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
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
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
