B2 Physiology of Cardiac Muscle Flashcards Preview

Phase I Medicine > B2 Physiology of Cardiac Muscle > Flashcards

Flashcards in B2 Physiology of Cardiac Muscle Deck (223):
1

What are the functional parts of the cardiac muscle?

Myocyte
Sarcomere
Actin & Myosin
Troponin & Tropomyosin

2

What is a myocyte?

Bundles of spirally arranged myofibrils

3

How many myosin molecules are in a myofilament?

300

4

What are myocytes made from?

Myofilaments

5

What is a sarcomere?

Basic individual contractile unit
The distance between two Z lines on a myofibril?

6

What are myofilaments made from?

Myofibrils

7

How do sarcomeres relate to muscle contraction?

Shortening of lots of sarcomeres - muscle contraction

8

What is actin?

Thin filament contributing to structure of sarcomere

9

What is myosin?

Thick filament contributing to structure of sarcomere; has two heads

10

What does myosin contain that is necessary for muscle contraction?

ATPase

11

What is regulatory protein complex?

Thin filaments which are made up of actin and a chain of globular protein.

12

What are the three types of troponin?

T
C
I

13

What is the role of Troponin T?

Tropomyosin attachment

14

What is the role of Troponin C?

Ca2+ binding (when it's released from sarcoplasmic reticulum)

15

What is the role of Troponin I?

Inhibits actin and myosin binding (Until troponin C has bound Ca2+)

16

When are troponin and tropomyosin present in the blood?

After myocyte damage (e.g. heart attack)

17

What is the first step of excitation - contraction coupling (ECC)?

Receptors activated at neuromuscular synapse

18

What happens after receptor activation in the ECC process?

Release of Ca2+ from sarcoplasmic reticulum

19

What happens after Ca2+ is released from the sarcoplasmic reticulum?

Troponin- I is released from the troponin molecule

20

What happens to the actin to allow cross linking of actin and myosin?

Myosin binding sites are exposed

21

What happens after cross linking of the two filaments?

ATP attaches to the myosin head

22

What effect does the ATP attachment have on the filaments?

Cross bridges detach

23

What does the term 'power stroke' mean?

Myosin filaments rotate towards the centre of the sarcomere

24

What happens after the cross bridges detach?

Myosin hydrolyses the ATP

25

What does the myosin head do with the energy from hydrolysed ATP?

Reorientates itself

26

How does contraction occur on the level of the sarcomere?

The myosin stays in the same place but binds to different segments of actin, resulting in actin sliding towards the M line

27

What is the M line?

The vertical mid line of the sarcomere

28

What type of nerve terminal is involved in cardiac muscle contraction?

Sympathetic

29

Where are the nerve terminals in cardiac muscle contraction?

SA and AV nodes

30

What is released at the sympathetic nerve terminals?

Noradrenaline

31

What does noradrenaline bind to on the post-synaptic membrane?

B1 receptors

32

What is the result of noradrenaline binding to B1 receptors in the process of cardiac muscle contraction?

G protein gets activated

33

What is the role of G protein in cardiac muscle contraction?

It converts ATP to cAMP

34

What is the role of cAMP in cardiac muscle contraction?

It activates B-adrenoreceptor kinase

35

What is B-adrenoreceptor kinase?

A protein kinase

36

What is the role of B- adrenoreceptor kinase in cardiac muscle contraction?

Ca2+ in the sarcolemma gets phosphorylated

37

What effect does Ca2+ phosphorylation have on cardiac muscle contraction

Increased Ca2+ means increased speed and force of contraction

38

What is transmembrane potential?

The voltage difference across a cell membrane

39

What causes transmembrane potential?

The accumulation of negative ions within the cell

40

How is a transmembrane potential set up?

Stimulation of the cell

41

What does a transmembrane potential result in?

Ion transfer across the membrane
Voltage change

42

How is an action potential triggered in heart muscle?

Cell to cell depolarisation in cardiac myocytes
Spontaneous in cardiac pacemaker cells

43

What is the difference between action potentials triggered betwene cardiac myocytes and in pacemaker cells

In myocytes there is a fast response
In cardiac pacemaker cells there is a slow response

44

Why are action potentials prolonged in cardiac muscle?

To allow for complete atrial systole before ventricular systole starts.

45

What happens during repolarisation?

K, Na and Ca returns the cell membrane to resting potential

Myocyte in refractory period- will not respond to a further stimulus.

46

What are the cardiac pathways through the heart?

SAN -> AVN -> Bundle of His -> Bundle branches -> Purkinje Fibres

47

How long does the cardiac cycle usually last (how long is a single heart beat)

0.8s

48

What is the average person's heart rate?

72 beats/min

49

What are the two basic components of the cardiac cycle?

Systole and diastole

50

How do you calculate heart rate?

time divided by speed

51

How is the direction of blood flow controlled?

Valves

52

How many phases are in the cardiac cycle?

5

53

What is the first phase of the cardiac cycle?

Atrial systole

54

What does the P wave represent on the ECG?

Atrial systole

55

How much more blood the ventricles from atrial systole?

30%

56

Which valves are open during atrial systole?

Mitral and tricuspid

57

What is the benefit of atrial systole over passive filling of the ventricles?

More blood enters the ventricles
Ventricles are stretched improving the strength of contraction

58

What is Starling's law?

The ability of the heart to change its force of contraction and therefore stroke volume in response to changes in venous return.

59

What is the second phase of the cardiac cycle?

Isometric ventricular contraction

60

What happens to the ventricles in the second phase of the cardiac cycle?

The ventricles change in shape but not volume and the valves are still closed.
Atrial diastole

61

Where is phase 2 of the cardiac cycle on the ECG?

The peak of the QRS complex

62

What causes the first heart sound (S1/'Lub')

The Mitral and Tricuspid valves closing

63

What causes the C wave?

Blood bulging back into the atria and against the valves causing a small pressure increase.

64

What is the third phase of the cardiac cycle?

Ejection phase

65

What happens during the ejection phase of the cardiac cycle?

50%-70% of the ventricular contents is ejected until the pulmonary/aortic valves close

66

What part of the ECG represents the ejection phase?

ST segment

67

When do the aortic and pulmonary valves close?

When the aortic/ pulmonary trunk pressure is higher than the ventricles

68

What causes the second heart sound (S2/'Dub')?

The Aortic and Pulmonary valves closing

69

What is the fourth phase of the cardiac cycle?

Isometric ventricular relaxation

70

What happens during isometric ventricular relaxation?

Cardiac myocytes repolarise
All valves closed
Both chambers are in diastole
Ventricuar pressure falls
Atria fill from veins so the atrial pressure starts to rise

71

What part of the ECG represents isometric ventricular relaxation?

T wave

72

What is the fifth phase of the cardiac cycle?

Slow filling

73

What happens during slow filling?

Mitral/ Tricuspid open
Blood from veins filling atria
Pressure in atria eventually rises to above ventricular pressure

74

What part of the atrial trace represents slow filling?

V wave

75

How much of the venous blood actually enters the ventricles?

70%

76

What factors influence cardiac output?

Stroke volume
Heart rate

77

What is the another name for Starling's law

Frank-Starling Effect

78

Why does a higher diastolic volume mean higher contractility mean a higher stroke volume?

Increasing fibre length results in increased velocity of contraction
Increasing diastolic volume increases the length of the cardiac muscle fibres in the ventricles

79

What does the P-R interval show?

The period of time from onset of P wave to start of QRS complex (normally 0.12-0.2s)

80

What does the Q wave represent?

Excitation of intraventricular septum

81

What does the R wave represent?

Excitation of apex and free walls

82

What does the S wave represent?

Excitation of regions near the base of the heart

83

How long does the QRS complex last?

0.06-0.1s

84

What kind of shape does a normal T wave have?

Assymetrical

85

True or false? The T wave may be followed by a small U wave repolarisation of papillary muscle

True

86

What does the ST segment show?

The period between the end o ventricular depolarisation and the beginning of ventricular repolarisation

87

What does the QT interval show?

Total time taken for depolarisation and repolarisation of the ventricles

88

Why is it that the after a myocardial infarction, the ST segment can appear raised or lowered?

Baseline changes

89

How long is the QT interval on average?

0.35-0.45s

90

True or false? QT interval varies with heart rate?

True

91

What is sinus rhythm?

Heart rhythm is determined by the SA node

92

What cells are responsible for generating the spontaneously unstable membrane potential?

Pacemaker cells

93

What is the normal sinus rate range?

60-100 beats/min

94

What is bradycardia?

Slow heart beat (

95

What is tachycardia?

Fast heart beat (>100 beats/min)

96

What is the commonest form of arrhythmia?

Atrial Fibrillation

97

What increases the prevalence of atrial fibrillation?

Age

98

How is atrial fibrillation caused?

Multiple re-entrant circuits sweeping around atrial myocardium which may hit the SA node causing irregular ventricular contraction

99

How would atrial fibrillation present on an ECG?

P-Waves absent
Wavy irregular baseline of fibrillation waves - 300-600 beats/min

100

What is inotropy?

Force of contraction

101

What is chronotropy?

Timing of impulse firing/ heart rate

102

What is the effect of digoxin on the heart?

Cardiac glycoside
Increases force of contraction
Decreases conduction in AV node

103

What is the effect of adrenaline on the heart?

Increases heart rate, inotropy and automaticity

104

Between digoxin and adrenaline, which drug doesn't have an effect on automaticity?

Digoxin

105

What are adrenaline's pharmalogical mechanisms of action?

Acts on B1-adrenoreceptors via cAMP on SAN, atrial muscle, AVN and ventricular muscle

106

What types of cells does the cardiac muscle have?

Myocardial cells
Conduction cells

107

What are myocardial cells?

Cells responsible for generating pumping pressure to pump blood around body; cells- connected

108

What are conduction cells?

Cells responsible for rapidly spreading electrical signals to myocardial cells

109

How are myocardial cells connected?

Via intercalated discs with gap junctions.

110

Why do conduction cells spread electrical signals to myocardial cells?

To coordinate pumping.

111

Give an example of conduction pathway cells?

Bundle of His
Purkinje fibres

112

What are the three layers in the walls of blood vessels known as?

Tunics

113

What is the innermost layer of a blood vessel, histologically?

Tunica Interna (Intima)

114

What is the middle layer of a blood vessel, histologically?

Tunica Media

115

What are the properties of the tunica interna/intima?

Continuous with endocardial lining of heart
Smooth surface so blood flows through smoothly
Simple squamous epithelium

116

What are the qualities of the simple squamous epithelium in the tunica interna?

Short diffusion path
Site where chemical signals are sent/received
Site for synthesis of various agents

117

What are the qualities of the basement membrane in the tunica interna?

Provides physical support base for epithelial layer.
Framework of collagen fibres
Anchors epithelium to underlying connective tissue
Regulates molecular movement

118

What are the qualities of the internal elastic lamina in the tunica interna?

Thin sheet of elastic fibres
Variable number of window-like openings (facilitate diffusion from tunica interna to tunica media)

119

What allows for the diffusion of materials from the tunica interna to the tunica media?

Window like openings in internal elastic lamina of tunica interna

120

What is the tunica media?

Muscular and connective tissue layer

121

What layer varies the most among different vessel types?

Tunica media

122

What is the primary role of muscle cells?

To regulate the diameter of the lumen

123

What does the tunica media mainly consist of?

Smooth muscle cells
Elastic fibres

124

When does vasoconstriction occur?

Sympathetic stimulation
Vascular spasm to limit blood loss after damage

125

What separates the tunica media from the tunica externa?

External elastic lamina

126

Between the tunica media and the tunica externa, which layer does the external elastic lamina belong to?

Tunica media

127

What is another name for the tunica externa?

Tunica Adventitia

128

What is the tunica externa?

Outer covering of blood vessel

129

What is the tunica externa made from?

Elastic and collagen fibres

130

What type of nerve does the tunica externa contain?

Autonomic

131

What is the term used to describe tiny blood vessels that supply the tissues of the vessel walls?

Vasa vasorum

132

What does vasa vasorum mean?

Vessels to the vessels

133

Where can you see vasa vasorum?

The aorta

134

What are the roles of the vasa vasorum

Supplying vessel wall with nerves and self-vessels
Helps anchor vessels to surrounding tissues

135

What are the roles of the aorta/large arteries?

Contain blood at high pressure
Distributing blood to smaller vessels

136

What are larger arteries known as?

Elastic arteries

137

Why are vasa vasorum frequent on larger arteries

Poor oxygen diffusion across thicker surfaces (i.e. larger arteries)

138

What are smaller arteries known as?

Muscular arteries

139

What is the role of smaller arteries/ arterioles?

Site of flow control since there is a significant pressure drop across arterioles

140

Why are larger arteries more elastic?

They have a greater proportion of tunica media which contains the elastic fibres

141

What are the vessels with the smallest diameter called?

Capillaries

142

What are the qualities of capillaries?

Diameter comparable with blood cells
Extensive network
Total cross sectional area large
Thin walled
Tunica media almost absent
Occasional pericytes

143

What are the three types of capillary?

Continuous
Fenestrated
Discontinuous

144

What is the most common type of capillary?

Continuous

145

What are fenestrated capillaries?

Capillaries found in tissues with high exchange function - endothelium appears to have pores for exchange- these are known as fenestrations

146

What is the structure of fenestrated capillaries?

Regular, contain diaphragm material

147

What organs would have a high exchange function?

Small Intestine
Kidney
Endocrine Glands

148

Where are discontinuous tissues found?

In tissues where there is cell as well as molecule exchange.

149

What organs would have cell as well as molecule exchange?

Liver
Spleen

150

What are the qualities of discontinuous capillaries?

Gaps between endothelial cells
Irregular fenestrations
Large sub-endothelial space
Sub-endothelial space occupied by specialised cells

151

What is the primary purpose of venules and veins?

To be a low pressure collecting system

152

What are the structures of venules and veins?

No internal elastic lamina underlying endothelium
Relatively thin tunica media for lumen size

153

True or false? Venules and veins have the abilility to change their capacity

True - some capacity

154

How do the venules and veins move blood back to the heart?

Valves and 'muscle pump'.

155

What is the cardiac muscle made of?

Cardiac myocytes

156

What junctions are between intercalated disks?

Gap
Adherens

157

How are signals transmitted between intercalated disks?

Electro-chemical coupling
Mechanical link

158

How is it that the heart can function aerobically?

Metabolic substrates

159

What does blood pressure depend on?

Cardiac output and peripheral resistance

160

What factors affect peripheral resistance?

Blood viscosity
Dimensions of vessel
Blood volume

161

What are the properties of lymphatic vessels?

Lined by endothelium
Extremely low pressure
Thin walled (Normally endothelium only)
Valves
Non-continuous circulation

162

Why is lymphatic circulation non-continuous?

It drains fluid from tissues and ultimately drains it into the venous system, it's doesn't find its way back to tissues

163

What does lymph filter through?

Lymph nodes

164

What is the structure of smooth muscle?

Individual long thin cells (spindle shaped)
Actin-myosin contractile system not in sarcomeres
Central oval shaped nuclei

165

In comparison to striated muscle, does smooth muscle have more or less contractility?

More

166

What is the speed of smooth muscle contraction in comparison to striated?

It is slower

167

How is smooth muscle able to maintain tension?

Low ATP consumption

168

Where is smooth muscle typically found?

Walls of vessels and tissues

169

Is smooth muscle somatic or autonomic in terms of nerve control?

Autonomic

170

What kind of pressure do individual tissues generally start off with?

High

171

Why do different tissues have different pressures?

They can choose what blood pressure they want

172

Other than heart rate and peripheral resistance, what else determined cardiac output?

Tissue demand

173

How is tissue flow locally determined?

Tissue demand; acts by changing resistance

174

What formula is used to calculate blood flow?

Change in pressure gradient / Resistance

175

What is the average cardiac output in humans?

5L/min

176

What happens to cardiac output if there is an increase in venous return?

Cardiac output increases

177

True or false? Blood pressure and cardiac output are independent of each other

True

178

How can you relate blood flow to the radius of the vessel?

Flow is proportional to the 4th power of the radius of the vessel.

179

How is blood flow mechanically controlled?

Muscle sphincters in pre-capillary arterioles constrict/open the vessels (changing vessel radius)

180

Is flow within a vessel linear?

No

181

What is the effect of pressure on vessels?

Pressure distends vessels decreasing peripheral resistance

182

What is the effect of blood pressure on blood flow?

Blood pressure increases blood flow

183

What is peripheral resistance?

The friction-like force decreasing blood flow along a vessel

184

How is peripheral resistance/flow measured

Pressure drop/ flow

185

How is blood flow increased during exercise?

Increase in blood pressure from profound decrease in resistance

186

Can an increase in blood pressure result from a decrease in peripheral resistance?

Yes. If there is an increase in venous return from the reduced peripheral resistance it can increase cardiac output and therefore blood pressure

187

What happens chemically during exercise?

Metabolic waste products cause local vasodilation
Hypoxia
Increased CO2
Sheer stress (NO)

188

How is blood pressure neurologically controlled?

ANS-Keeps systemic BP high
Sympathetic control

189

What are the centres in the brain responsible for controlling BP?

Vasomotor centre in medulla
Vasoconstrictor
Vasodilator
Cardioinhibtory

190

How do sympathetic nervous fibres work to control blood pressure?

Release noradrenaline (NA)
NA binds to a-receptors -> Vasoconstriction-> Increased peripheral resistance = Increased BP

191

How do sympathetic fibres (SNS) affect heart rate?

Increasing heart rate
Inotropic
Lusitropic

192

What does continuous constriction mean?

At rest there is underlying SNS though it can be turned off with anaesthesia

193

Where are arterial baroreceptors located?

Aortic arch
Carotid sinuses
Baroreflexes

194

How are carotid sinus baroreceptors stimulated?

Stretch - Signals transmitted to brain stem via afferent limbs of cranial nerve
Very sensitive

195

How do baroreflexes work to control blood pressure?

Cause increased/decreased sympathetic outflow -> constriction/ relaxation of pre-capillary sphincters

196

What happens to our blood flow when we stand up?

Fall in blood pressure
Vasoconstriction by SNS
Arteries increase in BP
Veins increase in venous return

197

Where can other arterial baroreceptors be found?

Low pressure receptors
Atrial stretch
Chemoreceptors
CNS Ischemia

198

Where would low pressure receptors be found?

In lower pressure part of circulation

199

What do atrial stretch receptors do?

Cause renal arteriolar dilation
Cause a decrease in ADH

200

How do chemoreceptors detect a decrease in blood pressure?

A decrease in PaO2

201

What is pressure diuresis?

Increased BP causes increased blood flow to kidneys -> increased urination and decreased BP

202

What happens to blood pressure when there is an increased salt and water uptake?

BP increases

203

How does kidney disease relate to BP?

A higher BP is required to remove the same amount of salt and water

204

What does RAAS stand for?

Renin Angiotensin Aldosterone System

205

What do the kidneys rely on to function that the heart produces?

High blood pressure

206

What happens in the kidneys if blood pressure decreases?

The juxtaglomerular apparatus releases renin

207

Is the RAAS system long term or short term? Why?

Long-term
Use of hormones

208

What does renin do after being released?

Converts angiotensinogen to angiotensin I (both are inactive)

209

What happens to angiotensin I after being produced?

It is converted to the active form - angiotensin II by ACE

210

What are the roles of angiotensin II?

Causes vasoconstriction, vascular hypertrophy and release of aldosterone

211

What receptors does angiotensin act on?

AT1 and AT2

212

What is the role of aldosterone?

Induces salt and water retention

213

How does increasing salt and water retention increase blood pressure?

Salt itself draws water towards it via osmosis.
Increasing water retention increased blood volume and therefore blood pressure.

214

Are there any other hormonal mechanisms for blood pressure control?

Natriuretic peptides
Arginine vasopressin

215

How do Natriuretic peptides control blood pressure?

Decrease in BP
They respond to stretch
Salt loss
Vasodilation

216

How does arginine vasopressin (ADH) control blood pressure?

Increase in BP
Vasoconstriction
Water retention

217

What do ACE inhibitor drugs usually end in?

-pril

218

What do angiotensin recepto blockers (ARBs) usually end in?

-sartan

219

What do antimineralcorticoids do?

Diuretic- Interfere with aldosterone by stopping it from retaining Na+ and water -> causes urination

220

What do alpha blockers generally do?

Block alpha receptors so noradrenaline can't bind
Decrease peripheral resistance and BP
Decrease heart rate

221

What do beta blockers generally do?

Bind to beta receptors so adrenaline and noradrenaline from SNS can't

222

What do calcium antagonists do?

Inhibit Ca2+ from entering smooth muscle cells.
This results in vasodilation because the smooth muscles in sphincters don't contract.

223

What do calcium antagonist drugs usually end in?

-ipine