Cardiac Physiology Flashcards
(152 cards)
1
Q
Define the term “artery”
A
vessels taking the blood away from the heart
2
Q
Define the term “arteriole”
A
The branching vessels coming off arteries that are responsible for controlling the blood flow to the different systems of the body.
3
Q
In which vessels does gas exchange occur?
A
Capillaries
4
Q
In which vessels is a large volume of blood stored?
A
Venules and veins
5
Q
How much of the body blood supply is held in venues and veins at any one time?
A
2/3
6
Q
Explain how to left and right sides of the heart remain in series
A
They pump equal amounts of blood
7
Q
Are most vascular beds arranged in parallel or in series?
A
In parallel
8
Q
Other than the left and right sides of the heart, which other vascular beds are arranged in series?
A
gut & liver
9
Q
Why are the gut and the liver in series?
A
lots of nutrients are picked up in the gut and they are passed on to the liver
10
Q
What is the name of the specialised blood supply that supplies the liver?
A
The portal circulation
11
Q
What is the total % oxygen consumption of the brain? (Remember the flow at rest is 5L/min)
A
18%
12
Q
What is the total % oxygen consumption of the heart? (Remember the flow at rest is 5L/min)
A
10%
13
Q
What is the total % oxygen consumption of the skeletal muscle? (Remember the flow at rest is 5L/min)
A
20%
14
Q
What is the total % oxygen consumption of the skin? (Remember the flow at rest is 5L/min)
A
2%
15
Q
What is the total % oxygen consumption of the kidney? (Remember the flow at rest is 5L/min)
A
6%
16
Q
What is the total % oxygen consumption of the abdominal organs? (Remember the flow at rest is 5L/min)
A
30%
17
Q
The kidneys are sent a huge amount of blood however the total oxygen consumption is low- explain this discretion
A
- The kidneys are sent such a high quantity of blood for filtration, not due to the energy demand, hence the discretion between the amount of blood they receive (Flow at Rest ml/min) and the total oxygen consumption.
18
Q
What makes the redirecting of blood possible?
A
The relaxation and contraction of the arterioles
19
Q
How is blood flow calculated?
A
(Mean arterial pressure-central venous pressure) divided by (resistance - radius to the power of 4)
20
Q
Why is the elasticity of the aorta so important?
A
Elasticity allows it to absorb some of the pressure exerted upon it during the ejection phase (the walls are able to bulge outwards). This absorbed pressure can then be used to help push the blood through the aorta during the heart’s relaxation phase
21
Q
Is the aortic lumen large or narrow?
A
Large
22
Q
Describe the lumen and the wall of muscular arteries
A
wide lumen and a strong, thick non-elastic wall
23
Q
Why are muscular arteries not elasticated?
A
By lacking elastic tissue, they allow the blood to reach the peripheries of the body without a drop in pressure
24
Q
What type of blood vessel is a resistance vessel?
A
Arterioles
25
What makes arterioles resistance vessels?
They have a narrow lumen, a thick muscular awl and the ability to relax and contract
26
What makes capillaries ideal for diffusion?
They are only one cell thick and therefore have a large surface to volume ratio
27
What enables venules and veins to store large volumes of blood?
A wide lumen and a dispensable (collapsible) wall. This allows them to retain and store a large volume of blood in cases of pressure increase.
28
What are the two main functions of venules and veins?
To move blood back to the heart and to store blood
29
Why are venules and veins referred to as capacitance vessels?
because of how much blood they can store
30
What is fractional distribution?
The amount of blood stored in the capacitance vessels Vs how much blood is circulating in the rest of the vessels.
31
Are venules and veins high or low resistance?
Low
32
What separates the two half of the heart?
Septum
33
What is the heart wall made from?
Muscle (myocardium)
34
The left side of the heart pumps blood out into the systemic circulation through the ________
Aorta
35
Deoxygenated blood returns to the right side of the heart via the _______ ____ ______ _______ _______
superior and inferior vena cava
36
Deoxygenated blood entering the right atrium will travel through to the right ventricle and will then enter the ______ ______ which splits into the _____ and ______ _______ ________ which takes blood to the left and right lungs.
Deoxygenated blood entering the right atrium will travel through to the right ventricle and will then enter the pulmonary artery which splits into the left and right pulmonary artery which takes blood to the left and right lungs.
37
Oxygenated blood from the lungs returns to the right atrium of the heart through the ___________ _______
Pulmonary veins
38
Do the heart valves require entry to function?
No- they are passive!
39
The _____ valve lies at the entrance to the left
Aortic
40
The left atrium and the left ventricle are separated by the _________ valve
Mitral
41
At the entrance to the right atrium is the ____________ valve
Pulmonary
42
The right atrium and right ventricle are separated by the ________ valve
Tricuspid
43
Which is the only valve with three flaps?
Tricuspid
44
Which valves are associated with cordae tendinae?
Mitral and tricuspid
45
What is the function of the cordae tendinae?
prevent the mitral and tricuspid valves from turning inside out and allowing blood to regurgitate due to the pressure inside the heart.
46
When does the cordae tendinae contract?
At the same time as the heart
47
What are the three biggest differences between cardiac and skeletal muscle?
1. Cardiac cells have an intercalated disk made up of a gap junction and a desmosome (this allows cardiac cells to depolarise one another)
2. The action potential in cardiac muscle is much longer than it is in skeletal muscle (250ms vs 2ms in skeletal).
3. Some cardiac cells have an unstable resting membrane potential which allows them to act as pacemakers
48
Why is the cardiac action potential much loner than the skeletal muscle action potential?
When the voltage gated channels open to depolarise the cell, calcium AND Sodium enter the cardiac cell (in skeletal muscle, only sodium enters the cell).
49
What is responsible for the autorhythmic nature of the heart
The pacemaker cells
50
Where are the fastest pacemaker cells located?
The SA node
51
At what speed does the wave of depolarisation move across the atria?
0.5 metres/ second (fairly slowly)
52
Name the only bit of the heart made from non-conducting tissue
The annulus fibrosis
53
Where is the annulus fibrosis located?
between the atria and ventricles
54
What is the function of the annulus fibrosis?
Ensures that the depolarisation is directed through the AV node
55
At what speed does the wave of depolarisation move through the AV node?
0.05m/second
56
After moving through the AV node, where does the electrical signal go to next?
down into the bundle of His which then splits up into the Purkinje fibres
57
At what speed does the wave of depolarisation move through the purkinje fibres?
5 metres/second
58
What causes the P wave on an ECG?
The wave of depolarisation moving across the atria
59
What causes the QRS complex?
the wave of depolarisation moving across the ventricles
60
What causes the T wave?
the repolarisation of the ventricles
61
How many seconds is one large square on the ECG paper equivalent to?
0.2 seconds
62
What is heart block?
when the depolarisation from the atrium doesn’t reach the ventricles due to a problem with the atrioventricular node
63
What is first degree heart block and how does it look on an ECG?
a PQRST progression that looks normal except there is a long delay between the P wave and the QRS complex (normal the interval between the P wave and the start of the QRS complex should be less than 0.18 seconds).
64
What is second degree heart block and what does it look like on an ECG?
some of the depolarisations don’t get through at all. This will be demonstrated by a longer and longer delay between the P wave and the QRS complex across the ECG paper followed by a P wave with no subsequent QRS complex
65
What is a third degree heart block?
there is no transmission between the atria and the ventricles. To replace the depolarisation that is not making it through the AV node, pacemaker cells in the ventricle will cause a ventricular contraction. The ECG therefore has no coordination between the P wave and the QRS complex. The heart rate in patients with a 3rd degree heart block will be slow.
66
Which stage of the cardiac cycle is the filling stage?
Diastole
67
do the atria fill with blood actively or passively during diastole?
Passively
68
What happens during isometric contraction?
the ventricles start to contract but they don’t get any shorter, as this happens, the increase in pressure pushes the mitral valve and tricuspid valve closed.
69
When do the pulmonary and aortic valves open?
When the pressure inside the ventricles is high enough to push them open q
70
When do the pulmonary and aortic valves close?
At the point where the pressure inside the ventricles becomes less than the pressure inside the arteries
71
When does isometric relaxation occur?
From the point where the ventricles contract and eject blood into the vessels to the point where the pressure inside the ventricles is below the pressure inside the atria.
72
When do the mitral and tricuspid valves open?
When the pressure inside the ventricles is below the pressure inside the atria.
73
What fraction of the cardiac cycle is taken up by systole and diastole respectively?
Systole takes up about 1/3 of the cycle and diastole (the filling phase) takes up about 2/3 of the cycle at rest
74
What is the pressure inside the aorta at the point where the mitral valve is open?
the pressure inside the aorta follows the pressure inside the ventricle (because the two are connected).
75
What happens to the pressure inside the aorta as the ventricles begin to relax?
It begins to drop
76
What causes the aortic valve to close?
The elastic energy of the aorta pushes the column of blood and pushes a bit of it backwards this pushes the aortic valve shut.
77
Why is the drop in pressure inside the aorta slower than the drop in pressure inside the ventricles?
The drop in pressure in the aorta is much slower due to the elastic energy which can continue to push down on the column of blood even as the ventricular pressure falls.
78
What is the diastolic pressure?
the minimum pressure inside the aorta
79
What is the average diastolic pressure of a healthy individual?
80mmHg
80
What is the pulse pressure difference and how is it calculated?
the difference between the systolic and diastolic blood pressure. (120-80= 40mmHg on average)
81
Why is the mean arterial pressure not half way between the systolic and diastolic reading?
Because the heart spends more time in diastole than it does in systole
82
How do you calculate the mean arterial pressure?
diastolic pressure + 1/3rd of the systolic pressure
83
What is the "end diastolic volume"?
The peak volume of blood in the ventricle at the end of the filling phase
84
What is the end systolic volume?
The minimum volume of blood left in the ventricles at the end of the ejection phase
85
What is the average end diastolic volume in a healthy individual?
140ml
86
What is the average end systolic volume?
60ml
87
Is the heart completely emptied of blood at the end of systole?
No- some blood is not pumped out (this is the end systolic volume)
88
What is the stroke volume?
The volume of blood that is pumped out with each heartbeat
89
How is the stroke volume calculated?
(End diastolic volume) - (end systolic volume)
90
What is the most significant factor influencing the volumes of blood processed by the heart?
Size
91
What is the ejection fraction?
the stroke volume expressed as a fraction of the end diastolic volume.
92
How is the ejection fraction calculated?
stroke volume/ end diastolic volume
93
What is the standard ejection fraction of a healthy heart?
2/3
94
What are abnormal heart sounds referred to as?
Murmurs
95
What causes murmurs?
A natural narrowing of the valve called stenosis
Improper closure of the valves causing the regurgitation of blood back into the atria/ventricle (depending on which valve it is).
96
When would a systolic murmur be heard?
Between the lab and the dub (Lub murmur dub)
97
When would a diastolic murmur be heard?
After the lab dub (dub dub murmur)
98
What would be the cause of a murmur that is heard throughout the cardiac cycle?
A hole in the heart septum
99
Which direction would blood move through a hole in the septum?
Left to right (because pressure is higher on the left side)
100
What can alter the rate at which pacemaker cells in the sinoatrial node depolarise?
sympathetic and parasympathetic nervous systems.
101
What effect does the sympathetic nervous system have on heart rate?
It increases the heart rate
102
How does the sympathetic nervous system increase heart rate?
Sympathetic nerves release noradrenaline which acts on beta 1 receptors in the SA nod. When the beta 1 receptors are stimulated they increase the heart rate by modulating leaky potassium channels, T-type sodium channels and normal sodium channels which allows pacemaker cells to reach threshold sooner
103
Explain how the parasympathetic nervous system slows the heart rate
The vagus nerve releases acetylcholine which acts on muscarinic receptors in the sinoatrial node. This causes the cells to hyper polarise, taking them further from threshold and increasing the time taken for cells to depolarise and fire an action potential
104
What are the three different things that can influence stroke volume (how strongly the heart beats)
1. Preload (intrinsic factor)
2. Afterload (intrinsic factor)
3. Sympathetic nervous system (increases contractility and strength of contraction)
105
What is preload?
The length of a muscle fibre before it is stimulated to contract
106
Explain why end diastolic pressure is important in stroke volume
If end diastolic pressure is high, it will increase the preload (because the higher volume of blood will cause the heart muscle to stretch more) and this will subsequently increase the stroke volume (remember stroke volume is the amount of blood that is pumped out with each heartbeat).
If end diastolic pressure is low, the preload will be less (because the muscle will not stretch as much) and the stroke volume therefore will be less
107
What is afterload?
is the forces against which the muscle tries to contract
108
What is total peripheral resistance?
a measure of how easy it is for blood to move out of the aorta and into the arterioles
109
Why does an increase in afterload cause a decrease in stroke volume?
If the total peripheral pressure is high, the pressure in the aorta will also be higher. This means that the heart will have to build up more pressure in order to open the aortic valve and push the blood out and will therefore have to spend more time in the isometric contraction phase in order to build up enough energy to open the aortic valve. This means that less energy will be left to actively eject the blood from the heart and therefore stroke volume will be decreased.
110
Explain how the sympathetic and parasympathetic nervous systems can affect stroke volume
Sympathetic nerves release noradrenaline which acts on beta 1 receptor in the myocardium and increases the contractility of the myocytes giving stronger, yet shorter contractions.
The parasympathetic nervous system has very little control over stroke volume. This is probably because the vagus nerve does not innervate the ventricular muscle
111
How is cardiac output calculated?
Heart rate x stroke volume
112
What is a normal arterial blood pressure?
120/80mmHg
113
Why does blood pressure rise with gas?
Due to a loss of elasticity in blood vessels
114
Why does blood pressure drop significantly as it moves from arteries into arterioles?
because arterioles are resistance vessels
115
What is systemic filling pressure?
The small difference in pressure between the veins and the right atrium which helps to push blood through the veins and back to the heart
116
What does the term "velocity" refer to?
The speed of an individual blood cell
117
Where in the circulatory system is velocity highest and lowest
Highest in aorta and vena cava
Lowest in the capillaries
118
List 5 factors that affect pressure and flow in veins
```
– gravity
– skeletal muscle pump
– respiratory pump
– venomotor tone
– systemic filling pressure
```
119
What impact does gravity have on venules and veins?
when standing, the pressure inside the venules in the leg will be greater than the pressure inside the venules of the head as a result of gravity. This increase in pressure causes venous distension in the legs and thus more blood is stored in these veins. Subsequently, increased pressure causes a reduction in end diastolic pressure, preload, stroke volume and mean arterial pressure.
120
Briefly explain how the skeletal muscle pump works
When muscle contracts, it gets shorter and fatter and it pushes the veins flat. This action of flattening the veins pushes the blood along the veins.
The blood pushed along he veins can only travel back towards the heart due to the presence of peripheral vein valves.
121
Briefly explain how the respiratory pump works
When you inhale, you produce a negative pressure in the chest and a positive pressure in the abdomen as the diaphragm is pulled down. So, each time you inhale, you get a bigger driving force pushing the blood up the inferior vena cava towards the heart. On expiration, the pressure change should push blood back down the vena cava but the presence of valves means that the blood cannot be pushed down, it can only be pulled up.
The faster and deeper you breathe, the more blood you pull back to the heart and the greater the end diastolic volume becomes.
122
What is venomotor tone?
Smooth muscle around the outside of a venue/vein can be constricted by sympathetic innervation. The constriction pushes the blood forward
123
Name the three different types of capillary and explain how they are different
- Continuous capillaries have either no clefts or pores or they have only clefts
- Fenestrated capillaries have both clefts and pores. These capillary types are specialised for fluid exchange
- Discontinuous capillaries have clefts and massive pores
124
Where in the body would you find continuous capillaries with no clefts or pores?
Blood brain barrier
125
Whew would you find continuous capillaries with clefts?
muscle tissue
126
Where would you find fenestrated capillaries?
Intestine and kidneys
127
Where would you find discontinuous capillaries?
the liver, spleen and bone marrow
128
What is the difference between a cleft and a pore?
Clefts are the spaces between the endothelial cells that make up the capillary wall while pores are small holes in an endothelial cell
129
Name the two ways in which exchange can happen in capillaries
Diffusion
| Bulk flow
130
What is hydrostatic pressure?
The pressure pushing fluid out of a vessel
131
What is oncotic pressure?
The pressure pushing fluid into a vessel
132
What happens to hydrostatic pressure as you move through an arteriole towards a capillary?
It becomes less and less
133
What happens to the fluid concentration as it moves through capillaries?
The fluid becomes more concentrated as it looses water but retains the proteins which are too big to leave the vessel. This causes a build-up in osmotic pressure which draws water back in
134
How much fluid is lost and regained through the capillary system each day and what happens to the remaining fluid that is not reabsorbed back into the capillaries?
20L of fluid is lost and around 17L of fluid is regained each day. The remaining 3L drains into the lymphatic system
135
What is oedema?
the accumulation of excess fluid
136
What causes oedema?
1. Lymphatic obstruction
2. raised central venous pressure caused by ventricular failure
3. Increased capillary permeability (caused by inflammation)
137
How is peripheral flow redirected to the regions that need it?
arterioles constrict and dilate to move blood away from the regions where you don't need it and towards the regions that do need it
138
How is resistance calculated?
resistance = (viscosity x length x 8) / (radius to the power of 4 x pi)
139
How is mean arterial pressure calculated?
cardiac output x total peripheral resistance
140
What are the 4 local intrinsic control mechanisms that can control peripheral flow
1. Active metabolic hyperaemia
2. Pressure/flow auto regulation
3. Reactive hyperaemia
4. the injury response
141
Explain how active metabolic hyperaemia influences peripheral flow
When tissue is metabolically active, it produces metabolites/ increases the production of some metabolites such as CO2, H+ and K+.
These metabolites diffuse into the capillary and stimulate the endothelium of the capillary to produce a paracrine signal called endothelium derived relaxing factor
This EDRF then moves out of the capillary and makes its way to the arteriole smooth muscle.
When EDRF reaches the smooth muscle, it causes it to relax which in turn causes the arteriole to dilate.
Because the radius of the arteriole has become bigger, the resistance in the arteriole will decrease and blood flow will increase.
This increase in blood flow then moves into the capillaries and washes away all of the metabolites which creates a new steady state.
142
Explain how pressure/flow auto regulation influences peripheral blood flow
A decrease in mean arterial pressure causes a reduction in blood flow
This causes metabolites to accumulate in the capillaries.
This then triggers the release of paracrine signals (eg EDRF/NO) from the endothelium which cause the arterioles to dilate
This causes blood flow to return to normal
This adaptation ensures that a tissue maintains its blood supply despite changes in mean arterial pressure
143
Explain how reactive hyperaemia influences peripheral blood flow
Occlusion of a vessel causes a massive build-up of metabolites behind the occulsion
This build-up of metabolites causes the release of the paracrine signal EDRF which causes arteriole dilation.
When the occlusion (e.g. a blood pressure cuff) is then removed, the blood from the dilated arterioles rushes into the capillary and the previously occluded tissue goes bright red
144
Explain how the injury response influences peripheral blood flow
When you scratch the skin, you activate C-fibres
which evoke action potentials that are transmitted centrally to the spinal cord (to let you know it hurts).
The action potential also locally triggers he release if substance P, a peptide that acts on mast cells within the skin and triggers the release of histamine.
Histamine causes the dilation of arterioles and makes the junctions between endothelial capillary cells open up
145
List the 6 extrinsic mechanisms which control peripheral blood flow
1. The sympathetic nervous system
2. Parasympathetic nervous system
3. Adrenaline
4. Angiotensin II
5. Vasopressin
6. Atrial natriuretic factor
146
Explain how the sympathetic nervous system influences peripheral blood flow
The sympathetic nervous system releases noradrenaline which binds to alpha1-receptors causing arteriolar constriction
147
Where in the body does the parasympathetic nervous system have an influence over peripheral blood flow
genitalia and salivary glands.
148
Other than from the sympathetic nervous system, where in the body would adrenaline be released from?
Adrenal medulla
149
What stimulates the release of angiotensin II and what effect will it have?
produced in response to low blood volume. It causes arteriolar constriction
150
What stimulates the release of vasopressin and what effect does it have on arterioles?
Produced in response to a low blood volume. It causes arteriole constriction
151
What is atrial natriuretic factor released in response to and what effect does it have on arterioles?
It is released in response to high blood volume and it cause arteriole dilation
152
How does the heart overcome the fact that the coronary arteries are occluded by systole?
Excellent active hyperaemia
Coronary vessels also express many beta2-receptors on the smooth muscle which causes to arteriole dilation when noradrenaline is released
