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Flashcards in Physiology Deck (179):
1

What is meant by autorhythmicity of the heart?

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

2

Where does excitation of the heart normally originate?

SA node

3

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

Pacemaker cells

4

What is meant by sinus rhythm?

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

5

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

False
They exhibit spontaneous pacemaker potential

6

What is the function of the spontaneous pacemaker potential?

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

7

What gives rise to pacemaker potential?

Decrease in K+ efflux
Slow Na+ influx

8

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

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

9

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

Opening of K+ channels, resulting in K+ efflux

10

Summarise the phases of the SA node action potential

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

11

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

Gap junctions

12

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

True

13

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

False
They are small and slow to conduct

14

Why is AV nodal delay present?

To allow time for atrial systole to precede ventricular systole

15

Which fibres enable the excitation to spread to the ventricles?

Bundle of His and Purkinje fibres

16

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

Fast Na+ influx

17

Describe Phase 0 of the cardiac action potential

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

18

Describe Phase 1 of the cardiac action potential

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

19

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

Ca++ influx

20

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

K+ efflux

21

Describe Phase 3 of the cardiac action potential

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

22

Sympathetic stimulation causes increased heart rate. True/False?

True

23

What is meant by vagal tone?

Parasympathetic stimulation to the heart dominating in resting conditions

24

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

False
Supplies both SA and AV nodes

25

What does parasympathetic stimulation do to the AV node?

Increases AV nodal delay

26

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

ACh on M2 receptors

27

Name a competitive inhibitor of ACh that is used in bradycardia

Atropine

28

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

False
Slope decreases (increased AV node delay)

29

What is meant by negative chronotropic effect?

Decreased contraction of the heart due to less frequent action potentials

30

Which areas of the heart does the sympathetic system supply?

SA node
AV node
Myocardium

31

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

Noradrenaline on B1 receptors

32

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

Increases it

33

What is meant by positive chronotropic effect?

Increased contraction of the heart due to more frequent action potentials

34

Where does Lead I of an ECG connect?

Right arm - Left arm

35

Where does Lead II of an ECG connect?

Right arm - Left leg

36

Where does Lead III of an ECG connect?

Left arm - Left leg

37

Cardiac muscle is striated. True/False?

True

38

What creates the striated appearance of cardiac muscle?

Contractile protein elements (actin and myosin)

39

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

Gap junctions

40

What do desmosomes do in the heart?

Provide mechanical adhesion between adjacent cardiac cells
Ensure tension is developed

41

What is contained within muscle fibres?

Myofibrils (contractile protein elements of muscle)

42

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

False
They appear light but are thin

43

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

True

44

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

Sarcomere

45

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

False
Actin slides over myosin!

46

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

ATP
Calcium

47

What is the role of calcium in sliding of filaments?

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

48

What is the role of ATP in sliding of filaments?

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

49

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

Sarcoplasmic reticulum

50

What is meant by calcium-induced calcium release?

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

51

What is meant by the refractory period?

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

52

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

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

53

What is the clinical benefit of the refractory period?

Prevents tetanic contractions of the heart

54

Define stroke volume

Volume of blood ejected by each ventricle per heart beat
EDV - ESV

55

What is meant by end diastolic volume (EDV)?

Volume of blood remaining in each ventricle following diastole

56

What determines EDV?

Venous return

57

Describe the Frank-Starling Law of the Heart

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

58

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

False
Optimal length is at rest

59

What is meant by preload?

Volume of blood in each ventricle before contraction

60

What is meant by afterload?

The resistance against which the heart has to pump after contraction

61

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

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

62

What is meant by positive inotropic effect?

Force of contraction increases (due to sympathetic stimulation)

63

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

False
No inotropic effect

64

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

Shifts it to the left (increased SV)

65

What is meant by cardiac output?

Volume of blood pumped out by each ventricle per minute
SV x HR

66

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

False
Only produce a sound when they close (normally)

67

What is the cardiac cycle?

Encompasses all the events from one heartbeat to the next

68

What happens in Passive Filling?

AV valves open and blood flows into ventricles

69

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

False
80% is contributed to by passive filling

70

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

Close to zero

71

What happens in Atrial Contraction?

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

72

Which part of the ECG signals atrial depolarisation?

P wave

73

During which part of the ECG do the atria contract?

Between the P wave and QRS complex

74

What happens in Isovolumetric Ventricular Contraction?

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

75

Which part of the ECG signals ventricular depolarisation?

QRS complex

76

When does ventricular systole take place on the ECG?

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

77

What happens in Ventricular Ejection?

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

What produces the dicrotic notch in the aortic pressure curve?

Aortic valve closing

79

What happens in Isovolumetric Ventricular Relaxation?

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

S1 heralds the end of systole. True/False?

False
Heralds the start of systole (AV valves shut)

81

S2 heralds the start of diastole. True/False?

True

82

Define 'blood pressure'

Outward force exerted by blood on blood vessel walls

83

Arterial laminar flow is audible. True/False?

False

84

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

False

85

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

Turbulent

86

What is the 1st Korotkoff sound?

Peak systolic pressure

87

What are the 2nd-3rd Korotkoff sounds?

Intermittent sounds of turbulent flow

88

What is the 4th Korotkoff sound?

Last muffled sound heard before sound stops

89

What is the 5th Korotkoff sound?

No sound!
Represents diastolic pressure

90

What are the formulae for calculating MAP?

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

91

What is the normal range for MAP?

70-105 mm Hg

92

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

False
At least 60 mm Hg is needed

93

Arteries are the main resistance vessels. True/False?

False

94

What are the main resistance vessels?

Arterioles

95

Which receptors regulate blood pressure short-term?

Baroreceptors

96

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

True

97

Which CN do the carotid baroreceptors fire through?

CN IX

98

Which CN do the aortic baroreceptors fire through?

CN X

99

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

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

100

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

Decreases

101

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

1/3

102

What is the function of renin in the RAAS?

Released from kidneys to stimulate conversion of angiotensinogen to angiotensin I

103

What is the function of ACE?

Converts angiotensin I to angiotensin II

104

What is the function of angiotensin II?

Stimulates release of aldosterone
Causes systemic vasoconstriction

105

What is the function of aldosterone in the RAAS?

Acts on kidneys to increase Na+ and water retention

106

Where is renin released from?

Juxtapulmonary apparatus in the kidney

107

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

False
Hypotension would cause its release

108

Where is ANP stored?

Atrial myocytes

109

What does ANP do?

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

110

When is ADH release stimulation?

Reduced extracellular fluid
Increased extracellular fluid osmolarity (solute)

111

What does ADH do?

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

112

Which blood vessel holds the most blood volume at rest?

Veins

113

Resistance to blood flow is directly proportional to what?

Thickness and length of blood vessel

114

Resistance to blood flow is inversely proportional to what?

[Radius of blood vessel]^4

115

How is resistance to blood flow mainly controlled?

Through changes in the radius of the vessel

116

What is meant by vasomotor tone?

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

117

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

False
There is in the penis and clitoris

118

Adrenaline acting on alpha receptors causes what?

Vasoconstriction

119

Adrenaline acting on beta receptors causes what?

Vasodilation

120

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

False
Beta receptors are predominant here

121

Where are alpha receptors predominately found?

Skin, gut and kidney arterioles

122

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

Vasoconstriction

123

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

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

124

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

False
Causes vasodilation

125

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

Vasoconstriction

126

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

True

127

Name some humoral agents that are potent vasodilators

Histamine
Bradykinin
Prostaglandins
Nitric oxide

128

Name some humoral agents that are potent vasoconstrictors

Serotonin
Thromboxane A2
Leukotrienes
Endothelin

129

Describe myogenic response to stretch

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

130

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

Increases all of them

131

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

Decreases - vasomotor tone causes vasoconstriction in these areas

132

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

Increases due to vasodilation in these areas

133

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

Metabolic hyperraemia

134

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

False
Only systolic murmurs coincide with carotid pulse

135

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

True

136

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

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

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

True

138

Define 'shock'

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

139

Which 3 factors influence the stroke volume?

Preload (venous return)
Myocardial contractility
Afterload

140

How does hypovolaemic shock arise?

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

141

How does cardiogenic shock arise?

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

142

How does tension pneumothorax lead to obstructive shock?

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

143

How does neurogenic shock arise?

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

How does vasoactive shock arise?

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

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

False
Mechanisms only compensate until greater than 30% volume is lost

146

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

Right + left coronary arteries

147

What drains coronary venous blood into the right atrium?

Coronary sinus

148

Which organ has the greatest oxygen demand?

The heart

149

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

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

150

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

Increase coronary blood flow

151

Decreased PO2 causes coronary vasoconstriction. True/False?

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

152

Decreased PO2 causes pulmonary vasoconstriction. True/False?

True

153

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

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

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

Vasodilation

155

When does peak coronary flow occur?

Diastole

156

Which arteries supply the brain?

Internal carotid arteries
Vertebral arteries

157

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

Grey matter

158

Which arteries make up the Circle of Willis?

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

159

The baroreceptor reflex affects the brain. True/False?

False

160

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

True

161

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

True

162

When does autoregulation of cerebral blood flow fail?

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

163

Decreased PCO2 results in cerebral vasodilation. True/False?

False
Results in vasoconstriction - this is why hyperventilation leads to fainting

164

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

Decreases it

165

Decreased O2 does what to pulmonary arterioles? Why?

Vasoconstriction (opposite to systemic circulation)
Redirects blood to alveoli to get more oxygen

166

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

False
2/3 is intracellular

167

What is the function of capillaries?

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

168

Describe net filtration pressure

Forces favouring filtration - forces favouring absorption

169

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

False
Filtration is stronger at the arterial end

170

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

True

171

What are the forces favouring filtration?

Capillary hydrostatic pressure (Pc)
Interstitial fluid osmotic pressure (πi)

172

What are the forces favouring absorption?

Capillary osmotic pressure (πc)
Interstitial fluid hydrostatic pressure (Pi)

173

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

Blood flow
Tends to force blood out of capillary

174

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

Presence of plasma proteins
Tends to force blood into capillary

175

How is net filtration pressure calculated using forces described previously?

(Pc + πi) - (πc - Pi)

176

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

False

177

What is oedema? How does it affect diffusion?

Accumulation of fluid in the interstitial space
Increases distance over which diffusion must take place

178

LV failure causes pulmonary oedema. True/False?

True

179

How does reduced capillary osmotic pressure cause oedema?

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