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PHSL2101
Final exam
47
Physiology
Undergraduate 2
06/05/2016

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Term
Which ONE of the following is responsible for the rapid depolarization phase of an action potential within the pacemaker cells?
A. An increase in PCa2+
B. An increase in PK+
C. A decrease in PK+
D. An increase in PNa+
E. A decrease in PNa+
Definition
Answer: A.

An increase in PCa2+ allows Ca to flow into the cell causing the rapid depolarization phase of an action potential within the pacemaker cells.
Term
Which ONE of the following statements regarding blood vessels is INCORRECT?
A. Veins function as volume reservoirs due to their high compliance.
B. The pressure in venules would be less than the pressure in large veins.
C. Capillaries are the vessel type that have the greatest total surface area.
D. The elastic nature of the walls of arteries allows them to act as a pressure reservoir.
E. The contractile activity of smooth muscle cells within arterioles is primarily involved in the control of organ blood flow.
Definition
Answer: B.

The pressure in the large veins is lower than the pressure in the venules.
Term
A reflex increase in heart rate may be caused by:
A. a decrease in arterial blood pressure.
B. an increase in right atrial pressure.
C. a decrease in peripheral resistance.
D. an increase in venous return.
E. all of the above.
Definition
Answer: E.

Increased right atrial pressure is usually a result of increased venous return and would activate low-pressure baroreceptors or volume receptors in the atrial wall, which would increase heart rate. Decreased arterial blood pressure (also the result of a decrease in peripheral resistance) would activate high-pressure baroreceptors in the aortic arch and carotid bodies, also causing a reflex increase in heart rate.
Term
The greatest proportion of blood volume is present within which ONE of the following vessel types?
A. Systemic capillaries
B. Pulmonary blood vessels
C. Systemic veins and venules
D. Heart
E. Systemic arteries and arterioles
Definition
Answer: C.

The venules and veins contain about 60% of the total blood volume.
Term
The major mechanism controlling the diameter of arteries in the skin is:
A. sympathetic nerve activity
B. extracellular CO2 concentration
C. myogenic
D. extracellular K+ concentration
E. accumulation of metabolic waste products
Definition
Answer: A.

Sympathetic nerve activity is the most important controller of blood flow in the skin.
Term
Closure of the aortic valve is associated with all of the following except:
A. rapid filling of the left ventricle.
B. dicrotic notch on the aortic pressure wave.
C. relaxation of the ventricle.
D. the second heart sound.
E. T-wave of the ECG.
Definition
Answer: A.

Closure of the aortic valve is not associated with rapid filling of the left ventricle. Rapid filling of the left ventricle occurs some time after the aortic valve has closed.
Term
According to Fick’s law, which ONE of the following would NOT be a factor in diffusion of a substance across the capillary wall?
A. The plasma concentration of the substance
B. Hydrostatic (blood) pressure in the capillary
C. The total surface area of the capillary wall
D. The molecular weight of the substance
E. The concentration of the substance in the interstitial fluid
Definition
Answer: B.

Hydrostatic pressure in capillaries is important in controlling filtration or absorption of water from or into capillaries, but has no role in determining diffusion of solutes as defined by Fick’s Law (J=-PS(Co-Ci)).
Term
In cardiac muscle, the action potential in the ventricles:
A. has an unstable resting membrane potential.
B. is shorter than the action potential of a pacemaker cell.
C. has a resting membrane potential of about -60mV.
D. is due to an increase in chloride permeability.
E. relies on an increase in calcium permeability.
Definition
Answer: E.

An increase in calcium permeability is responsible for the plateau phase of this action potential.
Term
Which ONE of the following statements about an action potential generated from a non-pacemaker cardiac cell is INCORRECT?
A. Repolarisation occurs as a result of inactivation of K+ channels.
B. The plateau phase of the action potential is associated with a prolonged increase in Ca2+permeability.
C. The refractory period in ventricular muscle corresponds approximately to the plateau phase of the action potential.
D. The resting membrane potential depends to a great extent on the permeability of the cell membrane to K+.
E. Depolarisation is initiated by rapid entry of Na+.
Definition
Answer: A.

This is the incorrect statement. Repolarisation occurs as a result of activation (not inactivation) of K+ channels.
Term
Pre-load is equivalent to
A. Peak ejection pressure
B. Stroke volume
C. Ventricular end-diastolic volume (EDV)
D. Right atrial pressure
E. Ventricular end-systolic volume (ESV)
Definition
Answer: C.

Pre-load is the degree to which the ventricular muscle fibres are stretched prior to contraction, and the degree of stretch is determined by the amount of blood in the ventricle at the end of the filling phase, which is the end of diastole, the end-diastolic volume.
Term
Unlike blood vessels, the lymphatic system:
A. removes damaged erythrocytes from the circulation.
B. has a role in controlling blood pressure.
C. reabsorbs protein and foreign particles from the interstitial fluid.
D. forms a filtrate which eventually becomes urine.
E. can generate local vasoactive substances.
Definition
Answer: C.
Term
Compared to sinoatrial cells, ventricular contractile cells will have:
A. A more negative resting membrane potential
B. A smaller amplitude action potential
C. An action potential with a shorter duration
D. A slower conduction velocity
E. A slower depolarisation during the action potential
Definition
Answer: A.

Ventricular cells have a much more negative resting membrane potential than sinoatrial cells.
Term
Which ONE choice indicates three events that occur at about the same time during the cardiac cycle?
A. A-V valve closure, second heart sound, ventricular diastole.
B. semilunar valve closure, second heart sound, ventricular systole.
C. A-V valve closure, first heart sound, ventricular systole.
D. A-V valve closure, first heart sound, ventricular diastole.
E. semilunar valve closure, first heart sound, ventricular diastole.
Definition
Answer: C.

At the beginning of ventricular systole, the AV valve closes generating the first heart sound.
Term
Which ONE of the following parameters, when increased, will cause an increase in cardiac stroke volume?
A. peripheral resistance
B. blood pressure
C. afterload
D. end-systolic volume (ESV)
E. end-diastolic volume (EDV)
Definition
Answer: E.

Stroke volume = end-diastolic volume - end systolic volume. So if end-diastolic volume is increased, stroke volume would increase.
Term
The decrease in blood pressure is greatest across ______ because this is where ______ is highest.
A. capillaries, cross-sectional area
B. capillaries, resistance
C. veins, cross-sectional area
D. arterioles, resistance
E. aorta, cross-sectional area
Definition
Answer: D.

Resistance  =  Pressure Gradient / Flow. Resistance to flow is highest in arterioles, and this is where the greatest decrease in blood pressure occurs (from 80 to about 30 mmHg).
Term
Cardiac stroke volume may be defined as
A. end-systolic volume (ESV) minus end-diastolic volume (EDV)
B. afterload minus pre-load
C. end-diastolic volume (EDV) minus end-systolic volume (ESV)
D. peak ejection pressure minus diastolic pressure
E. pre-load minus afterload
Definition
Answer: C.
Term
Which ONE of the following would NOT result in an increase in the movement of fluid out of capillaries?
A. An increase in blood pressure within the capillary.
B. A decrease in colloid osmotic pressure of the plasma.
C. A decrease in the osmotic pressure of the interstitial fluid
D. A decrease in interstitial fluid pressure
E. None of the above
Definition
Answer: C

Using Starling’s equation,
Jv = k[(Pc + πif)-(Pif + πp)],  a decrease in the osmotic pressure of the interstitial fluid (πif), would decrease outward fluid movement from the plasma.
Term
If systemic blood pressure falls, the carotid baroreceptors would cause heart rate to ______ and peripheral ________.

A. Stay the same, vasoconstriction
B. Increase, vasodilation
C. Decrease, vasoconstriction
D. Decrease, vasodilation
E. Increase, vasoconstriction
Definition
Answer: E.

If blood pressure falls, baroreceptors would act to increase blood pressure. Increased heart rate would increase cardiac output (CO) and peripheral vasoconstriction would increase total peripheral resistance (TPR). As blood pressure = CO x TPR, these actions would increase blood pressure.
Term
Stimulation of the heart by sympathetic nerves
A. causes tachycardia
B. results in inhibition the baroreceptor reflex
C. has no effect on cardiac function
D. results in activation of the baroreceptor reflex
E. causes bradycardia
Definition
Answer: A.

Sympathetic nerves innervating the heart increase heart rate.
Term
According to Poiseuille’s equation, blood flow in a vessel would be reduced by half when:
A. blood viscosity is halved.
B. vessel length is doubled.
C. vessel diameter is halved.
D. the pressure gradient along the length of vessel is doubled.
E. blood flow velocity is doubled.
Definition
Answer: B.
Term
Key mechanisms in combating orthostatic or postural hypotension include:
A. the baroreceptor reflex.
B. reduced distensibility of leg veins compared to thoracic veins.
C. muscle pumps.
D. all of the above.
E. none of the above.
Definition
Answer: D
Term
Which ONE of the following statements regarding blood vessels is INCORRECT?
A. Veins are sometimes called capacitance vessels.
B. Arterioles contain smooth muscle in their walls.
C. Arteries contain large amounts of elastic tissue in their walls.
D. Arterioles are sometimes called resistance vessels.
E. Capillaries contain smooth muscle in their walls.
Definition
Answer: E.

This is the incorrect statement. Capillary walls are made up of a single layer of endothelial cells and a basement membrane and do not contain muscle.
Term
Which ONE of the following is INCORRECT regarding the mechanism by which the substance moves across the wall of a capillary?
A. Net water transport depends upon net (hydraulic) filtration pressure.
B. Oxygen permeation is more than 1000 times faster than glucose permeation.
C. Urea diffuses across the wall down its concentration gradient.
D. Glucose is carried across the wall by plasma filtration.
E. Respiratory gases permeate rapidly, because they are lipid soluble.
Definition
Answer: D.

This is the incorrect statement. Transcapillary glucose transport is by diffusion down a concentration gradient.
Term
The function of the papillary muscles and chordae tendinae is to:
A. Keep the AV valves from bulging into the atria during ventricular contraction.
B. Increase backflow into the ventricles during diastole.
C. Hold open the semilunar valves during systole.
D. Hold the AV valves open during diastole.
E. Keep the AV valves from bulging into the aorta and pulmonary arteries during systole.
Definition
Answer: A.

The flaps of the AV valves are anchored to the papillary muscles of the ventricles by chordae tendinae. The papillary muscles pull the valves inwards towards the ventricles by exerting tension on the chordae tendinae and thus prevent or minimise the amount of bulging into the atria during systole.
Term
Which ONE of the following organs/tissues receives the greatest increase in systemic blood flow during exercise?
A. Brain.
B. Muscle.
C. Kidneys.
D. Skin.
E. Heart.
Definition
Answer: B.
Term
Which ONE of the following statements about an action potential generated from a sinus nodal fibre is INCORRECT?
A. The unstable baseline can be partly attributable to a progressive spontaneous reduction in membrane permeability to K+.
B. The unstable baseline can be partly attributable to a progressive decrease in Ca2+ permeability.
C. The resting membrane potential is about -60 mV.
D. Repolarisation is in part due to activation of K+ channels.
E. The sudden upstroke (depolarisation) is due to the opening of Ca2+ channels causing a rapid influx of Ca2+ into the cell.
Definition
Answer: B.

This is the incorrect statement. The unstable baseline can be partly attributable to a small progressive increase (not decrease) in Ca2+ permeability due to the opening of T (transient) channels.
Term
According to Poiseuille’s equation, reducing a blood vessel’s diameter by 20% would reduce blood flow in the vessel by (approximately):
A. 80%
B. 50%
C. 40%
D. 20%
E. 60%
Definition
Answer: E.

According to Poiseuille’s Law flow is proportional to the radius to the power of 4 (r4) of the conducting vessel. A 20% reduction in the diameter of a vessel would reduce flow by 0.84, which is 0.4096 - or a 60% reduction from the starting value.
Term
During which phase of the cardiac cycle are all four heart valves open?
A. isovolumetric ventricular contraction
B. all four heart valves are normally never open simultaneously
C. ventricular ejection
D. atrial systole
E. rapid and reduced filling
Definition
Answer: B.
Term
The volume reflex, in which heart rate and renal blood flow are increased following an increase in blood volume, is mediated primarily by:
A. a combination of atrial and vena cava baroreceptors, aortic baroreceptors and carotid sinus baroreceptors
B. carotid sinus baroreceptors
C. aortic baroreceptors
D. peripheral chemoreceptors
E. atrial and vena cava baroreceptors
Definition
Answer: E

Atrial and vena cava baroreceptors are sensitive to stretch of the wall of these vascular compartments, which is mainly caused by changes in blood volume, given the pressure in these compartments is usually very low (<3 mmHg).
Term
Blood flow velocity is slowest in ______ because this is where ______ is greatest.
A. capillaries, cross-sectional area
B. arterioles, resistance
C. veins, cross-sectional area
D. capillaries, resistance
E. aorta, cross-sectional area
Definition
Answer: A.

As the circulatory elements are arranged in parallel, the capillaries present the greatest total cross-sectional area within the entire circulatory system, therefore this is where blood flow velocity is the slowest.
Term
What is occurring during ventricular ejection?
A. The AV and semilunar valves are closed as ventricular pressure is increasing.
B. The AV valves are open and the semilunar valves are closed as ventricular pressure is increasing.
C. The AV valves are open and the semilunar valves are closed as blood is leaving the ventricles.
D. The AV valves are closed and the semilunar valves are open as blood is leaving the ventricles.
E. The AV and semilunar valves are open as blood is leaving the ventricles.
Definition
Answer: D
Term
Starling’s Law of the Heart means that when ventricular pre-load is increased, stroke volume will
A. decrease momentarily, then increase over time
B. stay the same
C. decrease
D. increase
E. increase momentarily, then decrease over time
Definition
Answer: D

Starling’s Law dictates that an increase in pre-load, will result in the stimulated ventricular muscle contracting with increased force. Thus more blood will be ejected during contraction, resulting in an increased stroke volume.
Term
The major mechanism controlling coronary artery diameter is:
A. venular constriction.
B. extracellular K+ concentration.
C. extracellular CO2 concentration.
D. sympathetic nerve activity.
E. accumulation of metabolic waste products.
Definition
Answer: E

The key mechanism increasing coronary blood flow is metabolic hyperemia, i.e. the dilation of coronary resistance arteries by accumulated metabolic waste products.
Term
Which ONE of the following is true of the ventricular filling phase of the cardiac cycle?
A. Ventricular pressure is increasing.
B. All valves in the heart are open.
C. Ventricular pressure is greater than atrial pressure.
D. Ventricular pressure is less than aortic pressure.
E. Ventricular filling occurs during systole.
Definition
Answer: D

Ventricular pressure is low and aortic pressure is much higher.
Term
During the rapid ejection phase of the cardiac cycle, which ONE of the following statements is INCORRECT?
A. The mitral valve is closed.
B. The ventricular volume is at its lowest.
C. The aortic pressure is rising.
D. The ventricular pressure approaches its maximum
E. The aortic valve is open.
Definition
Answer: B.

This is the incorrect statement. The ventricular volume does drop during this phase but actually reaches its lowest point during the reduced ejection phase.
Term
Stimulation of the heart by parasympathetic nerves
A. causes bradycardia
B. causes tachycardia
C. results in inhibition the baroreceptor reflex
D. results in activation of the baroreceptor reflex
E. has no effect on cardiac function
Definition
Answer: A.

Parasympathetic nerves represent the effector-arm of the baroreceptor reflex, and slow the heart rate (bradycardia).
Term
Myocardial contractility
A. cannot be altered by changes in heart rate
B. is increased by parasympathetic stimulation
C. cannot be altered under any circumstance
D. is increased by adrenaline
E. is decreased by sympathetic nerve stimulation
Definition
Answer: D.

Adrenaline increases the force of cardiac myocyte contraction by acting on beta-adrenergic receptors on the myocytes.
Term
A patient absorbs 300ml/min of oxygen.  The oxygen content of blood taken from the femoral artery = 18ml/100ml and blood taken from the pulmonary artery has an oxygen content of 13ml/100ml.  If the patient has a heart rate of 60 beats/min, the patient’s stroke volume is:
A. 80ml.
B. 10ml.
C. 12ml.
D. 100ml.
E. 120ml.
Definition
Answer: D.
Term
Which ONE of the following statements about the conduction system of the heart is INCORRECT?
A. The sinoatrial node is the normal pacemaker of the heart.
B. The Bundle of His receives impulses from the atrioventricular node.
C. Purkinje fibres have the fastest rate of conduction of all parts of the conducting system.
D. The atrioventricular node has a slower inherent rate of discharge than the sinoatrial node.
E. Electrical events can spread directly between atria and ventricles through gap junctions.
Definition
Answer: E.

This is the incorrect statement. Electrical impulses cannot spread directly between atria and ventricles. They must pass through the AV node. The atria are insulated from the ventricles by the atrioventricular groove.
Term
The repolarisation of pacemaker cells is due in part to:
A. an increase in the permeability of sodium.
B. a decrease in the permeability of sodium.
C. an increase in the permeability of calcium.
D. a decrease in the permeability of potassium.
E. an increase in the permeability of potassium.
Definition
Answer: E.

The repolarisation of pacemaker cells is due in part to an increase in the permeability of potassium and also in part due to a decrease in permeability of Ca2+.
Term
According to the Starling Equation, which ONE of the following would NOT be a factor in the net filtration pressure controlling the movement of water across the capillary wall?
A. The interstitial fluid pressure.
B. Hydrostatic (blood) pressure in the capillary.
C. The concentration of Na+ in the interstitial fluid.
D. The number and size of the pores in the capillary wall.
E. The plasma protein concentration.
Definition
Answer: D.

The number and size of the pores in the capillary wall would not be a factor in the net filtration pressure controlling the movement of water across the capillary wall. It may alter the volumes that move, but not the net pressure.
Term
The firing rate of aortic baroreceptors is increased by
A. activation of receptors in the right atrium.
B. decreased blood pressure.
C. increased blood pressure.
D. increased blood oxygen concentration.
E. decreased blood oxygen concentration.
Definition
Answer: C.
Term
An increase in myocardial contractility will result in:
A. decreased end-systolic volume and increased stroke volume.
B. increased end-systolic volume and increased stroke volume.
C. increased end-diastolic volume and increased stroke volume.
D. decreased end-diastolic volume and decreased stroke volume.
E. no change in end-systolic volume or stroke volume.
Definition
Answer: A

An increase in myocardial contractility will mean a greater proportion of the heart’s content of blood will be ejected during systole. So end-systolic volume will decrease and stroke volume will increase.
Term
Myogenic mechanisms involved in autoregulation of blood flow are activated by:
A. endothelium-derived vasoactive factors.
B. the [O2] in surrounding tissue.
C. the [K+] in surrounding tissue.
D. generation of local vasoactive substances.
E. altered intra-luminal blood pressure.
Definition
Answer: E.

Myogenic mechanisms result from the interaction between blood pressure and the resulting degree of stretch or tension in the vessel wall, and are independent of all other factors listed.
Term
Which ONE of the following statements is INCORRECT?  Increased sympathetic nervous system activity to the sinoatrial node:
Select one:
A. increases the frequency of action potentials generated.
B. causes an increase in heart rate.
C. allows threshold to be reached more quickly.
D. results in a less negative membrane potential at the end of repolarisation.
E. Decreases the slope of the spontaneous depolarization of these action potentials
Definition
Answer: E

This is the incorrect statement. Increased SNS activity would increase the slope of spontaneous depolarisation allowing threshold to be reached more quickly.
Term
The major mechanism(s) controlling the diameter of arteries in the skeletal muscle is
Select one:
A. myogenic  mechanisms
B. extracellular CO2 concentration
C. extracellular K+ concentration
D. accumulation of metabolic waste products
E. all of the above
Definition
Answer: E
Term
Blood that leaves the right ventricle and later enters the left ventricle must have passed through which of the following valves?
A. Aortic and Tricuspid valves.
B. Bicuspid/Mitral and aortic valve
C. Pulmonary valve only.
D. Bicuspid/mitral valve only.
E. Pulmonary and bicuspid/mitral valves
Definition
Answer: E.
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