Week 6 Formative Quiz questions

Question 1

Regarding control of the peripheral circulation: Circulating adrenaline causes arteriolar constriction in all body regions.

Answer 1

False. Whilst adrenaline activates alpha 1 receptors and causes arteriolar constriction in the vast majority of body regions, there are notable exceptions. These are the skeletal muscle and cardiac muscle which also express beta 2 receptors which cause arteriolar dilation and swamp the alpha 1 receptor mediated constriction.

Question 2

Concerning the cardiac cycle: At resting heart rate, systole takes approximately twice as long as diastole.

Answer 2

False. At resting heart rate, systole takes about 1/3rd of the cardiac cycle, ie it is half as long as diastole. At higher heart rates, most of the time is taken out of diastole and so systole takes a proportionally greater proportion of the cycle.

Question 3

Concerning the electrical activity of the heart: Cells of the myocardium are electrically connected via gap junctions.

Answer 3

True. Cells of the myocardium are both electrically connected (via gap junctions) and physically connected (via the desmosomes). Hence it acts as functional syncytium which depolarizes as one, and contracts as one.

Question 4

Concerning the electrical activity of the heart: A gradual opening of leaky K+ channels contributes to the pacemaker potential.

Answer 4

False. A gradual closing of K+ channels is one of the factors that contributes to the pacemaker potentials – the others being opening of the “funny” Na+ channels and T-type Ca2+ channels. Gradual opening of K+ channels would hyperpolarize the cell.

Question 5

Concerning the cardiac cycle: The left atrial pressure rises at the start of systole.

Answer 5

True. When the ventricle contacts, the mitral and tricuspid valves close and then bulge into the atria, creating the a wave on the atrial pressure trace, which terminates when the aortic and pulmonary valves open.

Question 6

Concerning the cardiovascular system: Mean arterial pressure (MAP) is calculated by measuring the pressure in all the arteries of the systemic circulation and taking the average.

Answer 6

False. Pressure in all systemic arteries is approximately the same. The mean arterial pressure describes the average pressure in the arteries throughout the cardiac cycle. This is approximately equal to the diastolic pressure plus a third of the pulse pressure.

Question 7

Concerning the vascular system: Most arterioles are innervated only by parasympathetic nerves.

Answer 7

False. Most blood vessels are innervated only by sympathetic vessels. These release noradrenaline which activates alpha 1 receptors and causes vasoconstriction. Most vessels are not innervated by the parasympathetic system. The genitalia and salivary glands are the exceptions that prove the rule.

Question 8

Concerning the cardiac cycle: The stroke volume of the right ventricle is approximately one fifth of that of the left ventricle.

Answer 8

False. The right and left sides of the heart lie in series and must have the same cardiac output or blood will accumulate in the systemic or pulmonary circulations. They have the same heart rate because they share the same pacemaker, so the stroke volume must also be the same. If you got it wrong you were probably thinking of the pressure evoked by the left ventricle, which is about one fifth of that of the left.

Question 9

Concerning the vascular system: Local arteriolar dilation, as occurs in exercising muscle, may cause oedema.

Answer 9

True. Arteriolar dilation will increase the hydrostatic pressure in downstream capillaries and increase the amount of fluid that is filtered out through Starling’s forces.

Question 10

Concerning the electrical activity of the heart: The PR interval gives a good indication of the time taken for the spread of depolarisation across the atria.

Answer 10

False. The PR interval indicates the time between the start of atrial depolarization and the start of ventricular depolarization. This includes the time for depolrisation to spread across the atria, but it is mostly due to the slow conduction through the atrioventricular node.

Question 11

Concerning the pumping ability of the heart: Stimulation of sympathetic fibres innervating the heart increases contractility.

Answer 11

True. Noradrenaline acting on beta1 receptors increases excitation-contraction coupling and gives a stronger contraction for any given preload.

Question 12

Concerning the cardiac cycle: End systolic volume of the ventricle is approximately 0ml.

Answer 12

False. End systolic volume will vary from person to person but is likely to be closer to 60ml. If end systolic volume was 0ml, increased strength of contraction could not increase stroke volume.

Question 13

Concerning the cardiac cycle: The second heart sound is caused by closure of the aortic and pulmonary valves

Answer 13

True. The normal heart sounds are caused by turbulence in the blood as the mitral and tricuscpid, and then the aortic an pulmonary valves close.

Question 14

Concerning the electrical activity of the heart: The plateau phase of the cardiac action potential is maintained by entry of Na+ ions.

Answer 14

False. The initial fast depolarising phase of the non-pacemaker potential is mediated by voltage gated Na+ channels, but the plateau phase is mediated by L-type voltage gated Ca2+ channels.

Question 15

Concerning the electrical activity of the heart: The QRS complex immediately precedes ventricular contraction.

Answer 15

True. The QRS complex is created by the wave of depolarization spreading through the ventricle, which in turn triggers ventricular contraction.

Question 16

Concerning the cardiac cycle: The left ventricular pressure is approximately 80 mmHg during diastole.

Answer 16

False. During diastole (the filling phase), the pressure in the left ventricle is very low – maybe even 0mmHg.

Question 17

Concerning the electrical activity of the heart: The Q-T interval gives a rough indication of the duration of ventricular systole.

Answer 17

True. The Q-T interval indicates the time between ventricular depolarisation and ventricular repolarisation, ie the length of the ventricular action potential. This is approximately the same as the length of the contraction evoked and therefore the duration of systole.

Question 18

Regarding control of the peripheral circulation: Increasing the radius of an arteriole 2-fold, increases its resistance 16-fold.

Answer 18

False. Close. Varying radius does alter resistance to the power of 4, but increasing radius will reduce resistance, not increase it.

Question 19

Concerning the cardiac cycle: The aortic valve is closed throughout diastole.

Answer 19

True. It prevents the flow of blood back in from the high pressure aorta during the ventricular filling phase.

Question 20

Concerning the electrical activity of the heart: Hyperkalemia (a high concentration of K+ in the plasma) is liable to cause fibrillation of the myocardium.

Answer 20

True. Hyperkalemia will depolarise myocardial cells so that they approach threshold and randomly fire action potentials and contract rather than waiting for appropriate depolarization via the special conducting system.

Question 21

Concerning the vascular system: The major resistance to blood flow is produced by the arteries.

Answer 21

False. The arteries have a wide lumen and therefore a low resistance. The major resistance is created by the arterioles with their relatively narrow lumen and thick contractile wall.

Question 22

The T-wave of the ECG is positive going in standard limb lead II because the action potential in endocardial cells is longer than the action potential in epicardial cells.

Answer 22

True. This explains why the main vector of depolarisation spreads down the ventricle, but the main vector of repolarization spreads in the opposite direction.

Question 23

Regarding control of the peripheral circulation: Metabolic autoregulation is a mechanism which matches the metabolic rate of a body region to its energy reserves.

Answer 23

False. Metabolic autoregulation is a mechanism that matches the blood flow of a body region to its metabolic demands.

Question 24

Concerning the vascular system: Rhythmic contraction of skeletal muscle promotes venous return.

Answer 24

True. This the action of the skeletal muscle pump. It is one of several mechanism that increase venous pressure and venous return during exercise and therefore offset the reduction in end diastolic volume caused by heart heart rates. The others include the respiratory pump, venomotor tone, and increased systemic filling pressure.

Question 25

Concerning the electrical activity of the heart: The refractory period of the action potential is much shorter than the contraction it produces.

Answer 25

False. Unlike skeletal muscle, because of its long action potential the refractory period of cardiac muscle is almost as long as the twitch contraction it evokes. The result is that the cardiac muscle must relax before it can contract again. It cannot exhibit a tetanic contraction.

Question 26

Concerning the vascular system: Blood velocity is lowest in the capillaries.

Answer 26

True. Blood velocity is related to total cross-sectional area of the vessels. The aorta has a low total cross-sectional area and the blood velocity must therefore be very fast. The total cross-sectional area of the capillaries is massive and velocity of blood flow through them is therefore very slow.

Question 27

Concerning the pumping ability of the heart: Cutting the sympathetic and parasympathetic innervation of the sinoatrial node will cause an increase in resting heart rate.

Answer 27

True. The fastest (and therefore the) pacemaker cells of the heart have an inherent rate of about 100 beats per minute. This can be speeded up by the sympathetic system or slowed down by the parasympathetic system. At rest, the parasympathetic system dominates and so the heart is said to be under vagal restraint, giving the resting heart rate of about 70 beats per minute.

Question 28

Concerning the cardiac cycle: The first heart sound is caused by opening of the mitral and tricuspid valves.

Answer 28

False. Opening of the valves does not evoke any heart sounds in health.

Question 29

Concerning the vascular system: A low concentration of protein in the blood (hypoproteinemia) may cause oedema.

Answer 29

True. In the periphery water is lost from the capillaries through the hydrostatic pressure gradient. This creates an osmotic gradient in the opposite direction which draws water back into the capillary. If the concentration of protein in the plasma is low, this osmotic gradient cannot develop and so less fluid is re-absorbed.

Question 30

Concerning the cardiac cycle: The second heart sound is heard at the start of diastole.

Answer 30

True. The first heart sounds is caused by the mitral and tricuscpid valves closing at the start of systole, and the second is caused by the aortic and pulmonary valves closing at the start of diastole

Question 31

Regarding control of the peripheral circulation: The injury response depends on intact nociceptive nerve function.

Answer 31

True. The injury response depends on action potentials invading the terminals of nociceptive C-fibres and triggering the release of substance P.

Question 32

Concerning the cardiac cycle: A systolic murmur could be caused by regurgitation of blood through the aortic valve.

Answer 32

False. A murmur is generally caused by turbulence in the blood due to regurgitation through a valve that should be closed, or stenosis (narrowing) of a valve that should be open. During systole the aortic valve is open so a systolic murmur could be due to stenosis of the aortic valve. Regurgitation through the aortic valve would cause a diastolic murmur.

Question 33

Regarding control of the peripheral circulation: Smooth muscle in the walls of capillaries controls their blood flow by constriction and relaxation to vary resistance.

Answer 33

False. The capillaries have no smooth muscle and cannot vary their resistance. Instead it is the job of the upstream arterioles (the resistance vessels) to control blood flow.

Question 34

Concerning the pumping ability of the heart: Increased venous return causes an increased stroke volume.

Answer 34

True. In vivo, increased venous return during the filling phase increases end diastolic volume which increases preload on the heart. Starling’s law tells you that this will cause an increased strength of contraction and therefore increases stroke volume.

Question 35

Concerning the arterial baroreflex: Sensory information from the arterial baroreceptors is primarily concerned with regulation of mean arterial pressure in the short, rather than the long, term.

Answer 35

True. Cutting the sensory nerves from the aortic and arch and carotid sinus baroreceptors results in loss of short-term, but not long-term, control of blood pressure. Long term control of blood pressure may rely more on sensory input from the cardiopulmonary baroreceptors.

Question 36

Concerning the cardiovascular system: Cardiac output at rest is approximately 75ml/beat.

Answer 36

False. 1. This is a good figure for the stroke volume, but the cardiac output is the volume of blood pumped out per minute. This is likely to be about 5 litres per min.

Question 37

Concerning the cardiovascular system: The circular smooth muscle of arterioles controls peripheral resistance under the influence of the sympathetic nervous systems

Answer 37

True. The arterioles are indeed the resistance vessels. The smooth muscle surrounding them is controlled by intrinsic mechanisms, but also by central mechanisms. Notably the sympathetic nerves which innervate the arterioles and release noradrenaline, and adrenaline which is released from the adrenal medulla. Both of these activate alpha 1 receptors on the smooth muscle which causes arteriolar constriction and regulates peripheral resistance.

Question 38

Concerning the vascular system: Most vascular beds are arranged in parallel.

Answer 38

True. The significance of this being that all body regions receive fresh oxygenated blood, and that the cardiac output can be redirected between different body regions when required.

Question 39

The PR interval is normally under 0.2 seconds.

Answer 39

True. The PR interval represents the time between the start of atrial depolarization and the start of ventricular depolarisation. Most of this is taken up by conduction through the atrio-ventricular node. An interval of over 0.2 seconds indicates that this is impaired and is classed as 1st degree heart block.

Question 40

Concerning the arterial baroreflex: A fall in baroreceptor firing rate triggers a reflex increase in sympathetic outflow.

Answer 40

True. A fall in baroreceptor firing rate signals a fall in mean arterial pressure which triggers (amongst other things) an increase in sympathetic outflow. This will increase heart rate, increase stroke volume, cause venoconstriction and cause arteriolar constriction, all of which will contribute a pressor response - ie an increase in blood pressure.

Question 41

Concerning the cardiovascular system: The mean arterial pressure (MAP) in the aorta is approximately equal to the mean arterial pressure in the pulmonary trunk.

Answer 41

False. The pressure evoked in the pulmonary circulation by the right side of the heart is about 1/5th of that evoked in the systemic circulation by the left side of the heart.

Question 42

Concerning the cardiovascular system: MAP = CO x TPR

Answer 42

True. Another way of looking at this is that the pressure in the arteries is affected by how much blood is pushed into them (the cardiac output), and how easy it is for the blood to get out (the total peripheral resistance). This is also referred to as the fundamental equation of cardiovascular physiology because the body spends so much time monitoring MAP and adjusting CO and TPR accordingly.

Question 43

Concerning the cardiac cycle: Most of the stroke volume leaves the ventricle during the first third of systole.

Answer 43

True. This is the rapid ejection phase.

Question 44

Concerning the electrical activity of the heart: Cardiac contraction is initiated by sympathetic nerves.

Answer 44

False. The heart has its own inherent rhythm that is normally set by the pacemaker cells in the sinoatrial node. It can be slowed down by the parasympathetic system and speeded up by the sympathetic system, but it does not rely on these to initiate the heart beat.

Question 45

Concerning the electrical activity of the heart: The atrioventricular node is the only electrically conducting region connecting the atria and the ventricles.

Answer 45

True. The atria and the ventricles are separated by the non-conducting annulus fibrosus, except for the very slow-conducting atrioventricular node.

Question 46

Concerning the vascular system: The smooth muscle surrounding the arterioles of the coronary circulation expresses beta 2 receptors.

Answer 46

True. The heart and skeletal muscle are two locations in which the smooth muscle surrounding arterioles expresses many beta 2 receptors. These are coupled to second messenger pathways that relax the smooth muscle and therefore cause arteriolar dilation. This increases blood flow and contributes to the redirection of blood flow to these areas during exercise.

Question 47

Concerning the electrical activity of the heart: The fastest depolarising pacemaker potentials in the heart are usually found in the cells of the sinoatrial node.

Answer 47

True. Many myocardial cells show some pacemaker activity, but the fastest pacemakers will set the rate for all the rest, and these are normally in the sino-atrial node.

Question 48

Regarding control of the peripheral circulation: Arterioles in most organs constrict in response to local hypoxia.

Answer 48

False. In most body regions, hypoxia is taken as a sign that that region needs more blood and so causes arteriolar dilation. The pulmonary circulation is the exception, where blood is redirected to the better ventilated parts of the lung which maximises ventilation-perfusion matching.

Question 49

Regarding control of the peripheral circulation: The endothelium has an important role in the control of the peripheral circulation.

Answer 49

True. Endothelial cells have a key role in sensing metabolite concentrations and releasing autocrine agents such as EDRF (NO) to enable the intrinsic control of blood flow in a vascular bed.

Question 50

Concerning the arterial baroreflex: Rising from a sitting to a standing position will cause a reflex increase in heart rate and total peripheral resistance.

Answer 50

True. But do you understand the mechanism? Standing causes pooling of blood in the venules of the feet and legs. This reduces end diastolic volume and therefore preload, stroke volume, cardiac output and mean arterial pressure. This fall in blood pressure is sensed by the arterial baroreceptors which trigger a reflex increase in, amongst other things, heart rate and total peripheral resistance to restore blood pressure.

Question 51

Regarding control of the peripheral circulation: Increasing the radius of an arteriole 2-fold, increases its resistance 16-fold.

Answer 51

False. Close. Varying radius does alter resistance to the power of 4, but increasing radius will reduce resistance, not increase it.

Question 52

Concerning the electrical activity of the heart: Hyperkalemia (a high concentration of K+ in the plasma) is liable to cause fibrillation of the myocardium.

Answer 52

True. Hyperkalemia will depolarise myocardial cells so that they approach threshold and randomly fire action potentials and contract rather than waiting for appropriate depolarization via the special conducting system.

Question 53

Concerning the cardiac cycle: The second heart sound is caused by closure of the aortic and pulmonary valves

Answer 53

True. The normal heart sounds are caused by turbulence in the blood as the mitral and tricuscpid, and then the aortic an pulmonary valves close.

Question 54

Concerning the vascular system: A low concentration of protein in the blood (hypoproteinemia) may cause oedema.

Answer 54

True. In the periphery water is lost from the capillaries through the hydrostatic pressure gradient. This creates an osmotic gradient in the opposite direction which draws water back into the capillary. If the concentration of protein in the plasma is low, this osmotic gradient cannot develop and so less fluid is re-absorbed.

Question 55

Concerning the arterial baroreflex: A fall in baroreceptor firing rate triggers a reflex increase in sympathetic outflow.

Answer 55

True. A fall in baroreceptor firing rate signals a fall in mean arterial pressure which triggers (amongst other things) an increase in sympathetic outflow. This will increase heart rate, increase stroke volume, cause venoconstriction and cause arteriolar constriction, all of which will contribute a pressor response - ie an increase in blood pressure.

Question 56

Concerning the cardiac cycle: End systolic volume of the ventricle is approximately 0ml.

Answer 56

False. End systolic volume will vary from person to person but is likely to be closer to 60ml. If end systolic volume was 0ml, increased strength of contraction could not increase stroke volume.

Question 57

Concerning the cardiovascular system: Cardiac output at rest is approximately 75ml/beat.

Answer 57

False. 1. This is a good figure for the stroke volume, but the cardiac output is the volume of blood pumped out per minute. This is likely to be about 5 litres per min.

Question 58

Concerning the cardiac cycle: The second heart sound is heard at the start of diastole.

Answer 58

True. The first heart sounds is caused by the mitral and tricuscpid valves closing at the start of systole, and the second is caused by the aortic and pulmonary valves closing at the start of diastole

Question 59

Concerning the electrical activity of the heart: A gradual opening of leaky K+ channels contributes to the pacemaker potential.

Answer 59

False. A gradual closing of K+ channels is one of the factors that contributes to the pacemaker potentials – the others being opening of the “funny” Na+ channels and T-type Ca2+ channels. Gradual opening of K+ channels would hyperpolarize the cell.

Question 60

The T-wave of the ECG is positive going in standard limb lead II because the action potential in endocardial cells is longer than the action potential in epicardial cells.

Answer 60

True. This explains why the main vector of depolarisation spreads down the ventricle, but the main vector of repolarization spreads in the opposite direction.