1.1 - The cardiovascular system Flashcards
1
Q
What are the 2 parts of the heart divided by?
A
A muscular wall called the septum
2
Q
What are the two chambers in one part of the heart called?
A
Atrium and Ventricle
3
Q
Which are bigger atria or ventricles and why?
A
Ventricles are bigger than atria because the atria only push blood down into the ventricles.
4
Q
Describe the structure of atria and why they are like this.
A
They have thinner walls than the ventricles as pushing blood into the ventricles requires little force.
5
Q
Describe the structure of ventricles and why they are like this.
A
Thick muscular walls as they need to contract with great force to push blood out of the heart.
6
Q
Which side of the heart is thicker/larger and why?
A
The left side is thicker/larger because it needs to pump blood all around the body whereas the right side only pumps deoxygenated blood to the lungs which are in close proximity to the heart.
7
Q
Where does the vena cava take blood? Is it oxygenated or deoxygenated?
A
Deoxygenated blood back to the right atrium.
8
Q
Where does the pulmonary vein take blood? Is it oxygenated or deoxygenated?
A
Oxygenated blood to the left atrium.
9
Q
Where does the pulmonary artery take blood to and from? Is it oxygenated or deoxygenated?
A
Leaves right ventricle with deoxygenated blood to go to the lungs.
10
Q
Where does the aorta take blood to and from? Is it oxygenated or deoxygenated?
A
Leaves left ventricle with oxygenated blood leading to the body.
11
Q
What is the function of valves?
A
Ensure blood only flows in one direction thus preventing back flow. They open to allow blood to pass through before closing again to prevent back flow.
12
Q
Where are the tricuspid, bicuspid and semi-lunar valves located?
A
Tricuspid valve: between the right atrium and right ventricle.
Bicuspid valve: between the left atrium and left ventricle.
Semi-lunar valves: between the right and left ventricles and between the aorta and the pulmonary artery.
13
Q
What is the cardiac conduction system?
A
It is a group of specialised cells located in the wall of the heart which send electrical impulses to the cardiac muscle, causing it to contract.
14
Q
When the heart beats, what needs to happen?
A
The blood needs to flow through the heart in a controlled manner, in through the atria an out through the ventricles.
15
Q
What is the heart muscle described as being and why?
A
Myogenic as the beat starts in the heart muscle itself with an electrical signal in the sinoatrial node (SAN)
16
Q
Where does the heart impulse travel after being started in the sinoatrial node?
A
It spreads through the heart in what is often described as a wave of excitation (similar to a Mexican wave). From the SAN the electrical impulse spreads through the walls of the atria, causing them to contract and forcing blood into the ventricles. It then passes through the atrioventricular node (AVN) found in the atrioventricular septum. The impulse then passes down through some specialised fibres which form the bundles of His.
17
Q
What does the AVN do and what does this allow to happen?
A
Delays the transmission of the cardiac impulse for approximately 0.1 seconds to enable the atria to fully contract before ventricular systole begins.
18
Q
Where is the bundle of His located?
A
It is located in the septum separating the two ventricles. It then branches out into two bundle branches and then moves into smaller bundles called purkinje fibres which spread throughout the ventricles causing them to contract.
19
Q
Define myogenic.
A
The capacity of the heart to generate its own impulses.
20
Q
What is the sinoatrial node (SAN or SA node)?
A
A small mass of cardiac muscle found in the wall of the right atrium that generates the heartbeat. It is more commonly known as the pacemaker.
21
Q
What is systole?
A
When the heart contracts.
22
Q
What is the bundle of His?
A
A collection of heart muscle cells that transmit electrical impulses from the AVN via the bundle branches to the ventricles.
23
Q
What are the purkinje fibres?
A
Muscle fibres that conduct impulses in the walls of the ventricles.
24
Q
How do you remember the conduction system in 6 main points?
A
Sally Always Aims Balls Past Vicky
SAN Atrial systole AVN Bundle of His Purkinje fibres Ventricular systole
25
What is the sympathetic system?
A part of the autonomic nervous system that speeds up heart rate.
26
What is the parasympathetic system?
A part of the autonomic nervous system that decreases heart rate.
27
What is the medulla oblongata?
The most important part of the brain as it regulates processes that keep us alive such as breathing and heart rate.
28
What are chemoreceptors?
Tiny structures in the carotid arteries and aortic arch that detect changes in blood acidity caused by an increase or decrease in the concentration of the carbon dioxide.
29
What are baroreceptors?
Special sensors in tissues in the aortic arch, carotid sinus, heart and pulmonary vessels that respond to changes in blood pressure to either increase or decrease heart rate.
30
What are the 3 main mechanisms which control the rate of which the heart impulses are fired?
Neural control mechanism
Chemoreceptors
Baroreceptors
31
What does the neural control mechanism involve?
The sympathetic nervous system and parasympathetic system stimulating the heart to beat faster and then return to its resting level.
32
What 2 parts make up the nervous system?
The central nervous system (CNS) - The brain and spinal cord.
The peripheral nervous system - Nerve cells included (these transmit information to and from the CNS).
33
What are the CNS and the peripheral nervous system coordinated by?
The cardiac control centre located in the medulla oblongata of the brain. Sympathetic nervous impulses are sent to the SAN and there is a decrease in parasympathetic nerve impulses so that heart rate increases.
34
What is the cardiac control centre stimulated by?
Chemoreceptors
Baroreceptors
Proprioceptors
35
What will happen if there is an increase in carbon dioxide in he blood?
The sympathetic nervous system will be stimulated as the chemoreceptors will detect the increase in carbon dioxide meaning the heart will be faster. This is what happens during exercise.
36
What do baroreceptors contain and what do they do?
nerve endings that respond to the stretching of the arterial wall caused by changes in blood pressure.
37
What do baroreceptors establish?
A set point for blood pressure.
38
Where do baroreceptors send signals to when they detect that the bp has increased or decreased?
The medulla in the brain.
39
What does an increase in the arterial pressure cause?
An increase in the stretch of the baroreceptor sensors resulting in a decrease in HR.
40
What does a decrease in arterial pressure cause?
An decrease in the stretch of the baroreceptor sensors resulting in a increase in HR.
41
What happens to the baroreceptor set point at the start of exercise and why is this important?
The set point increases which is important because the body does not want heart rate to slow down as this would negatively affect performance as less oxygen would be delivered to the working muscles.
42
What are proprioceptors?
Sensory nerve endings in the muscles, tendons and joints that detect changes in muscle movement.
43
What do the proprioceptors detect at the start of exercise?
An increase in muscle movement.
44
Where do proprioceptors send and impulse after detecting an increase in muscle movement at the start of exercise?
They first send an impulse to the medulla, which then sends an impulse through the sympathetic nervous system to the SAN to increase the heart rate. When the parasympathetic system stimulates the SAN, heart rate decreases.
45
What do chemoreceptors detect and what does they do?
Increase in CO2 - creating an increase in HR.
| Decrease in CO2 - creating a decrease in HR.
46
What do baroreceptors detect and what does they do?
Increase in BP - creating a decrease in HR.
| Decrease in BP - creating an increase in HR.
47
What do proprioceptors detect and what does they do?
Increase in muscle movement - creating an increase in HR.
| Decrease in muscle movement - creating an decrease in HR.
48
What is adrenaline?
A stress hormone that is released by the sympathetic nerve and the cardiac nerve during exercise which causes an increase in heart rate.
49
What is stroke volume?
The volume of blood pumped out by the heart ventricles in each contraction.
50
What is the diastole phase?
When the heart relaxes to fill with blood.
51
What is the ejection fraction?
The percentage of blood pumped out by the left ventricle per beat.
52
What does adrenaline stimulate and what does this mean happens?
The SAN (pacemaker) resulting in an increase in both the speed and force of contraction therefore increasing cardiac output. This results in more blood being pumped to the working muscles so they can receive more oxygen for the energy they need.
53
What is the average resting stroke volume?
70ml
54
What 2 things does stroke volume depend upon?
Venous return
| The elasticity of the cardiac fibres
55
What is venous return and how does it affect stroke volume?
The volume of blood returning to the heart via the veins.
If venous return increases, then stroke volume will also increase. (If more blood enters the heart then more will leave!)
56
What is meant by the elasticity of cardiac fibres and how does this affect stroke volume?
It is to do with the degree of stretch of the cardiac tissue during the diastole phase of the cardiac cycle. The more the cardiac fibres stretch, the greater the force of contraction will be. A greater force of contraction can increase the ejection fraction. This is called Starling's law.
57
Summarise into ordered bullet points, Starling's law.
- Increased venous return
- Greater diastolic filling of the heart
- Cardiac muscle stretched
- More force of contraction
- Increased ejection fraction
58
How do you calculate ejection fraction (%)?
Amount of blood pumped out of the ventricle / Total amount of blood in the ventricle
Stroke volume / End diastolic volume (volume of blood in the ventricles at rest)
59
How does the contractility of cardiac tissue (myocardium) affect the force of contraction? And what does this result in?
The greater the contractility of cardiac tissue, the greater the force of contraction. This results in an increase in stroke volume and then an increase in the ejection fraction.
60
What is the average ejection fraction but what can it increase up to following a period of training?
60%
| 85% (following a period of training)
61
Define HR:
The number of times the heart beats per minute
62
What is the average resting HR?
72
63
Define cardiac output:
The volume of blood pumped out by the heart ventricles per minute.
64
How do you calculate cardiac output?
Cardiac output (Q) = Stroke volume (SV) x Heart rate (HR)
65
Using the average values for SV and HR what is the average cardiac output?
```
Q = 70 ml x 72 bpm
Q = 5040 ml (5.04 litres)
```
66
What happens to cardiac output f either stroke volume or heart rate increase?
It increases.
67
What will heart rate increase proportionally to?
Intensity of exercise.
68
How do you calculate Max HR?
220-Age
69
Does a trained performer have a greater or lower heart rate range and why?
A greater range because their resting HR is lower and their maximum HR increases.
70
What is it called when HR increases before exercise and why does this occur?
Anticipatory rise due to hormonal action of adrenaline which causes the SA node to increase the HR.
71
What type of training will result in more cardiac muscle?
Regular aerobic training.
72
What is cardiac hypertrophy?
The thickening of the muscular wall of the heart so it becomes bigger and stronger; also can mean a larger ventricular cavity.
73
What does a stronger heart cause to happen?
Increased SV and therefore an increase in the end diastolic volume of the ventricle increases. If the ventricle can contract with more force and so push out more blood,the heart does not beat as often, so resting heart rate will decrease.
74
What is bradycardia?
A decrease in resting HR to below 60 bpm.
75
What does bradycardia improve and why?
Oxygen delivery to the muscles as there is less oxygen needed for contractions of the heart.
76
What happens to cardiac output, stroke volume and heart rate during exercise?
They all increase.
77
What is the relationship between cardiac output and exercise intensity?
Cardiac output will increase as the intensity of exercise increases until maximum intensity is reached and then it plateaus.
78
Is the cardiac output of a trained and untrained performer the same or different at rest?
It is the same for both.
79
What benefits does an increase cardiac output during exercise have for a trained performer?
Able to transport more blood to the working muscles and therefore more oxygen.
80
What happens in the redistribution of blood when exercise has begun?
When the body starts exercising the distribution of blood changes so a much higher proportion of blood passes to the working muscles and less passes to organs such as the intestine where it is less in demand. The amount of blood passing to the kidneys and brain remains unaltered.
81
What happens to stroke volume in response to exercise?
When does this stop?
Why does this happen?
It increases as exercise intensity increases but this is only the case up to 40-60% of maximum effort. After this point, SV plateaus.
This is because an increased HR near maximum effort results in a shorter diastolic phase. (The ventricles do not have as much time to fill up with blood so they cannot pump as much out).
82
Why/when does Atherosclerosis occur?
Occurs when arteries harden and narrow as they become clogged up by fatty deposits.
83
Define atheroma:
A fatty deposit found in the inner lining of an artery.
84
What is angina?
Chest pain that occurs when the blood supply through the coronary arteries to the muscles of the heart is restricted.
85
What is the leading cause of death in the UK and around the world?
Heart disease or Coronary heart disease (CHD).
86
What causes coronary heart disease?
When the coronary arteries, which supply the heart muscle with oxygenated blood, become blocked or start to narrow by a gradual build-up of fatty deposits.
87
What is the process by which the coronary arteries get blocked and become narrow because of a build-up of fatty deposits known as?
Atherosclerosis.
88
What are some examples of causes of atherosclerosis?
- High blood pressure
- High levels of cholesterol
- Lack of exercise
- Smoking
89
What happens as a result of the arteries becoming narrower?
They become unable to deliver enough oxygen to the heart and pain and discomfort occurs?
90
What is the pain and discomfort in which is caused by a lack of oxygen and blood being supplied to the heart as a result of narrow arteries called?
Angina.
91
What happens if a piece of atheroma breaks off in the coronary artery?
It can cause a blood clot which results in a blockage forming, cutting off the supply of oxygenated blood to the heart muscle resulting in a heart attack.
92
Why is exercise essential in maintaining a healthy heart and blood vessels?
- It keeps the heart healthy and efficient.
- It can pump more blood around the body.
- Makes the heart bigger and stronger.
- Stroke volume increases.
- Maintains flexibility of the blood vessels.
- Ensures good blood flow.
- Maintains normal blood pressure and cholesterol levels.
93
How much exercise is recommend per week and by who? Give an example of moderate exercise:
The American Heart Association recommends at least 150 minutes per week of moderate exercise e.g. Brisk walking.
94
What can high blood pressure cause if it is left untreated?
It puts extra strain on the arteries increasing the risk of heart attack, heart failure, kidney disease, stroke or dementia.
95
What can reduce blood pressure and by how much?
Regular aerobic exercise can reduce both systolic and diastolic pressure by up to 5-10 mmHg reducing the risk of a heart attack by up to 20%.
96
What are the 2 types of cholesterol and what do they do ?
LDL (low density lipoproteins) - Transport cholesterol in the blood to the tissues and are classed as 'bad' cholesterol since they are linked to an increased risk of heart disease.
HDL (high density lipoproteins) - Transport excess cholesterol in the blood back to the liver where it is broken down. These are classed and 'good' cholesterol since they lower the risk of developing heart disease.
97
What can lower bad LDL cholesterol levels and at the same time significantly increase good HDL cholesterol levels?
Regular physical activity.
98
What does the brain need to maintain function?
A constant supply of oxygenated blood and nutrients.
99
When does a stroke occur an what does this cause?
When the blood supply to part of the brain is cut off causing damage to brain cells so they start to die which can lead to brain injury, disability and sometimes death.
100
What are the 2 main types of stroke and how do they occur?
Ischaemic strokes are the most common form and occur when a blood clot stops the blood supply.
Haemorrhagic strokes occur when a weakened blood vessel supplying the brain bursts.
101
How can regular exercise help to lower the risk of a stroke and by how much?
It can lower blood pressure and help to maintain a healthy weight, which can reduce the risk of stroke by 27%.
102
What is 'steady state'?
Where the athlete is able to meet the oxygen demand with the oxygen supply.
103
What should happen during steady state?
The heart rate remains the same.
104
What is cardiovascular drift?
When the heart rate slowly climbs during steady state. It is characterised by a progressive decrease in stroke volume, together with a progressive rise in heart rate.
105
When does cardiovascular drift occur?
During prolonged exercise (after 10 mins), in a warm environment, despite the intensity of the exercise remaining the same.
106
Why does cardiovascular drift occur?
When we sweat, a portion of this lost fluid volume comes from the plasma volume. This decrease in plasma volume will reduce venous return and stroke volume. Heart rate again increases to compensate and maintain a higher cardiac output in an attempt to create more energy to cool the body down.
107
How do you minimise cardiovascular drift?
By maintaining high fluid consumption before and during exercise.
108
Summarise cardiovascular drift and what happens:
- Occurs after a period of exercise
- HR increases
- SV decreases
- Because fluid lost as sweat
- Reduced plasma volume
- Reduced venous return
- Cardiac output increases as more energy needed to cool body down (sweat)
109
What is the vascular system made up of?
5 different blood vessels that carry blood through the body, from the heart, distributing it round the body and then returning it to the heart.
110
What do the blood vessels deliver and what do they help get rid of?
Deliver oxygen and nutrients to the body tissues and take away waste products such as carbon dioxide.
111
What do the blood vessels, heart and lungs ensure during exercise?
That the muscles have an adequate supply of oxygen in order to cope with the increased demand for energy.
112
What are the 2 types of circulation?
Pulmonary - deoxygenated blood from the heart to the lungs and oxygenated blood back to the heart.
Systemic - Oxygenated blood to the body from the heart and deoxygenated blood from the body to the heart.
113
What is the simplified pathway of blood through the vascular system?
```
Heart
Arteries
Arterioles
Capillaries
Venules
Veins
Heart
```
114
Describe the structure of veins:
Thin muscle/elastic tissue layers
Blood is at low pressure
Have valves
Wide lumen
115
Describe the structure of arteries:
Blood at high pressure
Thick elastic outer layer
Small lumen
Smooth inner layer
116
Describe the structure of capillaries:
Only wide enough to allow one RBC to pass through at a time (1 cell thick)
Slows down blood flow
Allows the exchange of nutrients with the tissues to take place by diffusion
117
Define blood pressure:
The force exerted by the blood against the blood vessel wall.
118
Define systolic pressure:
The pressure in the arteries when the ventricles are contracting (forcing blood out of the heart).
119
Define diastolic pressure:
The pressure in the arteries when the ventricles are relaxing (letting blood back into the heart).
120
How do you calculate blood pressure?
blood flow x resistance
121
Where in/on the body is blood pressure measured?
At the brachial artery in the upper arm.
122
What is a typical reading for blood pressure at rest?
120 mmHg / 80 (millimetres of mercury)
123
How does blood pressure vary in the different blood vessels and why?
It is different in the various blood vessels.
It is largely dependent on the distance of the blood vessel from the heart. The low pressure of blood in the veins mean that mechanisms are needed to pump the blood back to the heart (valves).
124
What is venous return?
The return of blood to the right side of the heart via the vena cava.
125
How much of the total volume of blood is contained in the veins at rest and what does this mean?
Up to 70% meaning that a large amount of blood can be returned to the heart when needed.
126
What happens to venous return during exercise and what does this mean?
It increases meaning that if more blood is being pumped back to the heart then more blood has to be pumped out, so SV will increase (Starling's law).
127
What are the three venous return mechanisms?
The skeletal muscle pump - When muscles contract and relax they change shape meaning that the muscles press on the nearby veins and cause a pumping effect and squeeze the blood towards the heart.
The respiratory pump - When muscles contract and relax during breathing in and out, pressure changes occur in the thoracic (chest) and abdominal (stomach) cavities. These pressure changes compress the nearby veins and assist blood return to the heart.
Pocket valves - It is important that blood in the veins only flows in one direction and valves ensure that this happens because once the blood has passed through the valves, they close to prevent the blood flowing back.
128
Apart from the venous return mechanisms, what other factors aid venous return?
- A very thin layer of smooth muscle in the walls of the veins helping to squeeze back towards the heart.
- Gravity helps the blood return to the heart from the upper body.
- The suction pump action of the heart.
129
Why does venous return need to be maintained during exercise?
To ensure the skeletal muscles are receiving enough oxygen to meet the demands of the activity.
130
What is the difference in venous return occurring at rest and during exercise?
At rest, venous return can be efficiently maintained by valves and the smooth muscle found in the veins however, during exercise, because oxygen demand is greater and the heart is beating faster, the vascular system has to help out too (the skeletal muscle pump and respiratory pump).
131
How do you prevent blood pooling after exercise and how does this work?
By doing an active cool-down as the skeletal muscle pump and respiratory pump will continue to work preventing blood from collecting in the veins (blood pooling).
132
What happens to venous return when systolic blood pressure increases?
Venous return increases.
(So when systolic pressure decreases, so does venous return).
133
What is venous return equal to in normal circumstances?
Stroke volume
134
What will happen if venous return increases? (Starling's law).
Heart contracts with more force so ejection fraction increases and therefore the stroke volume will increase.
135
What is venous return determined by?
A pressure gradient.
136
What is the pressure gradient and resistance?
The mean systemic pressure minus the right atrial pressure and resistance is the total peripheral vascular resistance.
(Venous pressure (Pv) - Right atrial pressure (Pra) ) / Venous vascular resistance (Rv).
137
How can venous return be increased?
- Increasing venous pressure (PV)
- Decreasing right atrial pressure (PRA)
- Decreasing venous resistance (RV)
138
How can venous return be decreased?
Increasing right atrial pressure (PRA)
139
What is the blood pressure in the
a) right atrium (PRA)
b) peripheral veins (PV)
normally like and what does this mean for the pressure gradient?
Very low so that the pressure gradient driving venous return from the peripheral veins to the heart is also relatively low. Because of this, just small changes in blood pressure in either the right atrium or the peripheral veins can cause a large change in the pressure gradient and therefore can significantly affect the return of blood to the right atrium.
140
What is plasma?
The fluid part of blood (mainly water) that surrounds blood cells and transports them.
141
What is haemoglobin?
An iron-containing pigment found in red blood cells, which combines with oxygen to form oxyhaemoglobin.
142
What is myoglobin?
Often called 'muscle haemoglobin'. It is an iron-containing muscle pigment in slow-twitch muscle fibres which has a higher affinity for oxygen than haemoglobin. It stores the oxygen in the muscle fibres which can be used quickly when exercise begins.
143
What are mitochondria?
Often referred to as the 'powerhouse' of the cell as aerobic respiration and energy production occur there.
144
What happens to the oxygen in the blood when it diffuses into the capillaries during exercise to supply the skeletal muscles with energy?
3% dissolves into plasma
| 97% combines with haemoglobin to form oxyhaemoglobin.
145
How much oxygen can haemoglobin carry?
When fully saturated, haemoglobin will carry four oxygen molecules. Full saturation occurs when the partial pressure of oxygen in the blood is high. E.g. In the alveolar capillaries of the lungs.
146
What happens to oxygen at the tissues and why?
What is this release of oxygen to the tissues also known as?
At the tissues, oxygen is released from oxyhaemoglobin due to the lower pressure of oxygen that exists there. The release of oxygen from oxyhaemoglobin to the tissues is referred to as the oxyhaemoglobin dissociation.
147
What is the oxyhaemoglobin dissociation curve?
It is a curve which helps us to understand how haemoglobin in our blood transports and releases oxygen. The curve represents the relationship between oxygen and haemoglobin.
148
How much oxygen does haemoglobin give up to the muscles?
23%
149
What is the Bohr shift?
When an increase in blood carbon dioxide and a decrease in pH results in a reduction of the affinity of haemoglobin for oxygen.
150
What is pH?
A measure of acidity. The range goes from 1 to 14 and anything less than 7 indicates acidity.
151
During exercise what happens to the s-shaped curve on the oxyhaemoglobin dissociation curve graph and why?
It shifts to the right because when muscles require more oxygen, the dissociation of oxygen from haemoglobin in the blood capillaries to the muscle tissue occurs more readily. This shift to the right is known as the Bohr shift.
152
What are the 3 factors that are responsible for the increase in the dissociation of oxygen from haemoglobin which results in more oxygen being available for use by the working muscles?
Increase in blood temperature - When blood and muscle temperature increase during exercise, oxygen will dissociate from haemoglobin more readily.
Partial pressure of carbon dioxide increases - As the level of blood carbon dioxide rises during exercise, oxygen will dissociate faster from haemoglobin.
pH - More carbon dioxide will lower the pH in the blood. A drop in blood pH will cause oxygen to dissociate from haemoglobin more quickly (Bohr shift).
153
What is the vascular shunt mechanism?
The redistribution of cardiac output.
154
How/Why is the distribution of blood different at rest compared to during exercise?
During exercise, the skeletal muscles require more oxygen so more blood needs to be redirected to them in order to meet this increase in oxygen demand. This redistribution of blood is known as shunting or the vascular shunt mechanism.
155
In terms of the redistribution of blood, why is it important that a performer doesn't consume food less than an hour before competition?
A full gut would result in more blood being directed to the stomach instead of the working muscles and this would have a negative effect on performance as less oxygen is being made available.
156
Where must blood flow remain constant to during exercise and why?
The brain to ensure that brain function is maintained as the brain needs oxygen for energy.
157
Apart from the skeletal muscles, where else does more blood need to be distributed to during exercise?
The heart because the heart muscle needs oxygen for energy to beat faster and more blood goes to the skin because energy is needed to cool the body down.
158
What are both blood pressure and blood flow controlled by and where is it located?
The vasomotor centre in the medulla oblongata of the brain.
159
During exercise, chemoreceptors will detect chemical changes such as increases in carbon dioxide and lactic acid. What will these receptors then stimulate to cause the redistribution of blood and how?
They will stimulate the vasomotor centre which will redistribute blood flow through vasodilation and vasoconstriction.
160
What is vasodilation?
The widening of the blood vessels to increase the flow of blood into the capillaries.
161
What is vasoconstriction?
The narrowing of the blood vessels to reduce blood flow into the capillaries.
162
During exercise, where will more vasodilation occur?
In the arterioles which are supplying the working muscles with an increased amount of oxygen.
163
During exercise, where will more vasoconstriction occur?
In the arterioles which are supplying non-essential organs such as the intestines and liver with oxygen.
164
Apart from by receptors, what is the redirection of blood flow caused/stimulated by?
Through stimulation of the sympathetic nerves located in the walls of the blood vessel.
165
What happens in terms of blood flow when sympathetic stimulation increases?
Vasoconstriction occurs and blood flow reduces so that it can be redistributed to other parts of the body such as the muscles during exercise.
166
What happens in terms of blood flow when sympathetic stimulation decreases?
Vasodilation occurs and blood flow to that body part increases.
167
What are pre-capillary sphincters and what do they do?
What do they do during exercise?
Tiny rings of muscle located at the opening of capillaries. When they contract, blood flow is restricted through the capillary and when they relax , blood flow is increased.
During exercise, the capillary networks supplying skeletal muscle will have relaxed pre-capillary sphincters to increase blood flow and therefore saturate the tissues with oxygen.
168
Give 4 reasons why redistribution of blood is important:
1. To increase the supply of oxygen to the working muscles.
2. To remove waste products from the muscles, such as carbon dioxide and lactic acid.
3. To ensure more blood goes to the skin during exercise to regulate body temperature and get rid of heat through radiation, evaporation and sweating.
4. To direct more blood to the heart as it is a muscle and requires extra oxygen during exercise.
169
What is arterio-venous difference (A-VO2)?
The difference between the oxygen content of the arterial blood arriving at the muscles and the venous blood leaving the muscles.
170
Describe the arterio-venous difference (A-VO2) at rest:
It is low because not much oxygen is required by the muscles.
171
Describe the arterio-venous difference (A-VO2) during exercise:
It is high as much more oxygen from the blood is needed by the working muscles.
172
Why will an increase in arterio-venous difference (A-VO2) affect gaseous exchange?
Because more oxygen will be taken in and more carbon dioxide will be removed.
173
Does training increase or decrease arterio-venous difference (A-VO2)?
Increase as trained performers can extract a greater amount of oxygen from the blood.
