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Flashcards in Transport in Animals Deck (176):
1

Specialised transport systems are needed due to many reasons, one of which is the high metabolic demands of the organism. Explain what this means.

Metabolic demands are high so diffusion over the long distances is not enough to supply the quantities needed.

2

Specialised transport systems are needed due to many reasons, one of which is the small SA:V ratio of the organism. Explain what this means.

Not only do the diffusion distances get bigger but the amount of surface area available to absorb or remove substances becomes relatively smaller.

3

Specialised transport systems are needed due to many reasons, one of which is the need for particular hormones and enzymes in specific places. Explain what this means.

Molecules such as hormones and enzymes may only be produced in one location in the body but needed in another.

4

Specialised transport systems are needed due to many reasons, one of which is the removal of waste products. Explain what this means.

Waste products of the cells need to be removed from the cell and transported to excretory organs.

5

Name some things transported by the body in specialised circulatory systems.

Oxygen, carbon dioxide, nutrients, waste products and hormones.

6

What are the common features of most circulatory systems?

A liquid transport medium, vessels to carry the medium, a pumping mechanism to move the fluid around the system.

7

What is meant by the term mass transport system?

When substances are transported in a mass of fluid with a mechanism for moving the fluid around the body.

8

True or false? In an open circulatory system, there are very few vessels to contain the transport medium.

True

9

Describe the processes that occur in an open circulatory system.

The transport medium is pumped straight from the heart into the body cavity of the animal. The transport medium is under low pressure. It comes into direct contact with the tissues and the cells. This is where exchange takes place between the transport medium and the cells. the transport medium then returns to the heart through an open-ended vessel.

10

What is the blood in insects called?

Haemolymph

11

What can/can't haemolymph transport?

It doesn't carry oxygen or carbon dioxide. It transports food and nitrogenous waste products and the cells involved in defence against diseases.

12

Describe the structure of the body cavity of an insect including the location of the heart.

The body cavity is split by a membrane and the heart extends along the length of the thorax and the abdomen of the insect

13

True or false? The haemolymph circulates but steep diffusion gradients can't be maintained for efficient diffusion. The amount of haemolymph flowing to a particular tissue cannot be varied to meet changing demands.

True!

14

Where is the blood found in a closed circulatory system?

The blood is enclosed in blood vessels and does not come directly into contact with the cells of the body.

15

In a closed circulatory system, why can the blood travel relatively quickly?

Because the heart pumps the blood around the body under pressure.

16

How do substances leave and enter the blood in a closed circulatory system?

By diffusion through the walls of the blood vessels.

17

In a closed circulatory system, how can the amount of blood flowing to a particular tissue be adjusted?

By widening or narrowing blood vessels.

18

In most closed circulatory systems, how are the respiratory gases carried?

Most closed circulatory systems contain a blood pigment that carries the respiratory gases.

19

Give some examples of where a closed circulatory system can be found.

Echinoderms (sea urchins and starfish), cephalopod molluscs (including the octopods and squid), annelid worms and all of the vertebrate groups.

20

Where does the blood flow in a single closed circulatory system?

Blood flows through the heart and is pumped out to travel all around the body before returning to the heart.

21

Where might a single closed circulatory system be found?

In fish and annelid worms.

22

How many sets of capillaries does the blood pass through in a single closed circulatory system?

It passes through two sets of capillaries before it returns to the heart.

23

What happens to the blood in the two capillaries?

In the first capillary it exchanges oxygen and carbon dioxide. In the second set of capillaries in the different organ systems, substances are exchanged between the blood and the cells

24

Explain why the blood flows back to the heart quite slowly in a single closed circulatory system.

As a result of the blood passing through the two sets of very narrow vessels, the blood pressure in the system drops considerably and so the blood returns to the heart at a much slower rate.

25

Why is a single closed circulatory system not efficient? What effect does this have?

Because on the way back to the heart, the blood travels slower. The activity of animals with single closed circulatory systems tends to be relatively low.

26

True or false? Fish have a relatively efficient single circulatory system which allows them to be very active.

True

27

What feature allows fish to be very active?

They have a countercurrent gaseous exchange mechanism in their gils that allows them to take a lot of oxygen from the water.

28

Give one example of an adaptation fish have other than a counter current mechanism that reduces the metabolic demands on the bodies.

Their body weight is supported by the water in which they live and they also do not maintain their own body temperature.

29

Give some examples of where a double closed circulatory system can be found.

In birds and most mammals

30

True or false? A double closed circulatory system is the most efficient system for transporting substances around the body

True

31

Describe the two circuits the blood travels in a double closed circulatory system.

Blood is pumped from the heart to the lungs to pick up oxygen and unload carbon dioxide, and then returns to the heart. Blood then flows through the heart and is pumped out to travel all around the body before returning to the heart again.

32

In a double closed circulatory system, how many capillary networks does the blood pass through? What does this mean?

The blood passes through one capillary network. This means a relatively high pressure and fast flow of blood can be maintained.

33

What are the three main components of blood vessels?

Elastic fibres, smooth muscle and collagen.

34

Describe the structure and function of elastic fibres.

These are composed of elastin and can stretch and recoil providing the vessel walls with flexibility.

35

Describe the structure and function of smooth muscle.

Contracts or relaxes, which changes the size of the lumen.

36

What is the function of collagen.

Provides structural support to maintain the shape and volume of the vessel

37

What is the function of arteries?

Arteries carry blood away from the heart to the tissues of the body.

38

What do arteries carry? What are the exceptions?

Oxygenated blood except for the pulmonary artery which carries deoxygenated blood from the heart to the lungs and the umbilical artery.

39

Is blood in the arteries under higher or lower pressure than the blood in the veins?

Higher pressure

40

Describe how the elastic fibres in the artery walls help it to perform its function.

Elastic fibres enable them to withstand the force of the blood pumped out of the heart and stretch to take the larger blood volume. In between the contractions of the heart, the elastic fibres recoil which helps to even out the surges of blood pumped from the heart.

41

Why is the lining of an artery (its endothelium) smooth?

To enable the blood to flow easily over it.

42

What is the role of arterioles?

Arterioles link the arteries and the capillaries.

43

How does the structure of an arteriole differ from an artery? Why?

They have more smooth muscle and less elastin. They have little pulse surge but can constrict or dilate to control the flow of blood into individual organs.

44

What is the purpose of smooth muscle in the arteriole? What is the name of these processes?

When the smooth muscle contracts, it constricts the vessel and prevents blood flowing into the capillary bed. It is called vasoconstriction. When the smooth muscle in the wall of an arteriole relaxes, blood flows through into the capillary bed. This is vasodilation.

45

What are capillaries?

Microscopic blood vessels that link the arterioles with the venues and they form an extensive network through all the tissues of the body.

46

Why is the lumen of a capillary small?

SO that red blood cells have to travel through in single file.

47

How are substances exchanged through capillaries?

Substances are exchanged through the capillary walls between the tissue cells and the blood. The gaps between the endothelial cells that make up the capillary walls in most areas of the body are relatively large.

48

Do capillaries carry oxygenated or oxygenated blood?

Blood entering the capillaries from the arterioles is oxygenated. By the time it leaves the capillaries for the venues it has less oxygen and more carbon dioxide.

49

What are the three adaptations of capillaries to their role?

The provide a very large surface area for the diffusion of substances in and out. They have a large cross sectional area than the arterioles so rate of blood flow falls. This allows time for exchange to take place by diffusion. The walls are a single endothelial cell thick so it is a thin layer for diffusion

50

What is the function of veins?

The veins carry blood away from the cells of the body towards the heart.

51

Do veins carry oxygenated or deoxygenated blood? What are the exceptions?

They carry deoxygenated blood except for the pulmonary vein and the umbilical vein.

52

Where does the deoxygenated blood flow after the capillaries?

Into venules then the veins and finally the inferior vena cava.

53

Why do veins not have a pulse?

The surges from the heart pumping are lost as the blood passes through the narrow capillaries.

54

What percentage of your blood is in your veins at any one time?

60%

55

Describe the blood pressure in the veins.

The blood pressure of veins is low compared with the pressure in the arteries.

56

What is the function of veins having valves?

To prevent the back flow of blood.

57

Explain why the blood flows easily through the veins.

The walls contain a lot of collagen and relatively little elastic fibre. The vessels have a wide lumen and a smooth thin lining so the blood flows easily through it.

58

What is the function of venules?

They link the capillaries with veins.

59

What is the structure of venules?

They have very thin walls with just a little smooth muscle. Several venues form a vein.

60

What is one problem with the deoxygenated blood needing to be returned to the heart to be sent to the lungs to become oxygenated again?

The blood is under low pressure and needs to be moved against the force of gravity.

61

Explain what the valves in the veins are and how they work.

They are flaps or infolding of the inner lining of the vein. When blood flows in the direction of the heart, the valves open. If the blood starts flowing backwards, the valves close to prevent back flow.

62

Explain why most of the bigger veins run in the big active muscles.

When the muscles contract, they squeeze the veins and force the blood towards the heart.

63

How does the breathing action help move the blood towards the heart?

The chest acts as a pump. The pressure changes and the squeezing actions move blood in the veins of the chest and abdomen towards the heart.

64

What is the name of the yellow liquid in the blood that carries dissolved glucose and amino acids, mineral ions, hormones and other large proteins?

Plasma

65

What is the role of albumin in the body?

It is important for maintaining the osmotic potential of the blood

66

What is the role of fibrinogen in the body?

It is important for blood clotting.

67

What are globulins involved in?

They are involved in transport and the immune system

68

What is the main role of red blood cells?

They carry oxygen to the cells.

69

What are platelets? Where do they come from? What do they do?

Platelets are fragments of large cells called megakaryocytes found in the red bone marrow and are involved in the clotting mechanism of the blood.

70

What percentage of blood by volume does plasma make up?

55%

71

Name the four components of the blood.

Plasma, erythrocytes, platelets, leucocytes.

72

What are the seven things that the blood transports?

Oxygen to and carbon dioxide from the respiring cells, digested food from the small intestine, nitrogenous waste products, hormones, food molecules, cells and antibodies involved in the immune response.

73

True or false? The blood also contributes to maintenance of a steady body temperature and acts as a buffer, minimising pH changes.

True.

74

What is the name given to the tendency of water to move into the blood by osmosis? What is its value?

Oncotic pressure and it is about -3.3kPa

75

Describe the osmotic effect of the plasma proteins in the capillaries.

The plasma proteins give the blood in the capillaries a relatively low water potential compared with the surrounding fluid. Therefore water moves into the blood in the capillaries from the surrounding fluid by osmosis.

76

What is hydrostatic pressure?

The pressure of the blood from the surge of blood that occurs overtime the heart contracts.

77

Describe how hydrostatic pressure affects osmosis in the arteriole end of the capillaries.

At the arteriole end of the capillary, the hydrostatic pressure forcing the fluid out of the capillaries is relatively high. It is higher than the oncotic pressure so fluid moves out of the capillaries.

78

What is tissue fluid?

The fluid that fills the spaces between the cells.

79

What is the composition of tissue fluid?

It has the same composition as the plasma without the red blood cells and the plasma proteins.

80

Describe how hydrostatic pressure affects osmosis in the venous end of the capillaries.

The hydrostatic pressure is lower in the vessels because the fluid has moved out and the pulse is completely lost. Te oncotic pressure is greater than the hydrostatic pressure so water moves back into the capillaries by osmosis.

81

What is lymph?

The liquid that does not return to the capillaries. It leaves trebled vessels and drains into a system of blind-ended tubes called lymph capillaries.

82

What is the composition of lymph?

Lymph is similar in composition to plasma and tissue fluid but has less oxygen and fewer nutrients. It also contains fatty acids.

83

How does lymph move?

The lymph capillaries join up to form larger vessels. The fluid is transported through them by the squeezing of the body muscles. One way valves like those in the veins prevent the backflow. Eventually the lymph returns to the blood flowing into the right and left subclavian veins.

84

What happens in the lymph nodes?

Lymphocytes build up in the lymph node when necessary and produce antibodies which are then passed in to the blood. Lymph nodes also intercept bacteria and other debris which are ingested by phagocytes in the nodes.

85

Why do doctors often examine the neck, armpits, stomach or groin of their patients?

These are the sites of some of the major lymph nodes. Enlarged lymph nodes are a sign that the body is fighting off an invading pathogen.

86

Describe one adaptation that erythrocytes have that helps with their main function of transporting oxygen.

Erythrocytes have a biconcave shape. This shape has an increased surface area available for diffusion of gases. It also helps them to pass through narrow capillaries.

87

In adults, where are erythrocytes formed?

Continuously in the red bone marrow.

88

What is the benefit of erythrocytes not having a nucleus?

It maximises the amount of haemoglobin that fits into the cells.

89

What is the lifespan of erythrocytes in the blood stream?

120 days.

90

True or false? It is the haemoglobin that gives the erythrocytes their red colour.

True

91

Describe the structure of haemoglobin.

Haemoglobin is made up of four polypeptide chains each with an iron-containing harm prosthetic group.

92

How many oxygen molecules can each haemoglobin molecule bind to?

Each haemoglobin molecule can bind to four oxygen molecules.

93

When the oxygen binds to haemoglobin, what is it known as?

Oxyhaemoglobin

94

What is the equation for the reversible reaction of the formation of oxyhaemoglobin?

Hb + 4O2 ---> Hb(O2)4

95

Describe the concentration gradient that allows the erythrocytes to carry oxygen.

When the erythrocytes enter the capillaries in the lungs, the oxygen levels in the cells are relatively low. This makes a steep concentration gradient between the inside of the erythrocytes and the air in the alveoli. Oxygen moves into the erythrocytes and binds with the haemoglobin.

96

What does the arrangement of the haemoglobin molecule allow? What is this called?

As one molecule of oxygen binds to a haem group, the molecule changes shape, making it easier for the next oxygen molecule to bind. This is called positive cooperativity.

97

How can a steep diffusion gradient for oxygen be maintained?

The oxygen is bound to the haemoglobin so the free oxygen concentration in the erythrocyte stays low. A steep diffusion gradient is maintained until all f the haemoglobin is saturated with oxygen.

98

What happens once the blood reaches the body tissues?

The concentration of oxygen in the cytoplasm of the body cells is lower than in the erythrocytes. As a result, oxygen moves out of the erythrocytes down a concentration gradient.

99

What happens after the first oxygen molecule is released by the haemoglobin?

The molecule changes shape and it becomes easier to remove the remaining oxygen molecules.

100

What is the purpose of an oxygen dissociation curve? What two pieces of information are plotted?

These show the affinity of haemoglobin for oxygen. The percentage saturation haemoglobin in the blood is plotted against the partial pressure of oxygen.

101

True or false? A very small change in the partial pressure of oxygen in the surroundings makes a significant difference to the saturation of the haemoglobin with oxygen.

True

102

Why does it only take a very small change in the partial pressure of oxygen in the surroundings makes a significant difference to the saturation of the haemoglobin with oxygen?

Once the first molecule becomes attached , the change in shape of the haemoglobin molecule means other oxygen molecules are added rapidly.

103

Why does the curve level out at the highest partial pressures of oxygen?

Because all the haem groups are bound to oxygen and so the haemoglobin is saturated and cannot take up any more.

104

What happens at high partial pressures of oxygen in the lungs?

The haemoglobin in the red blood cells is rapidly loaded with oxygen.

105

What percentage of oxygen carried in your erythrocytes is released into the body cells? What does the rest act as?

25%, the rest acts as a reservoir for when the demands of the body increase suddenly.

106

What is the Bohr effect?

As the partial pressure of carbon dioxide rises (at higher partial pressures of CO2) haemoglobin gives up oxygen more easily.

107

The Bohr effect is important in the body because as a result....

In active tissues with a high partial pressure of carbon dioxide, haemoglobin gives up its oxygen more readily.
In the lungs where the proportion of carbon dioxide in the air is relatively low, oxygen binds to the haemoglobin molecules easily.

108

Describe how a developing fetus receives oxygenated blood.

Oxygenated blood from the mother runs close to the deoxygenated blood in the placenta.

109

Why can't the blood of the fetus have the same affinity for oxygen as the blood of the mother?

If the blood of the foetus had the same affinity for oxygen as the blood of the mother, then very little or no oxygen would be transferred to the blood of the fetus.

110

Why can fetal haemoglobin remove oxygen from the maternal blood as they move past each other?

Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin at each point along the dissociation curve.

111

What are the three different ways that carbon dioxide is transported from the tissues to the lungs?

It is carried dissolved in the plasma, combined with the amino groups in the polypeptide chains of haemoglobin and the rest is converted into hydrogen carbonate ions in the cytoplasm of the red blood cells.

112

What is the name of the product formed when carbon dioxide combines with the amino groups in the polypeptide chains of haemoglobin?

Carbaminohaemoglobin.

113

How is most of the carbon dioxide that diffuses into the lungs transported?

In the form of hydrogen carbonate ions.

114

How are hydrogen carbonate ions formed?

Carbon dioxide reacts slowly with water to form carbonic acid (H2CO3-). The carbonic acid then dissociates to form hydrogen ions and hydrogen carbonate ions.

115

What is the role of carbonic anhydrase?

This enzyme catalyses the reversible reaction between carbon dioxide and water to form carbonic acid. This helps it to take place faster than in the blood plasma.

116

How do the negatively charged carbonate ions move out of the erythrocytes into the plasma?

The negatively charged carbonate ions move out of the erythrocytes into the plasma by diffusion down a concentration gradient and negatively charged chloride ions move into the erythrocytes which maintains the electrical balance of the cell.

117

What is the chloride shift?

When negatively charged chloride ions move into the erythrocytes in order to maintain the electrical balance of the cell.

118

What effect does removing the carbon dioxide and converting it to hydrogen carbonate ions have?

The erythrocytes maintain a steep concentration gradient for carbon dioxide to diffuse from the respiring tissues in to the erythrocytes

119

What happens when the blood reaches the lung tissue where there is a relatively low concentration of carbon dioxide?

Carbonic anhydrase catalyses the reverse reaction, breaking down carbonic acid into carbon dioxide and water.

120

What happens at the lung tissue to the hydrogen carbonate ions?

They diffuse back in to the erythrocytes and react with hydrogen ions to form more carbonic acid. When this is broken down by carbonic anhydrase it releases free carbon dioxide which diffuses out of the blood into the lungs.

121

What happens to the chloride ions at the lung tissue?

They diffuse out of the red blood cells back into the plasma down an electrochemical gradient.

122

What is the role of haemoglobin in the diffusion of chloride ions out of the red blood cells?

It acts as a buffer and prevents changes in the pH by accepting free hydrogen ions in a reversible reaction to form haemoglobin acid.

123

Which part of the heart does deoxygenated blood flow to?

Deoxygenated blood from the body flows in to the right side of the heart, which pumps it into the lungs.

124

Which part of the heart does oxygenated blood flow to?

Oxygenated blood from the lungs returns to the left side of the heart which pumps it to the body

125

Does the blood from the two sides of the heart ever mix?

No, the oxygenated and deoxygenated blood never mix.

126

What type of muscle is the heart made from? Why?

The heart is made of cardiac muscle which contracts and relaxes in a regular rhythm. It doesn't get fatigued or need to rest like skeletal muscle.

127

Which artery supplies the cardiac muscle with the oxygenated blood it needs to keep contracting and relaxing?

The coronary artery

128

What is the function of the heart being surrounded by inelastic pericardial membranes?

It helps to prevent the heart from over-distending with blood.

129

Which wall of the heart is very thick?

The left ventricle wall

130

As you look at the diagram of the heart, where would you find the left ventricle?

On the right hand side of the picture at the bottom.

131

As you look at the diagram of the heart, where would you find the left atrium?

On the right hand side of the picture near the top.

132

As you look at the diagram of the heart, where would you find the right ventricle?

On the left hand side of the picture at the bottom.

133

As you look at the diagram of the heart, where would you find the left atrium?

On the left hand side of the picture near the top.

134

As you look at the diagram of the heart, where would you find the tricuspid valve?

On the left hand side of the picture between the right atria and the right ventricle.

135

As you look at the diagram of the heart, where would you find the bicuspid valve?

On the right hand side of the picture between the left atria and the left ventricle.

136

As you look at a diagram of the heart, where would you find the semilunar valves?

Between the right ventricle and left pulmonary artery.

137

When looking at a diagram of the heart, on which side would you find the pulmonary veins?

On the right side.

138

What is the name of the arteries that come off the aorta?

The carotid arteries

139

As you look at the diagram of the heart, where would you find the superior vena cava?

On the left hand side of the diagram, at the top.

140

As you look at the diagram of the heart, where would you find the inferior vena cava?

On the left hand side of the diagram, at the bottom

141

Give one feature of the heart that allows you to distinguish which side is the right and which side is the left.

The apex. A 'point' that always goes on the right hand side of a diagram to show the left ventricle.

142

Where does the blood come from when it enters the superior and inferior vena cava, where does it go to and what pressure is it at?

Deoxygenated blood from the upper body and head enters in the superior vena cava and deoxygenated blood from the lower body enters in the inferior vena cava. The blood goes to the right atria under low pressure.

143

Describe what happens as the blood flows into the atria and then into the right ventricle?

The atria have thin walls. As the blood flows in, a pressure builds until the tricuspid valve opens. Blood moves into the right ventricle. When the ventricle has filled with blood, the atrium contracts which forces the remaining blood out of the atrium which stretches the ventricle walls. The tricuspid valve closes to prevent backflow.

144

What is the purpose of the tendinous cords in the heart?

The tendinous cords make sure that the valves are not turned inside out by the pressures exerted when the ventricle contracts.

145

What happens to the blood once it has reached the right ventricle?

The right ventricle contracts fully and pumps deoxygenated blood through the semilunar valves into the pulmonary artery, which transports it to the capillary bed of the lungs

146

What is the role of the semilunar valves?

To prevent the backflow of blood.

147

What happens to the oxygenated blood as the deoxygenated blood is being pumped to the pulmonary artery?

Oxygenated blood from the lungs enters the left atrium from the pulmonary vein. Pressure in the atrium builds and the bicuspid valve opens so the oxygenated blood enters the left ventricle. The atrium contracts which forces the remaining blood into the left ventricle. The left ventricle then contracts and pumps oxygenated blood through semilunar valves into the aorta. As the ventricle contracts the tricuspid valve closes.

148

Explain why the muscular wall of the left side of the heart is much thicker than that of the right.

The lungs are relatively close to the heart so the right side of the heart has to pump the blood a relatively short distance and only has to overcome the resistance of the pulmonary circulation. The left side has to produce sufficient force to overcome the aorta and move the blood under pressure to all the extremities of the body.

149

What is the septum and what is its purpose?

The septum is the inner dividing wall of the heart which prevents the mixing of deoxygenated and oxygenated blood.

150

True or false? The right and left side of the heart fill and empty together.

True

151

What is the cardiac cycle?

The cardiac cycle describes the events in a single heartbeat, which lasts about 0.8 seconds in a human adult.

152

What happens in diastole?

The heart relaxes. The atria and then the ventricles fill with blood. The volume and pressure of the blood in the heart builds but the pressure in the arteries is at a minimum.

153

What happens in systole?

The atria contract (atrial systole) closely followed by the ventricles (ventricular systole). The pressure inside the heart increases dramatically and blood is forced out of the right side of the heart to the lungs and from the left side to the main body circulation. The volume and pressure the blood in the heart are low and the blood pressure in the arteries is at a maximum.

154

Describe what causes the 'lub-dub' of the heartbeat.

The first sound comes as the blood is forced against the atria-ventricular valves as the ventricles contract and the second sound comes as a black flow of blood closes the semilunar valves in the aorta and pulmonary artery as the ventricles relax.

155

Cardiac muscle can be described as myogenic. What does this mean? Why is this beneficial?

I has its own intrinsic rhythm. This prevents the body wasting resources maintaining the basic heart rate.

156

What is the average resting heart rate of an adult? Why is it an average?

70bpm, it is an average because other factors including exercise, excitement, and stress also affect our heart rate.

157

What is the basic rhythm of the heart maintained by?

A wave of electrical excitation rather like a nerve impulse

158

Where does the wave of electrical excitation begin? What happens?

A wave of electrical excitation begins in the sino-atrial (SAN) causing the atria to contract and so initiating the heartbeat.

159

What prevents the excitation passing directly to the ventricles?

A layer of non-conducting tissue.

160

What happens after the electrical activity of the SAN?

The activity is picked up by the atria-ventricular node (AVN). It imposes a slight delay before stimulating the bundle of His.

161

What is the bundle of His?

A bundle of conducting tissue made up of fibres (Purkyne fibres) which penetrate through the septum between the ventricles

162

How does the bundle of His spread the excitation?

It splits into two branches and conducts the wave of excitation to the apex of the heart.

163

What happens to the electrical excitation at the apex?

The Purkyne fibres spread out through the walls of the ventricles on both sides. The spread of excitation triggers the contraction of the ventricles, starting at the apex.

164

Why does contraction of the ventricles start at the apex?

It makes it more efficient at emptying the ventricles.

165

Why is there a delay between the way in which the wave of excitation spreads through the heart from the SAN to the AVN?

To make sure that the atria have stopped contracting before the ventricles start.

166

What is an electrocardiogram?

A measure of the spread of electrical excitation through the heart.

167

What EXACTLY does an ECG measure?

The tiny electrical differences in your skin, which result from the electrical activity of the heart.

168

What is an ECG used for?

To help to diagnose heart problems.

169

What is tachycardia?

When the heartbeat is very rapid, over 100bpm.

170

When is tachycardia normal? If it is abnormal what is it caused by?

It is normal when you exercise, if you have a fever or if you are frightened/angry. If it is abnormal it may be caused by problems in the electrical control of the heart and may need to be treated with medication or surgery.

171

What is bradycardia?

When the heart rate slows down to below 60bpm.

172

Why do many people have bradycardia? What can be done to treat severe bradycardia?

Many people have it because they are fit- training makes the heart beat more slowly and efficiently. Severe bradycardia may need to be treated with an artificial pacemaker.

173

What is an ectopic heartbeat?

Extra heartbeats that are out of the normal rhythm.

174

Are ectopic heartbeats normal?

Most people have at least one a day. They are usually normal but they can be linked to serious conditions if very frequent.

175

What is atrial fibrillation?

An example of an arrhythmia which is an abnormal rhythm of the heart.

176

Explain what causes atrial fibrillation.

Rapid electrical impulses are generated in the atria. They contract very fast up to 400 times a minute. However they don't contract properly and only some of the impulses are passed on to the ventricles, which contract much less often. As a result the heart does not pump blood very effectively.