g Describe the properties of materials such as Teflon/pyrolytic carbon that make them versatile materials for making artificial body parts, including heart valves

9.3.2 h Describe and explain the effects of a build up of plaque on the walls of major arteries and veins on blood flow to and from the heart

9.3.2.i Discuss ways in which plaque could be eliminated or altered to ease blood flow


9.3.2. i Gather, identify data sources, plan, choose equipment or resources for, perform a first-hand investigation and analyse information about changes in the heart beat rate before and after sustained physical activity

9.3.2 ii Plan and perform an investigation to identify individual aspects that comprise the heart beat

9.3.2 iii Identify data sources, gather, process and analyse information to outline the historical development of pacemakers and use available evidence to identify types of technological advances that have made their development possible

9.3.2 iv Construct a simple model to demonstrate the function of valves in the heart

9.3.2 v Gather, process and analyse information to outline areas of current research in heart transplants and/or artificial hearts and their impact on society

9.3.2 vi Gather information from secondary sources on techniques used, including angioplasty, to ease blood flow to and from the heart and in blood vessels, when there has been a build up of plaque

9.3.2 vii Process information to identify different types and functions of artificial valves in the heart


Introduction

The Human Circulatory System consists of a heart and three types of blood vessels – arteries, capillaries and veins. An artery is a blood vessel taking blood away from the heart. A vein is a blood vessel carrying blood to the heart. A capillary is a tiny blood vessel that joins arteries and veins. The exchange of materials into and out of the blood takes place across the thin walls of the capillaries.

A description of one circuit of the circulatory system is written below.

Blood returns to the heart from body tissues.

It enters the right atrium (upper right chamber of the heart).

The heart contracts pumping blood into the right ventricle (via the tricuspid valve).

The right ventricle contracts pumping blood towards the lungs (via the pulmonary valve).

The blood travels to the lungs via the pulmonary artery.

It then enters the lung capillaries where it releases carbon dioxide and collects oxygen.

The blood then travels back to the heart via the pulmonary vein.

It enters the left atrium (upper left chamber of the heart).

The left atrium contracts pumping blood into the left ventricle (via the bicuspid valve).

The left ventricle contracts pumping blood into a large artery, the aorta (via the aortic valve).

The aorta branches several times to send blood to all parts of the body.

The blood enters capillaries in various parts of the body.

In the capillaries the blood releases oxygen into the body tissues and collects carbon dioxide.

The blood returns from the body to the heart via the veins (vena cavas).

It enters the right atrium (upper right chamber of the heart).


Role of the Circulatory System

The role of the circulatory system is to function as a transport network throughout the body. As such particular functions of the circulatory system are: It transports oxygen from the lungs to body cells It transports carbon dioxide from body cells to the lungs It transports nutrients (digested food) from the small intestine to body cells It transports wastes from body cells to the excretory organs for elimination. It distributes heat energy produced by body muscles to all areas of the body. It carries white blood cells that are important in fighting disease.

Notes Questions

1. Name the three blood vessels in the circulatory system.

2. When blood flows around the body it passes through various parts of the circulatory system. Put the following parts of the circulatory system in the correct order.Right atrium Veins (vena cavas) Left ventricle Pulmonary veinLeft atrium Pulmonary artery Aorta Lung capillariesRight atrium Right ventricle Body capillaries

3. Name the four valves in the heart

4. Name five things transported by the circulatory system


9.3.2 i Gather, identify data sources, plan, choose equipment or resources for, perform a first-hand investigation and analyse information about changes in the heart beat rate Before and after sustained physical activity

Activity 2– 1 Exercise and Heart Rate

The task is to investigate changes in the heart beat rate during rest and during sustained physical activity. This will require students to: Gather, Identify data sources, Plan, Choose equipment or resources for, Perform a first-hand investigation and Analyse information gathered

Planning

Information to consider What to doDiscuss the information and questions below. After the discussion plan your investigation.

Define pulse rate.Describe how to measure pulse rate.Caution about risks involved in exercising.Should subjects warm up before exercising?Work in pairs – one exercising, one recordingClearly state when pulse rate is measured?How long will heart rate be measured?Is pulse rate measured before, during and after exercise?How many times after exercise is pulse rate measured?Describe the physical activity to be used, in such a way that it can be repeated.Clearly state how long the subjects exercise?State measurements that need to be repeated.How many subjects will exercise?Record results in a table

1. Write a heading for the investigation.

2. Write an aim for the investigation.

3. List possible risks associated with exercising

4. Make a list of equipment needed.

5. Write a method for the investigation.a. List the instructions to be followed

for each test, in point form.

6. Tabulate results [A sample is shown]

7. Graph results

8. Write a conclusion


Results

A table like the one below can be used for the results.

Before Exercise After Exercise (minutes)1 2 3 0 1 2 3 4

Beats for 10 secs.

Beats for 1 min.PULSE RATE

Conclusion

Write an appropriate conclusion for this investigation

Discussion

1. Evaluate the validity of the data collected. [5 marks]2. Evaluate the appropriateness of the method used to solve the problem. [5 marks]

Marking criteria for Plan – Exercise and Heart Rate [12 marks]

Syllabus Outcome – H11.2 Plan first – hand investigationsThe report should be written so that it is clear from reading the laboratory report that:1. The investigation is attempting to find if one Variable changes (dependent) because of the change

in another Variable (independent) [2]2. Some variables need to be kept constant [2]3. It is clear how the pulse rate will be Measured [2]4. The instructions for the Activity are: [3]

Easily followed - sequence of steps in a logical order. In point form and numbered (1st, 2nd 3rd etc) There is enough detail so that the investigation can be repeated.

5. Enough data will be collected so that results are reliable – Number [1]6. Safety issues are identified. [2]

Marking criteria for Final report – Exercise and Heart Rate [23 marks]Syllabus Outcome – H12.41. Evaluate the validity of the data collected (Discussion question). [5]

Syllabus Outcome – H13 Present information1. Use the laboratory report scaffold. [2]2. Data table used for results – column headings, units, ruled, data accurate [4]3. Line graph – drawn to scale, axes labelled, units, ruled, data accurate [5]

Syllabus Outcome – H14 Draws conclusion4. Identifies trends and relationships [2]5. Evaluate the appropriateness of the method used to solve the problem (Disc question). [5]


Discussion Questions [26 marks]

Syllabus Outcome – H11 -11.2 a,b,c,d, -11.3 a,b; H12 -12.2 b;

1. The dependent variable in this investigation is the amount of activity.Identify the independent variable? [1 mark]

2. Name TWO variables that need to be kept constant? [2 marks]3. Explain why all subjects need to do the same exercise. [2 marks]4. Name the TWO groups in the investigation. [2 marks]5. Describe how these TWO groups are the same. [3 marks]6. Identify what is measured in this investigation. [1 mark]7. Explain why the activity should be repeatable. [2 marks]8. Discuss the validity of the data collected in this investigation. [5 marks]9. Outline how the number of subjects makes this investigation reliable. [2 marks]10. Identify TWO risks in this investigation. [2 marks]

11.Discuss why heart rate changes as the level of physical activity changes. [4 marks]

Discuss (and evaluate) questions are unstructured and require an extended answer

In order to answer such a question, you must provide some structure. STEP 1 Identify (& highlight) the important words in the question

STEP 2 Recall definitions of these important words (if necessary) Discuss – identify issues and provide points for and against Validity –

STEP 3 Develop your own answer that reflects the depth required (Verb & marks)

The pulse rate varies greatly in individuals. The average rate for adults who are relaxed mentally and physically is about 65 – 70 in men and 70 – 75 in women. It is much higher in babies. The count slows during sleep. Withy mild exercise the pulse rate will increase gradually. It increases greatly when a person works hard or becomes very excited. The count may reach 200 per minute. Other conditions, such as surgical shock, haemorrhage, and fever also cause a marked increase in the pulse rate.


9.3.2 a Explain the relationship between the structure and function of the following parts of the heart

– Valves– Atria– Ventricles– Major arteries and veins

Parts of the Heart – Structure and Function

The heart is a large hollow muscle. Tubes called veins bring blood to the heart. Other tubes called arteries carry blood away from the heart. Regulators called valves control the flow of blood through the heart itself.

The heart consists of four chambers. The two chambers in the upper half of the heart are called atria (atrium). The atria are thin walled. They are relatively thin walled because of their functions. They only collect blood flowing into the heart from the body and then squeeze blood a short distance into the ventricles. Then the atria contract and squeeze blood through the tricuspid valve into the right ventricle and through the bicuspid valve into the left ventricle.

The two chambers in the lower half of the heart are called ventricles. The walls of the ventricles are made of thick, strong muscles. The right ventricle pumps blood a short distance to the lungs. The left ventricle has walls three times as thick as those of the right ventricle because it has to pump the blood so much further. The left ventricle pumps blood around the entire body.

Valves are made of flaps of thin, strong fibrous tissue. This allows them to rapidly open and close. Valves control the flow of blood through the heart. These flaps permit the flow of blood in one direction, but they prevent it from flowing back. They are like doors that open only in one direction. They respond to the pressure exerted by the blood.

The walls of the arteries are made up of three layers. The structure of each layer is related to its function. The outer layer consists of elastic tissue. Each time the heart beats, this layer stretches to make room for the blood that is being pumped through the artery. The middle layer is muscle (and elastic tissue). After the artery stretches, this muscular tissue contracts


and squeezes the blood further through the artery. This means the arteries do a lot of the work of pushing blood around the body. The inner layer, or lining, of the arteries is made of thin, smooth cells (these same cells line the heart, veins and capillaries). This reduces friction and allows blood to flow more easily.

Blood flow through the veins is smooth and continuous rather than in the bursts or pulses of the arteries. The pressure of venous blood is very low. Veins, like arteries, have walls made of three layers. The walls of the veins are thinner, less elastic, and less muscular than artery walls. To make it easier for blood to flow, veins are bigger than arteries and have a bigger bore. The flow of blood in veins is helped by the action of the muscles during movement. As well, in the bigger veins, the lining of the vein has folds that act like valves. Several things can cause the blood to slow down or stop – the weight of the blood, pressure on the vein, or low blood pressure. Then the valves open out, to stop the blood from flowing backward. The valves are usually just above the place where two veins join. Veins that are swollen, stretched, or coiled on themselves, are varicose veins.

Notes Questions

1. What do valves do?2. Name the two functions of the atria?3. Which chambers of the heart have the thickest walls (largest muscles)?4. Which chambers of the heart pump blood the greatest distance?5. Suggest a reason why valves are made from thin tissue.6. What is the function of valves?7. Why is the middle layer of an artery elastic?8. Why is the inner layer of an artery smooth?9. Which blood vessel has a pulse?10.Why do the bigger veins have valves?

11.Match the three columns in the table below.

Name Structure FunctionArteries have Flaps of thin, strong fibrous

tissueBecause it needs to pump blood around the whole body

Valves have Thick, strong muscles Because they reduce friction and allows blood to flow more easily

The wall of the left ventricle has

An inner layer made of thin, smooth cells

So they can rapidly open and close

Arteries have An elastic layer Because it squeezes blood around the body

Veins have A thick muscular wall that stretches to make room for the blood that is being pumped


9.3.2 b Explain that specialised tissues in the heart produce an electrical signal that stimulates rhythmic contractions of the cardiac muscle

Cardiac Rhythm

Muscles in the body contract in response to signals. These signals are small electric currents delivered by nerves attached to the muscle. The heart is composed of a special type of muscle, called cardiac muscle. It also responds to electrical impulses. The heart has a regular beat because specialised tissues in the heart produce an electrical signal that stimulates the rhythmic contractions of the heart muscle. These specialised tissues are called the Sinoatrial (S-A) node or pacemaker cells. They are located in the right atrium. This group of special conduction cells are capable of sending signals at a rate up to 300 times per minute.

The impulse from the S-A node spreads via special conducting tissue through the atria. The signals reach a second node, the atrioventricular (A-V node) at the bottom of the atrium. These signals then spread between the ventricles via the septum and then up to the outside muscles of the ventricles. This pattern of signals therefore co-ordinates contractions of the heart, so that the upper chambers contract first and then the lower chambers.

Notes Questions

12.What type of tissue carries small electrical currents to the muscles?

13.Name the cells that stimulate the rhythmic contractions of the heart muscle.

14.Does the whole heart contract at the same time? Provide some detail in your answer.


9.3.2 c Discuss the problems that can result from interruptions to the normal rhythm of the heart

Interruptions to the heart rhythm

What to do

Read the information below on interruptions to the heart rhythm.Use this information to write a discussion on the problems that can result from interruptions to the normal rhythm of the heart.

Blood supply is essential for the cells of the body to survive. The blood transports oxygen and nutrients to the cells and transports carbon dioxide and other wastes from the cells. For this to occur the supply of fresh blood needs to be regular. Under normal circumstances the rhythmic beating of the heart maintains a regular supply of blood to the tissues of the body.

The rate at which the heart beats will vary according to the need for increased circulation of blood around the body. Normal adult heart rates at rest are between 50 and 75 beats per minute. Females’ heart rates are usually higher than males. Also heart rates are fastest at birth and then slow with age.

There are other situations that will cause an increase in heart rate. Increased heart rate can be caused by: Exercise: There is an increased need for oxygen in the muscles during exercise so the

heart has to pump more blood to supply this demand. Emotion: Fear, anger and stress will affect the heart rate. Chemical substances: Adrenalin (a hormone produced in the body during stressful

situations) will increase heart rate. However, other substances such as alcohol, caffeine, tobacco and certain medications may cause abnormal heartbeats.

Blood pressure: If a drop in blood pressure should occur then the heart rate increases to restore blood pressure level.

Interruptions to the heart rhythm interfere with regular supply of blood. It therefore, interferes with the essential transport of substances to and from the body tissues. This in turn can cause tiredness, pain, and even heart attack and death.

Sometimes disease or degeneration of the conducting tissues in the heart can occur. This can be as a result of muscle degeneration, muscle damage (such as can occur in a heart attack) or when extra conduction pathways are present. This can affect the rhythm of the heartbeat causing abnormal beats (Arrhythmia) e.g. fibrillation - where the chambers start contracting rapidly in an almost chaotic way.


A doctor feels a patient’s pulse to find out if the heart is beating normally. If the pulse is too fast or too slow or irregular, the doctor then examines the patient to diagnose the cause of the abnormal pulse.

Arrhythmia is an abnormal heart rhythm. Arrhythmias often are an extra heartbeat that causes no serious problems. However, sometimes the heart rhythm can become dangerously slow or fast.

Abnormally slow heart rhythms can result in a loss of consciousness, heart failure or even death. The slow heart rate greatly reduces the amount of oxygen delivered to body cells. This abnormal rhythm can sometimes be controlled with medication. However, under some circumstances and artificial heart pacemaker may be needed. The slow heartbeat can occur if the sinoatrial node or the atria are damaged (sick sinus syndrome). Alternatively, a condition called heart block can occur in which the electrical impulses started by the heart’s natural pacemaker (the S-A node) fail to be conducted to the ventricles. This device transmits an electric impulse to the heart, stimulating it to beat in a normal rhythm.

Abnormally fast heart rhythms can also be the cause of disabling symptoms or death from heart disease. Such abnormal heartbeats can occur unexpectedly after a heart attack. Many can be controlled with medication. In serious emergencies, applying electric shock can treat them, but the shock must be administered within minutes to prevent severe heart damage. In some cases, doctors implant a defibrillator to detect and treat abnormally fast heart rhythms. The defibrillator monitors the heart and automatically delivers electric shocks before the arrhythmia causes permanent damage.

Notes Questions

15.What is the normal heart rate?

16.What happens to heart rate as a person gets older?

17.Name some situations that can cause heart rate to increase

18.Name three problems associated with interruptions to the heart rhythm.

19.What is arrhythmia?

20.Name two possible causes of arrhythmia.

21.Are all arrhythmias dangerous?

22.Why is a slow heart rate a problem?

23.What medical treatments are available for slow heart rhythms?

24.What does a defibrillator do?


9.3.2 d Identify that a pacemaker will produce a regular electrical impulse

9.3.2 iii Identify data sources, gather, process and analyse information to outline the historical development of pacemakers and use available evidence to identify types of technological advances that have made their development possible

9.3.2 e Identify the types of materials used to make pacemakers and the properties that make these suitable for implanting in the body

Artificial Pacemakers

The artificial pacemaker is an electrical device. Pacemakers are used to stimulate contraction of the heart muscles, in people whose heartbeat is weak or irregular. The pacemaker works by delivering electrical signals (up to 5 volts) into the atrium or ventricle, which then contracts in response. When the hearts own electrical system sends a signal and the heart beats, the pacemaker waits and does nothing. When the heart’s system misses a signal, the pacemaker sends a signal to replace it.

The pacemaker is placed over the ribs, below the right collarbone. It has a pulse generator, which is a small computer that controls the regularity of the electrical pulse being produced and is powered by a special long-life battery. A titanium case protects the generator and battery. A lead connects the pulse generator to the heart. This lead is made of metal covered by soft, plastic, insulating material to ensure that the electrical pulse only goes to the heart muscle. The lead is usually put into a vein below the collarbone and passes to the heart where it is attached to the atrium or ventricle (depending on the condition) by soft plastic hooks or a metal corkscrew. The heart end of the lead has small electrodes made of metal.

Modern pacemakers can be fine-tuned from outside the body using a radio-wave programmer. They need to be checked regularly (about every 6 months) and batteries can be replaced under local anaesthetic. Artificial pacemakers can cope with most normal daily activities and are protected from electrical interference from microwave ovens, televisions and most electrical tools

Notes Questions

25.Where is a pacemaker implanted

26.Sketch a pacemaker. Label the important parts.

Research

a Outline the historical development of pacemakers

b Identify types of technological advances that have made their development possible


Biomaterials and pacemakers

The study and development of artificial body parts occurs within the science of biomedical engineering.

An important property of all biomaterials is that the materials used for will not be rejected by the body’s immune system - that they are biocompatible. The body’s immune system rejects material foreign to it. This mechanism is the same mechanism that fights disease by destroying bacteria.

The environment inside the human body is hot, humid and corrosive. Biomechanical devices and materials must be able to last in such an environment. Properties such as:

Chemical inertness (non-reactive), Resilience (long lasting, non-corrosive), Strength and Flexibility

need to be considered before a material is selected for a biomedical use.

Specific properties, to fulfil the particular requirements needed, must also be considered. Such properties include:

Low friction Electrical conductivity – insulator or conductor

Some problems that occur in relation to biomaterials include: Attachment of the material Swelling Corrosion

There are three basic groups of biomaterials: metals, ceramics and polymers.

Metals Metals that have proven to be biocompatible include titanium, stainless steel, platinum, and cobalt-chromium alloys. Because they are strong, metals are useful in artificial limbs and joint replacements. They are also used in heart valves, dental implants, and electronic devices used to regulate artificial organs.

Ceramics Ceramics can be created with a broad range of properties. Some are very hard. Others make good contact surfaces. Still others are flexible and can be fashioned into artificial tendons and ligaments.

Polymers Polymers are large chainlike molecules that can be custom-made to exhibit a wide range of properties. Two broad types are elastomers and plastics. Elastomers or rubbers are very flexible; if stretched they will return to their original shape. A type of silicone rubber is used to make artificial finger joints; it can be bent 90 million times without breaking. Plastics are rigid. Other polymers commonly used in implants include acrylics, which are used to make artificial eyes and lens implants; Teflon, used for artificial blood vessels; and polyethylene, used on the surface of artificial joints.


Notes Questions

27.Outline what is meant by the term biocompatible.

28. Identify the function of the immune system.

29.Name three properties of biomaterials that allow them to last inside the human body.

30.Name three biocompatible metals.

31.Why are metals useful in artificial limbs?

32.Name three polymers used in bionics

Research

Parts of a pacemaker Generator – a smooth, lightweight case containing a tiny computer and a battery. Connector – the part of the generator where the lead or leads are attached. Leads – wires covered by soft, flexible plastic.

For each of these parts

a. Identify the types of materials used to make pacemakers

b. Identify the properties that make these suitable for implanting in the body


9.3.2 ii Plan and perform an investigation to identify individual aspects that comprise the heart beat

The Heart Beat

A stethoscope can be used to listen to the beat of the heart. Two sounds are generally heard each time the heart beats. The first is a softer, low-pitched “lub”, which lasts a relatively long time. The “lub” sound is really made up of two sounds that merge. One of these represents the vibrations that arise as the muscle fibres of the heart contract. The other is caused by the closing of the tricuspid valve and the bicuspid valve - this is when blood moves from the auricles to the ventricles. The second is a short, high pitched, snapping sound, “dup”. The second sound is made by the snapping-shut of the aortic and pulmonary valves, just as the heart begins to relax. The two sounds occur close together and then there is a slight pause. The sequence would be something like lub,dub---lub,dub---lub,dub---.

The opening and closing of the heart valves cause lub and dub sounds. If a valve is faulty, it may not close tightly when the heart relaxes or open completely when the heart contracts. The passage of blood around the valve causes a sound called a heart murmur. Heart murmurs can also be caused by other conditions. Sometimes they are present in normal hearts.

What to do

Use the information above to plan a first hand investigation to identify individual aspects that comprise the heartbeat

Planning

Information What to doDiscuss the information and questions below. After the discussion plan your investigation.

Is this a first hand investigation?One difficulty with performing a first hand investigation is that listening to the heartbeat requires experience to identify individual aspects. A stethoscope can be used.

Try obtaining an EEG (Electrocardiogram) – with a good description of the important features of the graph.

1. Write-up your investigation using a laboratory report scaffolds.

Heading for the investigation. Aim Risk assessment Equipment needed. Results Conclusion Discussion


9.3.2 iv Construct a simple model to demonstrate the function of valves in the heart

Activity – Demonstrating the function of valves

Surf life saving clubs and other rescue organisations have equipment used for expired air resuscitation. One such device is an air bag oxygen resuscitator – either a Laerdal Air Bag or a CIG Air Bag. Both devices contain valves to make sure the air, flows in one direction only. The diagrams below show examples of these devices.

What to do

1. Use this device to observe the function of valves.

2. Construct your own model to demonstrate the function of valves in the heart.

3. Justify how the valve you constructed is appropriate. [4 marks]

Justify questions are unstructured and usually require an extended answer

In order to answer such a question, you must provide some structure. STEP 1 Identify (& highlight) the important words in the question

STEP 2 Recall definitions of these important words (if necessary) Justify – Support an argument or conclusion

STEP 3 Develop your own answer that reflects the depth required (Verb & marks)


9.3.2 vii Process information to identify different types and functions of artificial valves in the heart

Artificial Valves

Two kinds of prosthetic heart valves are available:

Mechanical valves – created from man-made materials. Lifetime therapy with anticoagulant medication to prevent blood clots on or around the valve is necessary.

Biological (tissue) valves – taken from pig, cow or human donors. Shorter life span but long-term medication often isn’t necessary.

The first artificial valve was implanted in 1952. Early heart valve prostheses were made of a polished CoCr alloy cage surrounding a silicone rubber ball. These valves were sewn into place using a silicone rubber insert underneath a knitted Teflon cloth.

Today there are three main types of artificial mechanical valves. The ball-in-cage valve that looks like a ball inside a hollow cage. The bi-leaf valve that has two flaps that open and close like a pair of swinging doors. The tilting disk valve that has one or two flat or slightly curved disks.

Ball-in-cage (Starr valve)

A Teflon ring is attached to the heart. Then the ball and cage device is placed over it.

Bi-leaf valve

(Gott)

Disk valve


(Hufnagal)


9.3.2.f Describe the problems that can result from faulty valves in the heart

Faulty Heart Valves

Several diseases can damage heart tissue. Listening to the heart using a stethoscope can detect heart problems. If a swishing sound (heart murmur) is heard, then there may be a problem with one or more of the heart valves. The bicuspid valve and the aortic valve are the most common valves to be faulty. The most common cause of heart valve damage is Rheumatic fever in young children (although the incidence of this disease has been greatly reduced in the last 40 years). Valves can also be damaged by other infections or may not be developed properly at birth.

Damaged heart valves can either be too tight or too loose. If they are too tight the valve opening is too small. As a consequence the forward flow of blood is limited. If the valve is too loose it will allow blood to flow backward.

Damaged valves mean that the heart has to work harder to circulate the blood. This can lead to the heart becoming weaker and possibly to heart failure. The heart is no longer able to supply enough oxygen to the tissues of the body. An early sign of damaged valves (heart failure) can be shortness of breath after mild exercise. Later, there is rapid pulse, pains, tiredness and build up of fluid in the body (oedema). This fluid is typically seen as swelling of the legs, especially around the ankles.

Damaged valves can either be repaired by surgery or replaced. Valves will only be replaced if they cannot be repaired. Although replacement of diseased heart valves is a common surgical procedure there is still only limited success with replacement valves in the long term.

There are two major types of artificial valves: tissue or bioprosthetic valves and mechanical (plastic or metal) valves. Bioprosthetic valves include human or animal (pig or cow) valves. These valves are mounted on cloth-covered plastic or metal frames, which make them easier to insert. The problem associated with tissue valves is related to rejection by the body of biological tissue from another organism. Mechanical valves have some advantages because they last longer. However, their disadvantages relate to formation of blood clots around them. Most valves fail due to calcification of the moving components. Medical researchers are working to understand the failure of prosthetic valves so they can develop better designs.


9.3.2 g Describe the properties of materials such as Teflon/pyrolytic carbon that make them versatile materials for making artificial body parts, including heart valves

Polymers

When small molecules are joined together into large molecules a polymer is made. All plastics, fibres and rubber are polymers; so are many naturally occurring substances such as starch, cellulose and proteins. Synthetic polymers have been used in repair and replacement of parts of the human body. There is a wide range and number of polymers used as biomaterials. The ones in current use, have been chosen because there is little body and tissue reactions to the polymer, they are strong yet pliable and are easily synthesised.

Typical uses for polymers as biomaterials include: Polymethylmethacrylate (PMMA): bone cement and contact lenses Polytetrafluorethylene (PTFE): artificial veins Polyurethane: facial prostheses, blood/device interfaces Polyvinychloride (PVC): blood vessels, gastrointestinal grafts, hearing components Polydimethylsiloxane (PDMS): ear and ear parts, heart components including valves and

joints Polyesters: lungs, kidneys, livers, blood vessels Nylons: joints, blood vessels, kidney dialysis Teflon/pyrolytic carbon

Notes Questions

33.When the heart beats it makes two characteristic sounds. What causes these two sounds?

34.What is a heart murmur?

35.Name the two types of artificial valves.

36.Describe how a ball-in-cage valve works. In your description clearly state how the blood flows through the valve.

37.What instrument can be used to detect faulty heart valves?

38.Why do some damaged heart valves limit the flow of blood.

39.Describe how the heart is effected by damaged valves.

40.Name an advantage of mechanical valves over biological valves


9.3.2 h Describe and explain the effects of a build up of plaque on the walls of major arteries and veins on blood flow to and from the heart

Arteriosclerosis

The heart is subject to a great many disorders. Many disorders of the heart are due to the changes brought on by old age. Arteriosclerosis is a major contributor to heart disease. High fat levels in the diet have been identified as a major risk factor in this disease.

Arteriosclerosis is a condition in which the arteries harden. It is due to the build up of fatty deposits on the inside of blood vessels (arteries). These deposits, called plaques, cause cells in the artery walls to break down.

These plaque deposits result in three developments:

1. Substances from the damaged cells irritate nearby tissues, causing scars to form. As a result, the artery wall becomes hard. The artery wall loses elasticity.EFFECT the artery wall cannot expand & therefore blood flow is reduced.

2. This build up roughens the smooth lining of the artery wall.EFFECT rough walls resist blood flow & therefore limits blood flow.

3. The artery wall narrows.EFFECT blood flow reduced.

Because blood flow is reduced the heart has to work harder to pump blood. Eventually, blood flow through the vessels can be severely reduced or blocked altogether.

If atherosclerosis of the coronary arteries occurs then there is reduced circulation of blood and therefore oxygen to the heart muscles. This can lead to either angina (chest pain) or a heart attack.

The rough surface of the wall, together with the sluggish flow of blood through the narrowed channels, may cause a blood clot to form. Clots can block an artery completely. A blocked artery in the brain causes a stroke. Blockage in a coronary artery causes a heart attack.

Almost all heart attacks result from the sudden blockage of a coronary artery. The blockage cuts off the blood supply to part of the heart, and so a portion of the heart dies. Chances of recovery are good if the blockage occurs in one of the smaller coronary arteries. But if one of the larger arteries is blocked, a large part of the heart may be damaged, and the attack is more likely to result in death. Sudden death may also occur from ventricular fibrillation, if the damaged area affects the system that regulates heartbeat.


9.3.2.i Discuss ways in which plaque could be eliminated or altered to ease blood flow

9.3.2 vi Gather information from secondary sources on techniques used, including angioplasty, to ease blood flow to and from the heart and in blood vessels, when there has been a build up of plaque

9.3.2 v Gather, process and analyse information to outline areas of current research in heart transplants and/or artificial hearts and their impact on society


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