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1MB Cardiology > Physiology > Flashcards

Physiology Flashcards

1
Q

What is meant by autorhythmicity of the heart?

A

It is able to generate its own electrical impulses without external stimuli

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2
Q

Where does excitation of the heart normally originate?

A

SA node

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3
Q

What are the specialised cells within the SA node that initiate the heart beat called?

A

Pacemaker cells

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4
Q

What is meant by sinus rhythm?

A

Describes the heart’s pace being controlled by the SA node

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5
Q

SA node cells have a stable resting membrane potential. True/False?

A

False

They exhibit spontaneous pacemaker potential

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6
Q

What is the function of the spontaneous pacemaker potential?

A

Takes the membrane potential to threshold (depolarisation) to generate an action potential

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7
Q

What gives rise to pacemaker potential?

A

Decrease in K+ efflux

Slow Na+ influx

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8
Q

What causes the rising phase of the action potential (depolarisation) in SA node cells?

A

Opening of Ca++ channels, resulting in Ca++ influx

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9
Q

What causes the falling phase of the action potential (repolarisation) in SA node cells?

A

Opening of K+ channels, resulting in K+ efflux

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10
Q

Summarise the phases of the SA node action potential

A

Pacemaker potential: decreased K+ efflux, slow Na+ influx
Rising phase: Ca++ influx
Falling phase: K+ efflux

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11
Q

Which junctions allow cell-to-cell spread of excitation?

A

Gap junctions

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12
Q

The AV node is the only point of electrical contact between atria and ventricles. True/False?

A

True

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13
Q

AV node cells are large and slow to conduct. True/False?

A

False

They are small and slow to conduct

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14
Q

Why is AV nodal delay present?

A

To allow time for atrial systole to precede ventricular systole

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15
Q

Which fibres enable the excitation to spread to the ventricles?

A

Bundle of His and Purkinje fibres

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16
Q

What gives rise to the rising phase of the action potential in ventricular contractile cells?

A

Fast Na+ influx

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17
Q

Describe Phase 0 of the cardiac action potential

A

Fast Na+ influx causes reversal of the resting membrane potential from -90mV to +30mV

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18
Q

Describe Phase 1 of the cardiac action potential

A

Closure of Na+ channels + transient K+ efflux causes some repolarisation

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19
Q

What gives rise to the plateau phase (phase 2) of the cardiac action potential?

A

Ca++ influx

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20
Q

What gives rise to the falling phase (phase 3) of the cardiac action potential?

A

K+ efflux

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21
Q

Describe Phase 3 of the cardiac action potential

A

Closure of Ca++ channels and opening of K+ channels allows K+ efflux which causes repolarisation of the membrane potential back to -90mV

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22
Q

Sympathetic stimulation causes increased heart rate. True/False?

A

True

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23
Q

What is meant by vagal tone?

A

Parasympathetic stimulation to the heart dominating in resting conditions

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24
Q

The vagus nerve supplies only the SA node. True/False?

A

False

Supplies both SA and AV nodes

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25
Q

What does parasympathetic stimulation do to the AV node?

A

Increases AV nodal delay

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26
Q

Which neurotransmitter acts on which receptor in parasympathetic control of the heart?

A

ACh on M2 receptors

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27
Q

Name a competitive inhibitor of ACh that is used in bradycardia

A

Atropine

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28
Q

Vagal stimulation causes the slope of the pacemaker potential to increase. True/False?

A 
False
Slope decreases (increased AV node delay)
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29
Q

What is meant by negative chronotropic effect?

A

Decreased contraction of the heart due to less frequent action potentials

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30
Q

Which areas of the heart does the sympathetic system supply?

A

SA node
AV node
Myocardium

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31
Q

Which neurotransmitter acts on which receptor in sympathetic control of the heart?

A

Noradrenaline on B1 receptors

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32
Q

Sympathetic stimulation does what to the slope of the action potential?

A

Increases it

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33
Q

What is meant by positive chronotropic effect?

A

Increased contraction of the heart due to more frequent action potentials

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34
Q

Where does Lead I of an ECG connect?

A

Right arm - Left arm

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35
Q

Where does Lead II of an ECG connect?

A

Right arm - Left leg

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36
Q

Where does Lead III of an ECG connect?

A

Left arm - Left leg

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37
Q

Cardiac muscle is striated. True/False?

A

True

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38
Q

What creates the striated appearance of cardiac muscle?

A

Contractile protein elements (actin and myosin)

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39
Q

Give the name of protein channels that which form electrical communication between neighbouring myocytes

A

Gap junctions

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40
Q

What do desmosomes do in the heart?

A

Provide mechanical adhesion between adjacent cardiac cells

Ensure tension is developed

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41
Q

What is contained within muscle fibres?

A

Myofibrils (contractile protein elements of muscle)

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42
Q

Actin filaments are thick and appear light. True/False?

A

False

They appear light but are thin

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43
Q

Myosin filaments are thick and appear dark. True/False?

A

True

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44
Q

What is the arrangement of of actin and myosin within each myofibril called?

A

Sarcomere

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45
Q

Myosin filaments slide over actin filaments to produce muscle tension. True/False?

A

False

Actin slides over myosin!

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46
Q

What is required to generate the force by which sliding of filaments can occur?

A

ATP

Calcium

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47
Q

What is the role of calcium in sliding of filaments?

A

Required to ‘switch on’ cross-bridge formation

  1. binds to troponin complex on myosin
  2. causes conform change which exposes actin binding site
  3. cross-bridge forms via site and myosin binding site
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48
Q

What is the role of ATP in sliding of filaments?

A

Binds to myosin head to either energise it or break down the cross-bridge between myofibrils (that is created by calcium)

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49
Q

Where does the calcium that activates contractile machinery come from (where is it stored)?

A

Sarcoplasmic reticulum

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50
Q

What is meant by calcium-induced calcium release?

A

Ca++ influx during the plateau phase of the AP causes Ca++ to be released from the sarcoplasmic reticulum to cause contraction

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51
Q

What is meant by the refractory period?

A

Period following action potential where it is not possible to generate another action potential

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52
Q

What are the two moments where a new action potential cannot be generated?

A 
Plateau phase (Na channels in closed state)
Falling phase (K channels open, thus membrane cannot depolarise)
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53
Q

What is the clinical benefit of the refractory period?

A

Prevents tetanic contractions of the heart

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54
Q

Define stroke volume

A

Volume of blood ejected by each ventricle per heart beat

EDV - ESV

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55
Q

What is meant by end diastolic volume (EDV)?

A

Volume of blood remaining in each ventricle following diastole

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56
Q

What determines EDV?

A

Venous return

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57
Q

Describe the Frank-Starling Law of the Heart

A

The greater the EDV (as a result of more venous return), the greater the stroke volume will be during systole

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58
Q

Optimal skeletal muscle fibre length (for contraction) is achieved by stretching the muscle. True/False?

A

False

Optimal length is at rest

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59
Q

What is meant by preload?

A

Volume of blood in each ventricle before contraction

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60
Q

What is meant by afterload?

A

The resistance against which the heart has to pump after contraction

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61
Q

How does the Frank-Starling law compensate partially for decreased stroke volume?

A

EDV increases (due to failure to pump full SV) so force of contraction increases

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62
Q

What is meant by positive inotropic effect?

A

Force of contraction increases (due to sympathetic stimulation)

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63
Q

Parasympathetic system has a negative chronotropic and inotropic effect. True/False?

A

False

No inotropic effect

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64
Q

What does sympathetic stimulation do to the Frank-Starling curve?

A

Shifts it to the left (increased SV)

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65
Q

What is meant by cardiac output?

A

Volume of blood pumped out by each ventricle per minute

SV x HR

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66
Q

Cardiac valves produce a sound when they open and close. True/False?

A

False

Only produce a sound when they close (normally)

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67
Q

What is the cardiac cycle?

A

Encompasses all the events from one heartbeat to the next

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68
Q

What happens in Passive Filling?

A

AV valves open and blood flows into ventricles

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69
Q

80% of ventricular filling is done by atrial contraction. True/False?

A

False

80% is contributed to by passive filling

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70
Q

In Passive Filling, what are the pressures in the atria and ventricles?

A

Close to zero

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71
Q

What happens in Atrial Contraction?

A

Remaining atrial volume fills ventricles by atrial systole, completing the EDV

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72
Q

Which part of the ECG signals atrial depolarisation?

A

P wave

73
Q

During which part of the ECG do the atria contract?

A

Between the P wave and QRS complex

74
Q

What happens in Isovolumetric Ventricular Contraction?

A

AV valves shut since Patria less than Pventricles (produces S1)
Ventricle is essentially a closed box of high pressure

75
Q

Which part of the ECG signals ventricular depolarisation?

A

QRS complex

76
Q

When does ventricular systole take place on the ECG?

A

Between end of QRS and beginning of T wave (ST segment)

77
Q

What happens in Ventricular Ejection?

A

Aortic/pulmonary valve opens since Pventricles is greater
Stroke volume is ejected; ESV remains
Ventricular pressure falls and aortic/pulmonary valve shuts since P here less than Pventricles (produces S2)

78
Q

What produces the dicrotic notch in the aortic pressure curve?

A

Aortic valve closing

79
Q

What happens in Isovolumetric Ventricular Relaxation?

A

Ventricle is a closed box again (since aortic/pulmonary valves have closed)
Pressure falls until Pventricles less than Patria, where AV valves open and whole cycle restarts

80
Q

S1 heralds the end of systole. True/False?

A

False

Heralds the start of systole (AV valves shut)

81
Q

S2 heralds the start of diastole. True/False?

A

True

82
Q

Define ‘blood pressure’

A

Outward force exerted by blood on blood vessel walls

83
Q

Arterial laminar flow is audible. True/False?

A

False

84
Q

If external pressure exceeds systolic blood pressure, sound will be heard through a stethoscope. True/False?

A

False

85
Q

Which sort of blood flow can be heard through a stethoscope?

A

Turbulent

86
Q

What is the 1st Korotkoff sound?

A

Peak systolic pressure

87
Q

What are the 2nd-3rd Korotkoff sounds?

A

Intermittent sounds of turbulent flow

88
Q

What is the 4th Korotkoff sound?

A

Last muffled sound heard before sound stops

89
Q

What is the 5th Korotkoff sound?

A

No sound!

Represents diastolic pressure

90
Q

What are the formulae for calculating MAP?

A

[2 x diastolic + systolic]/3
diastolic + [systolic - diastolic]/3
CO x TPR
SV x HR x TPR

91
Q

What is the normal range for MAP?

A

70-105 mm Hg

92
Q

MAP of at least 50 mm Hg is needed to perfuse the vital organs. True/False?

A

False

At least 60 mm Hg is needed

93
Q

Arteries are the main resistance vessels. True/False?

A

False

94
Q

What are the main resistance vessels?

A

Arterioles

95
Q

Which receptors regulate blood pressure short-term?

A

Baroreceptors

96
Q

The higher the blood pressure, the greater the firing of baroreceptors. True/False?

A

True

97
Q

Which CN do the carotid baroreceptors fire through?

A

CN IX

98
Q

Which CN do the aortic baroreceptors fire through?

A

CN X

99
Q

When arterial blood pressure decreases, what happens with regards to baroreceptors?

A

Decreased firing, causing decreased vagal activity, causing increased sympathetic activity, causing increased vasoconstriction, leading to increase in blood pressure

100
Q

When you suddenly stand up, what happens to the venous return to the heart and thus MAP?

A

Decreases

101
Q

How much of total body fluid does extracellular fluid contribute to?

A

1/3

102
Q

What is the function of renin in the RAAS?

A

Released from kidneys to stimulate conversion of angiotensinogen to angiotensin I

103
Q

What is the function of ACE?

A

Converts angiotensin I to angiotensin II

104
Q

What is the function of angiotensin II?

A

Stimulates release of aldosterone

Causes systemic vasoconstriction

105
Q

What is the function of aldosterone in the RAAS?

A

Acts on kidneys to increase Na+ and water retention

106
Q

Where is renin released from?

A

Juxtapulmonary apparatus in the kidney

107
Q

Renal artery hypertension causes renin to be released. True/False?

A

False

Hypotension would cause its release

108
Q

Where is ANP stored?

A

Atrial myocytes

109
Q

What does ANP do?

A

Causes excretion of Na+ and water in the kidneys
Vasodilates
Decreases renin release
[counteracts RAAS]

110
Q

When is ADH release stimulation?

A

Reduced extracellular fluid

Increased extracellular fluid osmolarity (solute)

111
Q

What does ADH do?

A

Causes reabsorption of water, i.e. concentrates urine, to increase plasma volume
Vasoconstriction (small degree)

112
Q

Which blood vessel holds the most blood volume at rest?

A

Veins

113
Q

Resistance to blood flow is directly proportional to what?

A

Thickness and length of blood vessel

114
Q

Resistance to blood flow is inversely proportional to what?

A

[Radius of blood vessel]^4

115
Q

How is resistance to blood flow mainly controlled?

A

Through changes in the radius of the vessel

116
Q

What is meant by vasomotor tone?

A

Vascular smooth muscle being partially constricted at rest due to tonic discharge of the sympathetic system (releases noradrenaline)

117
Q

There is no parasympathetic innervation of vascular smooth muscle. True/False?

A

False

There is in the penis and clitoris

118
Q

Adrenaline acting on alpha receptors causes what?

A

Vasoconstriction

119
Q

Adrenaline acting on beta receptors causes what?

A

Vasodilation

120
Q

Alpha receptors are predominant in skeletal and cardiac muscle arterioles. True/False?

A

False

Beta receptors are predominant here

121
Q

Where are alpha receptors predominately found?

A

Skin, gut and kidney arterioles

122
Q

What is the effect of angiotensin II on vascular smooth muscle?

A

Vasoconstriction

123
Q

Local metabolic conditions can override extrinsic control of vascular smooth muscle. Explain?

A

You can have local vasodilation at an organ, despite widespread vasoconstriction, and this will not influence overall blood pressure

124
Q

Decreased local PO2 causes vasoconstriction in systemic circulation. True/False?

A

False

Causes vasodilation

125
Q

What is the effect of decrease in local PO2 in pulmonary circulation arterial smooth muscle?

A

Vasoconstriction

126
Q

Increased local [H+] and [K+] in systemic circulation causes vasodilation. True/False?

A

True

127
Q

Name some humoral agents that are potent vasodilators

A

Histamine
Bradykinin
Prostaglandins
Nitric oxide

128
Q

Name some humoral agents that are potent vasoconstrictors

A

Serotonin
Thromboxane A2
Leukotrienes
Endothelin

129
Q

Describe myogenic response to stretch

A

If MAP falls, resistance vessels in brain and kidneys dilate to increase flow (i.e. not in line with normal baroreceptor reflex)

130
Q

Sympathetic stimulation increases during exercise. What does this do to the HR, SV and CO?

A

Increases all of them

131
Q

How does blood flow change to the kidney and gut during exercise?

A

Decreases - vasomotor tone causes vasoconstriction in these areas

132
Q

How does blood flow change to skeletal and cardiac muscle during exercise?

A

Increases due to vasodilation in these areas

133
Q

What causes vasodilation in skeletal and cardiac muscle during exercise? i.e. what overrides sympathetic effects?

A

Metabolic hyperraemia

134
Q

Systolic and diastolic murmurs coincide with the carotid pulse. True/False?

A

False

Only systolic murmurs coincide with carotid pulse

135
Q

Physiological splitting of the 2nd heart sound occurs on inspiration. True/False?

A

True

136
Q

What happens in physiological splitting of the 2nd heart sound?

A

Inspiration causes decrease in intrathoracic pressure, causing increase in venous return which prolongs RV ejection time (so pulmonary sound delayed fractionally behind aortic sound)

137
Q

A 4th heart sound is always pathological. True/False?

A

True

138
Q

Define ‘shock’

A

An abnormality in the circulatory system, resulting in inadequate tissue perfusion and oxygenation

139
Q

Which 3 factors influence the stroke volume?

A

Preload (venous return)
Myocardial contractility
Afterload

140
Q

How does hypovolaemic shock arise?

A

Loss of blood volume leads to decreased venous return leads to decreased stroke volume leads to decreased CO + BP = low perfusion and oxygenation

141
Q

How does cardiogenic shock arise?

A

Decreased myocardial contractility leads to decreased stroke volume leads to decreased CO + BP = low perfusion and oxygenation

142
Q

How does tension pneumothorax lead to obstructive shock?

A

Increased intrathoracic pressure leads to decreased venous return leads to decreased stroke volume leads to decreased CO + BP = low perfusion and oxygenation

143
Q

How does neurogenic shock arise?

A

Loss of sympathetic (vasomotor) tone leads to increased vasodilation leads to decreased venous return leads to decreased stroke volume leads to decreased CO + BP = low perfusion and oxygenation

144
Q

How does vasoactive shock arise?

A

Release of vasoactive mediators leads to increased vasodilation leads to decreased venous return leads to decreased stroke volume leads to decreased CO + BP = low perfusion and oxygenation

145
Q

Compensatory mechanisms exist to deal with blood volume loss until greater than 40% is lost. True/False?

A

False

Mechanisms only compensate until greater than 30% volume is lost

146
Q

What are the first branches/arteries that come off the aorta?

A

Right + left coronary arteries

147
Q

What drains coronary venous blood into the right atrium?

A

Coronary sinus

148
Q

Which organ has the greatest oxygen demand?

A

The heart

149
Q

The heart can increase the amount of oxygen extracted in order to improve its oxygenation. True/False?

A

False

It already extracts 75% of total, could not extract more

150
Q

How is the oxygen supply to the heart increased, if not by increasing oxygen extraction?

A

Increase coronary blood flow

151
Q

Decreased PO2 causes coronary vasoconstriction. True/False?

A

False

Need to improve oxygenation, therefore vasodilation occurs to increase blood flow

152
Q

Decreased PO2 causes pulmonary vasoconstriction. True/False?

A

True

153
Q

Describe the mechanism by which sympathetic stimulation (indirectly) causes coronary vasodilation

A

Sympathetic tone causes increased HR + SV and hence CO (which itself dilates coronary arteries);
This increases cardiac work and metabolism, consuming O2 (leading to decreased PO2, increased ADP) and releasing metabolites, all of which cause vasodilation;
Adrenaline also acts on B2 to cause vasodilation

154
Q

What effect do K+, H+ and CO2 have on coronary arteries?

A

Vasodilation

155
Q

When does peak coronary flow occur?

A

Diastole

156
Q

Which arteries supply the brain?

A

Internal carotid arteries

Vertebral arteries

157
Q

Which brain matter - grey or white - is very sensitive to hypoxia?

A

Grey matter

158
Q

Which arteries make up the Circle of Willis?

A

Internal carotids + basilar artery (formed by both vertebral arteries joining)

159
Q

The baroreceptor reflex affects the brain. True/False?

A

False

160
Q

If MAP rises, cerebral vessels constrict. True/False?

A

True

161
Q

If MAP falls, cerebral vessels dilate. True/False?

A

True

162
Q

When does autoregulation of cerebral blood flow fail?

A

When MAP is less than 60 or greater than 160 mm Hg

163
Q

Decreased PCO2 results in cerebral vasodilation. True/False?

A

False

Results in vasoconstriction - this is why hyperventilation leads to fainting

164
Q

Head injury and tumours increase intracranial pressure. How does this affect cerebral blood flow?

A

Decreases it

165
Q

Decreased O2 does what to pulmonary arterioles? Why?

A

Vasoconstriction (opposite to systemic circulation)

Redirects blood to alveoli to get more oxygen

166
Q

2/3 of body water is extracellular. True/False?

A

False

2/3 is intracellular

167
Q

What is the function of capillaries?

A

Rapid exchange of gases, water and solutes with the interstitial fluid

168
Q

Describe net filtration pressure

A

Forces favouring filtration - forces favouring absorption

169
Q

Forces favouring filtration are stronger at the venule end. True/False?

A

False

Filtration is stronger at the arterial end

170
Q

Forces favouring absorption are stronger at the venule end. True/False?

A

True

171
Q

What are the forces favouring filtration?

A

Capillary hydrostatic pressure (Pc)

Interstitial fluid osmotic pressure (πi)

172
Q

What are the forces favouring absorption?

A

Capillary osmotic pressure (πc)

Interstitial fluid hydrostatic pressure (Pi)

173
Q

What is the main contributor to capillary hydrostatic pressure (Pc)?

A

Blood flow

Tends to force blood out of capillary

174
Q

What is the main contibutor to capillary osmotic pressure (πc)?

A

Presence of plasma proteins

Tends to force blood into capillary

175
Q

How is net filtration pressure calculated using forces described previously?

A

(Pc + πi) - (πc - Pi)

176
Q

Pulmonary capillary hydrostatic pressure is high compared to systemic hydrostatic pressure. True/False?

A

False

177
Q

What is oedema? How does it affect diffusion?

A

Accumulation of fluid in the interstitial space

Increases distance over which diffusion must take place

178
Q

LV failure causes pulmonary oedema. True/False?

A

True

179
Q

How does reduced capillary osmotic pressure cause oedema?

A

Reduces force driving blood back into capillary (osmotic pressure, mainly due to plasma proteins), so fluid accumulates

1MB Cardiology (17 decks)

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