Week 6 Formative Quiz questions Flashcards
Regarding control of the peripheral circulation: Circulating adrenaline causes arteriolar constriction in all body regions.
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.
Concerning the cardiac cycle: At resting heart rate, systole takes approximately twice as long as diastole.
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.
Concerning the electrical activity of the heart: Cells of the myocardium are electrically connected via gap junctions.
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.
Concerning the electrical activity of the heart: A gradual opening of leaky K+ channels contributes to the pacemaker potential.
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.
Concerning the cardiac cycle: The left atrial pressure rises at the start of systole.
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.
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.
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.
Concerning the vascular system: Most arterioles are innervated only by parasympathetic nerves.
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.
Concerning the cardiac cycle: The stroke volume of the right ventricle is approximately one fifth of that of the left ventricle.
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.
Concerning the vascular system: Local arteriolar dilation, as occurs in exercising muscle, may cause oedema.
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.
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.
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.
Concerning the pumping ability of the heart: Stimulation of sympathetic fibres innervating the heart increases contractility.
True. Noradrenaline acting on beta1 receptors increases excitation-contraction coupling and gives a stronger contraction for any given preload.
Concerning the cardiac cycle: End systolic volume of the ventricle is approximately 0ml.
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.
Concerning the cardiac cycle: The second heart sound is caused by closure of the aortic and pulmonary valves
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.
Concerning the electrical activity of the heart: The plateau phase of the cardiac action potential is maintained by entry of Na+ ions.
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.
Concerning the electrical activity of the heart: The QRS complex immediately precedes ventricular contraction.
True. The QRS complex is created by the wave of depolarization spreading through the ventricle, which in turn triggers ventricular contraction.
Concerning the cardiac cycle: The left ventricular pressure is approximately 80 mmHg during diastole.
False. During diastole (the filling phase), the pressure in the left ventricle is very low – maybe even 0mmHg.
Concerning the electrical activity of the heart: The Q-T interval gives a rough indication of the duration of ventricular systole.
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.
Regarding control of the peripheral circulation: Increasing the radius of an arteriole 2-fold, increases its resistance 16-fold.
False. Close. Varying radius does alter resistance to the power of 4, but increasing radius will reduce resistance, not increase it.
Concerning the cardiac cycle: The aortic valve is closed throughout diastole.
True. It prevents the flow of blood back in from the high pressure aorta during the ventricular filling phase.
Concerning the electrical activity of the heart: Hyperkalemia (a high concentration of K+ in the plasma) is liable to cause fibrillation of the myocardium.
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.
Concerning the vascular system: The major resistance to blood flow is produced by the arteries.
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.
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.
True. This explains why the main vector of depolarisation spreads down the ventricle, but the main vector of repolarization spreads in the opposite direction.
Regarding control of the peripheral circulation: Metabolic autoregulation is a mechanism which matches the metabolic rate of a body region to its energy reserves.
False. Metabolic autoregulation is a mechanism that matches the blood flow of a body region to its metabolic demands.
Concerning the vascular system: Rhythmic contraction of skeletal muscle promotes venous return.
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.