Physiology Flashcards
(159 cards)
1
Q
What is meant by autorhythmicity of the heart?
A
It is able to generate its own electrical impulses without external stimuli
2
Q
Where does excitation of the heart normally originate?
A
SA node
3
Q
What are the specialised cells within the SA node that initiate the heart beat called?
A
Pacemaker cells
4
Q
What is meant by sinus rhythm?
A
Describes the heart’s pace being controlled by the SA node
5
Q
SA node cells have a stable resting membrane potential. True/False?
A
False
They exhibit spontaneous pacemaker potential
6
Q
What is the function of the spontaneous pacemaker potential?
A
Takes the membrane potential to threshold (depolarisation) to generate an action potential
7
Q
What gives rise to pacemaker potential?
A
Decrease in K+ efflux
Slow Na+ influx
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
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
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
11
Q
Which junctions allow cell-to-cell spread of excitation?
A
Gap junctions
12
Q
The AV node is the only point of electrical contact between atria and ventricles. True/False?
A
True
13
Q
AV node cells are large and slow to conduct. True/False?
A
False
They are small and slow to conduct
14
Q
Why is AV nodal delay present?
A
To allow time for atrial systole to precede ventricular systole
15
Q
Which fibres enable the excitation to spread to the ventricles?
A
Bundle of His and Purkinje fibres
16
Q
What gives rise to the rising phase of the action potential in ventricular contractile cells?
A
Fast Na+ influx
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
18
Q
Describe Phase 1 of the cardiac action potential
A
Closure of Na+ channels + transient K+ efflux causes some repolarisation
19
Q
What gives rise to the plateau phase (phase 2) of the cardiac action potential?
A
Ca++ influx
20
Q
What gives rise to the falling phase (phase 3) of the cardiac action potential?
A
K+ efflux
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
22
Q
Sympathetic stimulation causes increased heart rate. True/False?
A
True
23
Q
What is meant by vagal tone?
A
Parasympathetic stimulation to the heart dominating in resting conditions
24
Q
The vagus nerve supplies only the SA node. True/False?
A
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
What is contained within muscle fibres?
Myofibrils (contractile protein elements of muscle)
40
Actin filaments are thick and appear light. True/False?
False
They appear light but are thin
41
Myosin filaments are thick and appear dark. True/False?
True
42
What is the arrangement of of actin and myosin within each myofibril called?
Sarcomere
43
Myosin filaments slide over actin filaments to produce muscle tension. True/False?
False
Actin slides over myosin!
44
Where does the calcium that activates contractile machinery come from (where is it stored)?
Sarcoplasmic reticulum
45
What is meant by the refractory period?
Period following action potential where it is not possible to generate another action potential
46
What is the clinical benefit of the refractory period?
Prevents tetanic contractions of the heart
47
Define stroke volume
Volume of blood ejected by each ventricle per heart beat
EDV - ESV
48
What is meant by end diastolic volume (EDV)?
Volume of blood remaining in each ventricle following diastole
49
What determines EDV?
Venous return
50
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
51
What is meant by preload?
Volume of blood in each ventricle before contraction
52
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
53
What is meant by positive inotropic effect?
Force of contraction increases (due to sympathetic stimulation)
54
Parasympathetic system has a negative chronotropic and inotropic effect. True/False?
False
No inotropic effect
55
What does sympathetic stimulation do to the Frank-Starling curve?
Shifts it to the left (increased SV)
56
What is meant by cardiac output?
Volume of blood pumped out by each ventricle per minute
SV x HR
57
Cardiac valves produce a sound when they open and close. True/False?
False
Only produce a sound when they close (normally)
58
What is the cardiac cycle?
Encompasses all the events from one heartbeat to the next
59
What happens in Passive Filling?
AV valves open and blood flows into ventricles
60
80% of ventricular filling is done by atrial contraction. True/False?
False
80% is contributed to by passive filling
61
In Passive Filling, what are the pressures in the atria and ventricles?
Close to zero
62
What happens in Atrial Contraction?
Remaining atrial volume fills ventricles by atrial systole, completing the EDV
63
Which part of the ECG signals atrial depolarisation?
P wave
64
During which part of the ECG do the atria contract?
Between the P wave and QRS complex
65
Which part of the ECG signals ventricular depolarisation?
QRS complex
66
When does ventricular systole take place on the ECG?
Between end of QRS and beginning of T wave (ST segment)
67
What produces the dicrotic notch in the aortic pressure curve?
Aortic valve closing
68
S1 heralds the end of systole. True/False?
False
Heralds the start of systole (AV valves shut)
69
S2 heralds the start of diastole. True/False?
True
70
Define 'blood pressure'
Outward force exerted by blood on blood vessel walls
71
Which sort of blood flow can be heard through a stethoscope?
Turbulent
72
What is the 1st Korotkoff sound?
Peak systolic pressure
73
What are the 2nd-3rd Korotkoff sounds?
Intermittent sounds of turbulent flow
74
What is the 4th Korotkoff sound?
Last muffled sound heard before sound stops
75
What is the 5th Korotkoff sound?
No sound!
Represents diastolic pressure
76
What are the formulae for calculating MAP?
[2 x diastolic + systolic]/3
diastolic + [systolic - diastolic]/3
CO x TPR
SV x HR x TPR
77
What is the normal range for MAP?
70-105 mm Hg
78
MAP of at least 50 mm Hg is needed to perfuse the vital organs. True/False?
False
At least 60 mm Hg is needed
79
Arteries are the main resistance vessels. True/False?
False
80
What are the main resistance vessels?
Arterioles
81
Which receptors regulate blood pressure short-term?
Baroreceptors
82
The higher the blood pressure, the greater the firing of baroreceptors. True/False?
True
83
Which CN do the carotid baroreceptors fire through?
CN IX
84
Which CN do the aortic baroreceptors fire through?
CN X
85
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
86
When you suddenly stand up, what happens to the venous return to the heart and thus MAP?
Decreases
87
How much of total body fluid does extracellular fluid contribute to?
1/3
88
What is the function of renin in the RAAS?
Released from kidneys to stimulate conversion of angiotensinogen to angiotensin I
89
What is the function of ACE?
Converts angiotensin I to angiotensin II
90
What is the function of angiotensin II?
Stimulates release of aldosterone
Causes systemic vasoconstriction
91
What is the function of aldosterone in the RAAS?
Acts on kidneys to increase Na+ and water retention
92
Where is renin released from?
Juxtapulmonary apparatus in the kidney
93
Renal artery hypertension causes renin to be released. True/False?
False
Hypotension would cause its release
94
Where is ANP stored?
Atrial myocytes
95
What does ANP do?
Causes excretion of Na+ and water in the kidneys
Vasodilates
Decreases renin release
[counteracts RAAS]
96
When is ADH release stimulation?
Reduced extracellular fluid
Increased extracellular fluid osmolarity (solute)
97
What does ADH do?
Causes reabsorption of water, i.e. concentrates urine, to increase plasma volume
Vasoconstriction (small degree)
98
Which blood vessel holds the most blood volume at rest?
Veins
99
Resistance to blood flow is directly proportional to what?
Thickness and length of blood vessel
100
Resistance to blood flow is inversely proportional to what?
[Radius of blood vessel]^4
101
How is resistance to blood flow mainly controlled?
Through changes in the radius of the vessel
102
What is meant by vasomotor tone?
Vascular smooth muscle being partially constricted at rest due to tonic discharge of the sympathetic system (releases noradrenaline)
103
There is no parasympathetic innervation of vascular smooth muscle. True/False?
False
There is in the penis and clitoris
104
Adrenaline acting on alpha receptors causes what?
Vasoconstriction
105
Adrenaline acting on beta receptors causes what?
Vasodilation
106
What is the effect of angiotensin II on vascular smooth muscle?
Vasoconstriction
107
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
108
Decreased local PO2 causes vasoconstriction in systemic circulation. True/False?
False
Causes vasodilation
109
What is the effect of decrease in local PO2 in pulmonary circulation arterial smooth muscle?
Vasoconstriction
110
Increased local [H+] and [K+] in systemic circulation causes vasodilation. True/False?
True
111
Name some humoral agents that are potent vasodilators
Histamine
Bradykinin
Prostaglandins
Nitric oxide
112
Name some humoral agents that are potent vasoconstrictors
Serotonin
Thromboxane A2
Leukotrienes
Endothelin
113
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)
114
Sympathetic stimulation increases during exercise. What does this do to the HR, SV and CO?
Increases all of them
115
How does blood flow change to the kidney and gut during exercise?
Decreases - vasomotor tone causes vasoconstriction in these areas
116
How does blood flow change to skeletal and cardiac muscle during exercise?
Increases due to vasodilation in these areas
117
What causes vasodilation in skeletal and cardiac muscle during exercise? i.e. what overrides sympathetic effects?
Metabolic hyperraemia
118
Systolic and diastolic murmurs coincide with the carotid pulse. True/False?
False
Only systolic murmurs coincide with carotid pulse
119
Physiological splitting of the 2nd heart sound occurs on inspiration. True/False?
True
120
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)
121
A 4th heart sound is always pathological. True/False?
True
122
Define 'shock'
An abnormality in the circulatory system, resulting in inadequate tissue perfusion and oxygenation
123
Which 3 factors influence the stroke volume?
Preload (venous return)
Myocardial contractility
Afterload
124
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
125
How does cardiogenic shock arise?
Decreased myocardial contractility leads to decreased stroke volume leads to decreased CO + BP = low perfusion and oxygenation
126
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
127
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
128
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
129
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
130
What are the first branches/arteries that come off the aorta?
Right + left coronary arteries
131
What drains coronary venous blood into the right atrium?
Coronary sinus
132
Which organ has the greatest oxygen demand?
The heart
133
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
134
How is the oxygen supply to the heart increased, if not by increasing oxygen extraction?
Increase coronary blood flow
135
Decreased PO2 causes coronary vasoconstriction. True/False?
False
Need to improve oxygenation, therefore vasodilation occurs to increase blood flow
136
Decreased PO2 causes pulmonary vasoconstriction. True/False?
True
137
What effect do K+, H+ and CO2 have on coronary arteries?
Vasodilation
138
When does peak coronary flow occur?
Diastole
139
Which arteries supply the brain?
Internal carotid arteries
Vertebral arteries
140
Which brain matter - grey or white - is very sensitive to hypoxia?
Grey matter
141
Which arteries make up the Circle of Willis?
Internal carotids + basilar artery (formed by both vertebral arteries joining)
142
The baroreceptor reflex affects the brain. True/False?
False
143
If MAP rises, cerebral vessels constrict. True/False?
True
144
If MAP falls, cerebral vessels dilate. True/False?
True
145
When does autoregulation of cerebral blood flow fail?
When MAP is less than 60 or greater than 160 mm Hg
146
Decreased PCO2 results in cerebral vasodilation. True/False?
False
Results in vasoconstriction - this is why hyperventilation leads to fainting
147
Head injury and tumours increase intracranial pressure. How does this affect cerebral blood flow?
Decreases it
148
Decreased O2 does what to pulmonary arterioles? Why?
Vasoconstriction (opposite to systemic circulation)
Redirects blood to alveoli to get more oxygen
149
2/3 of body water is extracellular. True/False?
False
2/3 is intracellular
150
What is the function of capillaries?
Rapid exchange of gases, water and solutes with the interstitial fluid
151
Forces favouring absorption are stronger at the venule end. True/False?
True
152
What are the forces favouring filtration?
Capillary hydrostatic pressure (Pc)
Interstitial fluid osmotic pressure (πi)
153
What are the forces favouring absorption?
Capillary osmotic pressure (πc)
Interstitial fluid hydrostatic pressure (Pi)
154
What is the main contributor to capillary hydrostatic pressure (Pc)?
Blood flow
Tends to force blood out of capillary
155
What is the main contibutor to capillary osmotic pressure (πc)?
Presence of plasma proteins
Tends to force blood into capillary
156
How is net filtration pressure calculated using forces described previously?
(Pc + πi) - (πc - Pi)
157
What is oedema? How does it affect diffusion?
Accumulation of fluid in the interstitial space
Increases distance over which diffusion must take place
158
LV failure causes pulmonary oedema. True/False?
True
159
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
